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Articles from 2001 In October


Final Report on Foot and Mouth Disease

Filed Oct. 19, 2001

We have now had 16 days without a confirmed outbreak. Praise be – after eight terrible months, the outbreak could be over.

To recap, the appalling blunders made by our Government and the Ministry of Agriculture bureaucrats at the top (the people at the front-line of the outbreak however did sterling work) have lessons for everyone in the world.

  • The important report and recommendations published in 1969 after our last major outbreak were largely ignored or forgotten.
  • There was a fatal 5 day delay in freezing all animal movements, thus guaranteeing our local sheep market system spread the disease across the country like wildfire.
  • As a result the authorities, veterinarians, diagnostic laboratories, valuers and slaughter teams were totally overwhelmed, but the Ministry refused to admit for three weeks that the outbreak was out of control and rejected help.
  • Eventually the army was called in to help, but 3 weeks too late. (The 1969 report said call them in on Day 1.) They got control of the logistics, but it was still an uphill battle to contain it.
  • Slaughtered animals were left for days unattended and then the huge funeral pyres outraged the public. (The 1969 report said when possible bury on site, not burn, don’t move carcases around.)
  • Affected farm disinfection contracts were handed out with little control, resulting in abuse and profiteering. Once this was evident amazingly the Government refused to pay for any cleaning down at all for a whole week. The confusion jeopardised the control measures.
  • Even now the import of banned meat products is nowhere as strict in Britain as it is in Australia and N. America for example. Disgraceful!
  • Now, at the hopeful conclusion of the outbreak, the Government refuses to hold a public enquiry where those responsible are forced to give evidence on oath. Instead it is holding 3 of its own ‘investigations’ in camera! This has resulted in no fewer than 5 other regional enquiries to try to get at the truth and learn lessons. Already one has been held but the Ministry declined to send representatives to answer questions on their actions. The public is highly cynical of the whole investigative affair.

So what should the US do?

  1. Study our incompetent actions/lack of action and ensure your politicians and bureaucrats cannot go down the same paths.
  2. Redouble your efforts to keep FMD out.
  3. Have contingency plans in place at Federal and Local levels. This is absolutely essential.
  4. Ensure the State and private veterinary services have contingency plans and facilities in place.
  5. Ensure that your clever lawyers cannot obstruct these essential emergency measures which will seem draconian and appear to curtail civil liberties at the time. So get advance legislation in place beforehand of what must be done, or prohibited as the case may be.
  6. Study the whole question of ring-vaccination v. slaughter.
  7. Keep the animals’ welfare to the fore by making sensible humane decisions, not taking blanket pigeon-hole decisions willy-nilly as bureaucrats do. If not, your public may crucify livestock farming.
  8. In our case movement of people and vehicles kept the long tail alive.

BE PREPARED! YOU WILL GET FMD ONE DAY

Farewell from a bruised and battered farming Britain! The final cost? Looks like $325 for every man, woman and child. It could have been a tenth of the cost and agony, had the authorities been prepared, or had even taken notice of crucial recommendations which, with hindsight, now seemed to be dead correct!

Anthrax information available at special website

The American Society of Animal Sicence and the American Dairy Science Association have released a special issue of DASEE, (pronounced: Daisy) is an acronym for Dairy and Animal Science Electronic Executive Summaries, focused on anthrax information. With the recent outbreaks in Florida, New York and Washington, D.C., the information can help the animal industries protect the animals, food and public health against bioterrorism.

The site includes articles on research programs, public health and medical preparedness, anthrax in livestock and the use of anthrax as a biological weapon.

The site is located at http://www.fass.org/dasees

PRRS Virus Drags Down Performance

Porcine reproductive and respiratory syndrome (PRRS) continues to be an economically significant disease for the global swine industry. First identified in the late 1980s, it still frustrates pork producers and veterinarians around the world.

The PRRS virus can produce both a reproductive form of the disease in the breeding herd and a respiratory form in nursery and finishing pigs. Clinical signs of PRRS virus-induced reproductive disease include third trimester abortion, premature farrowing, higher levels of stillbirths, mummies and preweaning mortality.

Respiratory Form

The focus of this article, the respiratory form of PRRS, has been documented to induce annual losses of approximately $228/inventoried sow, secondary to poor growth rates, elevated mortality, reduced feed efficiency and increased postweaning treatment costs/pig.

The respiratory form of PRRS typically includes concurrent infection of PRRS virus and any number of opportunistic pathogens of a viral and/or bacterial nature. Common clinical signs include elevated levels of meningitis and septicemia in the nursery, due to PRRS virus co-infection with Streptococcus suis, Actinobacillus suis or Haemophilus parasuis.

In finishing, pneumonia may be due to infection with PRRS virus and swine influenza virus, Mycoplasmal pneumonia, Salmonella choleraesuis, or Actinobacillus pleuropneumonia.

The essential element in controlling the respiratory form of PRRS is the production of pigs that are free of the virus at weaning. In order to consistently achieve this high level of health, we must understand how PRRS is transmitted throughout the breeding herd and weaned pig populations, and how to accurately diagnose the point of infection in the pig's life.

PRRS Transmission

In most chronically infected farms, uncontrolled circulation of PRRS virus occurs in the breeding herd. These farms experience repeat outbreaks of PRRS-related reproductive disease that is often specific to gilt parities, along with the respiratory form of PRRS in weaned pigs.

PRRS infection of the nursery pig typically begins early in life, either by transplacental transmission (vertical spread) or from sow-to-pig (horizontal transmission) before weaning. Litters of infected pigs then provide a source of virus for older pigs in the nursery, leading to continuous cycling of virus throughout the population. Understanding these transmission factors is key to “stabilizing” the breeding herd.

Stability for PRRS is a frequently misunderstood concept and is often an improperly used term. In this article, a stable breeding herd is defined as a population of adult swine and their offspring, within which there is no detectable evidence of sow-to-sow or sow-to-pig transmission of the virus.

Following is a summary of current scientific work and review of “take home messages” from eight studies.

  1. PRRS virus persists in boars.

    PRRS virus produces persistent infections of the male reproductive tract and can be shed through semen. The increasing world dependence on the use of artificial insemination makes this a key point in PRRS control.

  2. PRRS virus subpopulations exist in chronically infected breeding herds.

    Within infected breeding herds, PRRS-positive and PRRS-naïve adult hogs can coexist. PRRS antibody testing of randomly selected sows has shown that while certain animals remain seronegative, others become seropositive. This suggests that while viral transmission occurs in the breeding herd, it is very sporadic and viral exposure is inconsistent. This is particularly evident in large, 1,000-plus-sow breeding herds.

  3. Improper replacement gilt management plays a major role in the maintenance of PRRS virus spread.

    Similar to porcine parvovirus, uncontrolled introduction of PRRS-naïve or acutely infected gilts perpetuates circulation of the virus within the breeding herd. The result is repeat cases of PRRS reproductive disease and the preservation of PRRS subpopulations — groups of uneven health status within the herd.

  4. Closing the breeding herd reduces PRRS virus circulation.

    Field data suggests an internal multiplication program or a four-month ban on replacement stock entries, together with segregation of gilt and sow herds, reduced PRRS spread and exposure in both groups. This improved level of stability in the breeding herd allowed for successful depopulation of the nursery and improvement of pig performance.

  5. Different PRRS strains can co-exist in a single infected farm.

    Molecular sequencing of PRRS virus isolates from chronically infected farms has indicated that three genetically diverse strains of PRRS could co-exist and circulate within a farm. Further evidence from the University of Minnesota Veterinary Diagnostic Laboratory suggests that up to five different strains have been detected in a single farm.

  6. The prevalence of PRRS-positive carrier sows in chronically infected breeding herds can be extremely low.

    Results from an infected breeding herd that had been closed to introductions of breeding stock for more than six months indicated that the level of chronically infected breeding animals was low (1.7%). The virus was isolated from lymph nodes of an infected sow. Experimental infection of naïve, 95-day pregnant sows using this isolate produced either clinically affected litters of fetuses, or entire litters of fetuses that appeared normal but were infected with PRRS virus.

  7. Persistently infected sows can shed PRRS virus to naïve sows.

    Long-term, persistent PRRS infection can occur in sows, and these sows serve as a source of PRRS for naïve sows. In experimental infection of 12 sows, viral shedding was detected from infected sows to naïve sows that were separated from each other by a fence, 49, 56, and 86 days later. Nine sows that didn't shed were sacrificed; persistent PRRS virus was detected in multiple tissues of all nine sows.

  8. PRRS spread occurs readily in weaned pigs.

    There are a number of ways PRRS virus can spread between nursery rooms, even with all-in, all-out (AIAO) pig flow. This is particularly true if facilities contain multiple rooms and different ages of pigs.

    A source of PRRS virus for recently weaned pigs is lateral transmission of PRRS from older, previously infected, 8- to 10-week-old pigs. Besides pigs, mechanical transmission of the virus can occur following exposure to contaminated coveralls, boots and needles.

    Although people do not appear to serve as carriers, PRRS has been recovered from hands following direct contact with experimentally infected pigs. Following hand washing with soap and warm water, the virus was eliminated.



PRRS Diagnostics

To control PRRS infections postweaning, it's crucial to use diagnostic testing to target when the pig is becoming infected. New tests such as polymerase chain reaction (PCR) and molecular sequencing have proven to be very helpful in understanding patterns of PRRS virus transmission within and between infected farms. The PCR test is much more sensitive than virus isolation, and results are available in a shorter period of time (24-48 hours). Molecular sequencing assists in identifying potential sources of new viral introduction to farms and differentiation of field isolates from vaccine virus.

Regarding the detection of PRRS antibodies, the IDEXX ELISA test is a serologic test used routinely in diagnostic laboratories worldwide. The ELISA (enzyme-linked immunosorbent assay) test detects the formation of PRRS virus antibodies 9-13 days after virus exposure. Results are reported in the form of a sample to positive (s/p) ratio; levels of 0.4 or higher are considered positive. Cross-sectional sampling by ELISA according to stage of production can be useful to determine the point of infection in the pig's life.

For a serological profile, collect 10 samples from the breeding herd, from recently weaned pigs, from 8- to 10-week-old nursery pigs and 5- to 6-month-old finishers. Larger breeding herds (>1,000 sows) may require larger sample sizes, such as 30 or 60. Sampling by parity may indicate whether a specific subpopulation within the herd, such as gilts, is susceptible to infection.

Your veterinarian can assist you in determining the proper number of samples to collect, according to herd size and your available budget.

Finally, realize that PRRS infection alone may have little impact on performance. Therefore, it is important to use clinical observations and production records, in conjunction with diagnostic data, to properly evaluate the impact of PRRS in your herd. Once the pattern of virus spread and the age in which the pigs are infected is determined, intervention strategies can be initiated.

Vaccine Control of PRRS

Due to the need for cell-mediated immunity to control PRRS, modified-live virus (MLV) vaccines are far superior to killed preparations.

While MLV products have the potential to shed in naïve populations following first herd vaccination, transmission of vaccine virus is not readily detected following revaccination with the same (homologous) vaccine strain.

Diagnostic profiling is especially critical when vaccinating to avoid immunizing pigs already infected, and to start vaccination at least four weeks before infection.

Proper handling of MLV vaccines is important to enhance viability and efficacy of the vaccination process.

As well, an adequate needle length is vital to insuring proper intramuscular administration. A 1½-in. needle is required for adult breeding animals; a 1-in. needle is required for finishers and a ½-in. needle for nursery pigs. The product must be rehydrated using the proper diluent, and administered within 24 hours following hydration. Using a designated syringe, rinsed with only with hot water (not disinfectant), is important to vaccine efficacy.

Nursery Depopulation

Besides the introduction of PRRS virus by infected pigs at weaning, PRRS can circulate in the nursery by the shedding of the virus from older, infected pigs to younger, susceptible pigs.

Nursery depopulation is a cost-effective way to stop lateral PRRS spread and control of the respiratory form of PRRS. Major advances in nursery pig daily gain, mortality, treatment cost and profitability have been published, following implementation of this strategy (Table 1).

The protocol of nursery depopulation consists of emptying all nursery rooms on a given day, washing and disinfecting each room and allowing the entire facility to remain empty for at least two days.

Due to the poor viability of PRRS virus outside the pig, extended periods of downtime can be avoided, enhancing facility utilization and still succeeding in virus elimination.

Disinfectants recommended include phenolic- or formaldehyde-based products, shown to reduce survivability of the virus in the environment. This strategy also works in PRRS-infected finishing groups.

The positive response to nursery depopulation has resulted in the practice of flowing eight-week batches of weaned pigs into facilities designed for AIAO, allowing for a regularly scheduled depopulation of the nursery every eight weeks.

Reducing Spread

Due to the potential of contaminated boots, coveralls, needles and hands to serve as mechanical vectors of PRRS, producers should frequently change needles, ideally between every sow, litter of nursing piglets and between pens of weaned pigs. This is especially critical in times of high susceptibility to PRRS infection, such as sows in the third trimester of gestation, or during periods of high virus load, when nursery pigs are 6-8 weeks old.

Furthermore, when producers are finished working with clinically affected pigs, they should change clothes, boots, and wash hands prior to contacting susceptible animals.

Producers should also avoid mixing poor-doing, older animals with younger stock, to reduce viral spread from room-to-room, and avoid disruption of AIAO pig flow.

Finally, ensure that nursery room ventilation systems are functioning properly for adequate air flow to pigs of all ages throughout the year.

PRRS Eradication

While nursery or finisher depopulation is very effective in eliminating postweaning PRRS infection, reinfection can occur following addition of infected weaners.

Therefore, elimination of persistently infected breeding animals, in conjunction with nursery and/or finisher depopulation can eliminate PRRS.

Test and removal was the first successful strategy for PRRS elimination. Test and removal consists of blood-testing the entire breeding herd in a single day, identifying PRRS-infected animals using both an antibody (ELISA) and a virus (PCR) test, and immediately removing positive animals from the farm. Limitations of this approach include a high degree of labor involved in a whole herd test, and diagnostic costs that approach $10/tested sow. Furthermore, a low seroprevalence (<10 %) of ELISA positive sows is required to reduce the impact of animal removal.

Conclusions

Postweaning PRRS infection still plays a major role in the porcine respiratory disease complex. Multiple tools for the diagnosis, control and eradication, along with new information on the epidemiology of the virus have enhanced the ability of producers and practitioners to reduce the economic impact of the disease.

Yet many questions still remain unanswered, and scientists throughout North America must work together to bring the knowledge to the industry as quickly as possible.

More information regarding the immunology and transmission of the virus, the availability of diagnostic tests to detect carriers and differentiate antibody responses produced from vaccine (vs.) infection are just a few critical, missing puzzle pieces.

Table 1. Mean Differences in Pig Performance from 34 Nurseries 12 Months Before and 12 Months After Nursery Depopulation.

Group #Farms ADG (lb.) Mortality Feed:Gain Treatment cost/pig**
Before After Before After Before After Before After
1 16 0.55 0.78* 9.7 2.3* 1.83 1.78 $1.75 $.96
2 7 0.55 0.78* 14.4 2.0* 2.00 1.85 $2.71 $1.33
3 5 0.64 0.82* 7.0 1.7* 2.06 1.85 $2.36 $1.57
4 6 0.57 0.90* 10.9 1.2* 1.95 1.70 $1.88 $1.06
Total 34 0.57 0.78* 10.2 1.9* 1.91 1.77 $1.88 $1.06
*= (p<0.0001)
**= Total cost of injectable and water soluble antibiotics and vaccines on a per pig basis.

New Center Targets Mycoplasma

There are a lot of benefits to disease eradication, says Carlos Pijoan, DVM, director of the University of Minnesota College of Agriculture's new Swine Disease Eradication Center. “Eradicating disease is probably the single biggest way we can have an impact on the cost of production, animal welfare and swine employee job satisfaction,” says Pijoan, professor of veterinary medicine. “Our mission is to develop and validate strategies and techniques that will help pork producers eliminate diseases.”

The center is based in St. Paul, MN. Six veterinary staff members are devoted exclusively to swine health issues, he says. Also, a commercial farm has been leased near Morris, MN, to conduct research to help with disease eradication protocols, he adds. More information on the center can be accessed at the college's Web site: www.cvm.umn.edu/sdec.

First Goal

The center's first goal is to look at eradication of Mycoplasmal pneumonia, says Pijoan, speaking at the first International Symposium on Swine Disease Eradication held during the Leman Swine Conference in Minneapolis.

Why Eradicate Mycoplasma?

Pijoan explains mycoplasma is one of the most insidious pathogens affecting the pig. It is found in the vast majority of hog farms worldwide, causing respiratory problems in growing pigs.

More recently, mycoplasma has been identified as playing a key secondary role in aggravating infections with porcine reproductive and respiratory syndrome (PRRS). It has been linked to a wide variety of other major disease problems including Actinobacillus pleuropneumonia (APP), pseudorabies and even Classical Swine Fever (hog cholera).

Although it has been difficult to document direct costs linked to mycoplasma, it's clear that farms that have managed to break free of the disease enjoy dramatic improvements in performance, especially with growth rates and feed efficiency, states Pijoan.

The Minnesota researcher is not the first to suggest eradication of mycoplasma. In fact, attempts for many years have provided mixed results.

One of the first attempts at eradication was by off-site rearing of litters from older parity sows. It was thought that older parity sows would clear infection so their litters would be free of the microorganism, recalls Pijoan. Many of these newly established herds seemed to be disease-free, but most ended up becoming reinfected.

“Recent work in our group using polymerase chain reaction (PCR) from nasal swabs has found a high prevalence of mycoplasma-positive females of older parities in conventional herds, which suggests that the original hypothesis that these herds were mycoplasma-free may have been flawed,” he says.

Current Efforts

Three techniques are being tried to eliminate mycoplasma:

  1. Hysterectomy and off-site rearing: This method used in the specific pathogen-free (SPF) herd programs works well. But it is an arduous task best left to preservation of genetic lines.

  2. Segregated early weaning (SEW): Research has shown that 5-day-old weaned pigs can be reared free of mycoplasma. This technique appears useful for the establishment of new herds, but is not practical for existing herds.

    Overall, SEW has proved successful where breeding stock companies have wanted to preserve bloodlines. But many other mycoplasma eradication efforts employing SEW have failed because producers cut corners or the technology simply didn't work.

    It is still uncertain if SEW really eliminates the mycoplasma organism, or the prevalence just drops below observable levels.

  3. Depopulation of younger animals: Recent European research has indicated it is possible to eliminate the mycoplasma organism by eliminating all pigs less than 10 months of age from the herd. Under this program, the next step is to stop farrowing and treatment of remaining sows with antibiotics for a two-week period. The plan has apparently worked in small herds.

    But Pijoan questions whether European herds have truly eliminated the organism — or if they are just blood test negative and are free of lesions at slaughter. He says recent research at Minnesota has shown animals can be infected by mycoplasma and not develop lesions or blood test positive.



Questions Abound

Many questions remain. Reinfections of apparently clean herds could mean that the organism is more efficient than most at area spread, or that it was in the herd all along and expressed itself when the pathogen population or stress reached a critical level.

Still, mycoplasma eradication is a worthy goal because of the bacteria's role as a central immunosuppressor. It produces a cascade of events, precipitates PRRS infection and facilitates pasteurella and APP infections. PRRS infections then lead to infections with Streptococcus suis and Haemophilus parasuis, he notes.

Elimination of mycoplasma would greatly reduce the use of subtherapeutic antibiotics (continuous, low level), cut costs and provide a much healthier hog at marketing, says Pijoan.

Viruses Alter Mycoplasma Pattern

The term enzootic pneumonia has commonly been used when referring to a syndrome observed in growing pigs that was characterized by cough, mild-to-moderate loss of appetite, uneven growth rates and a low number of pigs with active signs of pneumonia.

The primary cause of these conditions is Mycoplasmal pneumonia, with secondary bacteria including Pasteurella multocida playing a significant role. A large number of secondary bacteria have been associated with enzootic pneumonia.

Pneumonia Patterns Changed

In recent years, the pattern of respiratory disease in growing pigs has changed in many hog operations. This change coincides with the emergence of new viral diseases such as porcine reproductive and respiratory syndrome (PRRS) virus, porcine circovirus type 2 (PCV) and the new H3N2 strain of swine influenza virus (SIV). Well-known viral infections such as H1N1 SIV and pseudorabies (PRV) remain a problem, when present.

The emergence of viruses plays a role in changing the pattern of respiratory disease. Management practices also have had an impact. Those practices include increasing herd sizes, large numbers of pigs housed in the same air space and the resulting variation in immune status of the pigs.

With the involvement of viruses, the resulting respiratory syndrome is more severe than the disease induced by enzootic pneumonia and has been designated the porcine respiratory disease complex (PRDC).

PRDC, characterized by labored breathing, cough, fever, lethargy, depressed appetite and decreased rate of gain and feed efficiency, is a significant economic problem affecting pork production worldwide.

Many pathogens have been isolated from pigs with PRDC, including SIV, PRRS, PRV, Pasteurella multocida, Actinobacillus suis, Streptococcus suis, Actinobacillus pleuropneumonia, Haemophilus parasuis and mycoplasma. The most common PRDC pathogens isolated from pigs at the Iowa State Diagnostic Laboratory are mycoplasma, PRRS and SIV.

Mycoplasma/Pasteurella

Infection with only mycoplasma induces a mild chronic pneumonia consisting of well-defined, dark-red (acute) to tan-grey (chronic) areas of consolidation in certain regions of the lung. Live pigs infected with mycoplasma exhibit a sporadic cough with little effect on growth performance.

Pasteurella is generally considered an opportunistic bacterial pathogen. It rarely causes pneumonia by itself.

There are three serotypes of pasteurella that are important in pigs.

Dermonecrotic, toxin-producing strains are responsible for atrophic rhinitis, but less is known about strains involved with pneumonia.

Non-toxigenic strains of pasteurella are the most common secondary pathogen isolated from the respiratory tract of pigs with enzootic pneumonia. Pneumonia associated with pasteurellosis typically consists of red-grey cranioventral pneumonia with exudates (oozing materials) in the airways. Pleuritis is occasionally observed.

Growth of pasteurella in the respiratory tract may affect the cilia similar to the impact produced by mycoplasma. This further decreases the ability of the cells to clear bacteria and debris from the airways.

Studies have revealed a significant interaction between mycoplasma and pasteurella. One study determined that mycoplasma predisposed pigs to infection with pasteurella. Pigs infected with both organisms demonstrated increased severity of coughing and had difficulty breathing. No lesions were observed in the lungs of pigs infected with only pasteurella, in contrast to the severe pneumonia observed in pigs infected with both pathogens.

Likewise, the ability to isolate pasteurella changes when pigs are infected with mycoplasma. In one study, pasteurella was not isolated from experimentally infected pigs with the organism at two weeks following inoculation.

In contrast, pasteurella was isolated from three of four pigs infected with both pasteurella and mycoplasma. Similar findings were observed by Purdue University's Sandy Amass, DVM, et al., (1994), where pigs infected with both mycoplasma and pasteurella had significantly more pneumonia and respiratory disease problems than pigs experimentally inoculated with either pathogen alone.

Impact on Viral Disease

Mycoplasma's ability to increase the severity of respiratory disease is not limited to bacterial infections. In a study in our laboratory, mycoplasma increased the duration and severity of pneumonia induced by PRRS virus. Shibata, et al (1998) found that the presence of mycoplasma made pneumonia in pigs co-infected with PRV more severe.

The degree that mycoplasma influences the respiratory disease caused by other organisms varies. A study in our laboratory found that the pneumonia in pigs infected with mycoplasma and SIV was more additive in nature. While disease and pneumonia were more severe and lasted longer when the two were together, the pneumonia did not last as long as observed with joint PRRS and mycoplasma infections.

Mycoplasma Mechanisms

The mechanism, by which mycoplasma increases the severity of disease, in conjunction with other pathogens, currently is unknown. But, mycoplasma has been shown to have a negative effect on the immune system and causes chronic, long-term pneumonia.

Mycoplasma causes pneumonia by direct damage to the cells of the respiratory system. In addition, it appears to misdirect the responses of the host's immune system. Direct damage to the cells of the respiratory tract occurs when mycoplasma attaches to the cilia of the airway epithelial cells. This results in clumping and loss of cilia. The tiny, hair-like cilia in the respiratory tract work to clear organisms and debris from the lungs and airways. The loss of function of these cilia is thought to be a major contributor to the increased incidence of disease associated with secondary infections, especially pasteurella.

In addition, indirect changes to the immune system of the respiratory tract are a major part of mycoplasma infection. Mycoplasma diminishes the ability of the immune system of the respiratory tract to work efficiently and effectively. When mycoplasma causes chronic inflammation in the lungs, tissue damage occurs, which in turn increases the ability of opportunistic secondary bacteria such as pasteurella to develop and reproduce in the respiratory tract.

Mycoplasma also lessens the ability of white blood cells to clear debris and bacteria from the lungs, further increasing the damage caused by secondary bacterial infections.

While many questions remain about how mycoplasma causes pneumonia, even less is known about how the non-toxigenic strains of pasteurella induce disease.

An additional factor that may be involved in disease induced by pasteurella is lipopolysaccharide (LPS), an endotoxin, that is a component of the bacterial cell wall. LPS may also be an important factor in pasteurella's ability to induce damage by inflammation and disease in the lungs.

Diagnostic Challenge

Diagnosis of pneumonia caused by either pasteurella or mycoplasma remains challenging. The pneumonic lesions observed with either or both organisms can't be differentiated from most other bacterial pneumonias.

Diagnosis of pneumonia due to pasteurella infection is based on isolation of the organism from affected lung tissues or airways. Antibiotic sensitivity testing is recommended for selection of the appropriate treatment.

Diagnosis of mycoplasma is often based on observation of characteristic lesions and examination of lung tissue. A precise diagnosis with only observable or microscopic examination may be difficult as a number of other pathogens, including SIV, induce similar lesions.

Further testing is commonly undertaken to confirm mycoplasma infection. Culture and isolation of mycoplasma is difficult, labor intensive and takes weeks to complete.

Isolation of mycoplasma is also difficult as other, non-pathogenic mycoplasmas and bacteria commonly overgrow the cultures, further complicating the diagnosis. All of these problems make culture of mycoplasma impractical.

Polymerase chain reaction (PCR) assays are becoming increasingly popular for detection of mycoplasma and are frequently used to aid in strategically placing medication and vaccination programs. Serology is also widely used, although vaccination and the length of time (usually 3-6 weeks) for pigs to seroconvert to mycoplasma often makes it hard to determine the timing of infection.

Control Procedures

Control of the respiratory disease induced by mycoplasma and pasteurella is similar to that for all pathogens associated with PRDC. Proper management of production inputs, including environment, nutrition, biosecurity, weaning practices and all-in, all-out pig flow, have proven to be effective if protocols are followed diligently.

Antibiotic therapy also can be used for control of the pneumonia associated with pasteurella. A number of antibiotics are approved for use in the treatment of pasteurella, although antibiotic sensitivity testing is recommended to ensure that the appropriate therapy is used.

Various medication strategies are used to treat mycoplasma with varying degrees of success. There are few antibiotics that are effective against mycoplasma.

Vaccination

Vaccination is a common control method for mycoplasma. Amass, et al. (1994) demonstrated that mycoplasma vaccination decreased the severity of pneumonia in pigs infected with both mycoplasma and pasteurella. Mycoplasma vaccines have been shown to decrease the onset of PRRS-induced pneumonia caused by mycoplasma.

However, vaccination with a modified live virus PRRS vaccine and/or infection with PRRS during and after mycoplasma vaccination greatly reduced the efficacy of the mycoplasma vaccine with respect to mycoplasma-induced lesions. This suggests that vaccine effectiveness can be reduced by the presence of other diseases at the time of vaccination.

Vaccination for pneumonic pasteurellosis is not commonly practiced in the United States, although several products were commonly used from 15 to 25 years ago.

Mycoplasma and pasteurella are important pathogens associated with PRDC. While neither organism is very pathogenic alone, in combination, they increase the severity of pneumonia. Proper management and strategic timing of antibiotic therapy and vaccination are required to control the pneumonia these organisms induce, as well as the other pathogens associated with PRDC.

PRRS Virus Drags Down Performance

Porcine reproductive and respiratory syndrome (PRRS) continues to be an economically significant disease for the global swine industry. First identified in the late 1980s, it still frustrates pork producers and veterinarians around the world.

The PRRS virus can produce both a reproductive form of the disease in the breeding herd and a respiratory form in nursery and finishing pigs. Clinical signs of PRRS virus-induced reproductive disease include third trimester abortion, premature farrowing, higher levels of stillbirths, mummies and preweaning mortality.

Respiratory Form

The focus of this article, the respiratory form of PRRS, has been documented to induce annual losses of approximately $228/inventoried sow, secondary to poor growth rates, elevated mortality, reduced feed efficiency and increased postweaning treatment costs/pig.

The respiratory form of PRRS typically includes concurrent infection of PRRS virus and any number of opportunistic pathogens of a viral and/or bacterial nature. Common clinical signs include elevated levels of meningitis and septicemia in the nursery, due to PRRS virus co-infection with Streptococcus suis, Actinobacillus suis or Haemophilus parasuis.

In finishing, pneumonia may be due to infection with PRRS virus and swine influenza virus, Mycoplasmal pneumonia, Salmonella choleraesuis, or Actinobacillus pleuropneumonia.

The essential element in controlling the respiratory form of PRRS is the production of pigs that are free of the virus at weaning. In order to consistently achieve this high level of health, we must understand how PRRS is transmitted throughout the breeding herd and weaned pig populations, and how to accurately diagnose the point of infection in the pig's life.

PRRS Transmission

In most chronically infected farms, uncontrolled circulation of PRRS virus occurs in the breeding herd. These farms experience repeat outbreaks of PRRS-related reproductive disease that is often specific to gilt parities, along with the respiratory form of PRRS in weaned pigs.

PRRS infection of the nursery pig typically begins early in life, either by transplacental transmission (vertical spread) or from sow-to-pig (horizontal transmission) before weaning. Litters of infected pigs then provide a source of virus for older pigs in the nursery, leading to continuous cycling of virus throughout the population. Understanding these transmission factors is key to “stabilizing” the breeding herd.

Stability for PRRS is a frequently misunderstood concept and is often an improperly used term. In this article, a stable breeding herd is defined as a population of adult swine and their offspring, within which there is no detectable evidence of sow-to-sow or sow-to-pig transmission of the virus.

Following is a summary of current scientific work and review of “take home messages” from eight studies.

  1. PRRS virus persists in boars.

    PRRS virus produces persistent infections of the male reproductive tract and can be shed through semen. The increasing world dependence on the use of artificial insemination makes this a key point in PRRS control.

  2. PRRS virus subpopulations exist in chronically infected breeding herds.

    Within infected breeding herds, PRRS-positive and PRRS-naïve adult hogs can coexist. PRRS antibody testing of randomly selected sows has shown that while certain animals remain seronegative, others become seropositive. This suggests that while viral transmission occurs in the breeding herd, it is very sporadic and viral exposure is inconsistent. This is particularly evident in large, 1,000-plus-sow breeding herds.

  3. Improper replacement gilt management plays a major role in the maintenance of PRRS virus spread.

    Similar to porcine parvovirus, uncontrolled introduction of PRRS-naïve or acutely infected gilts perpetuates circulation of the virus within the breeding herd. The result is repeat cases of PRRS reproductive disease and the preservation of PRRS subpopulations — groups of uneven health status within the herd.

  4. Closing the breeding herd reduces PRRS virus circulation.

    Field data suggests an internal multiplication program or a four-month ban on replacement stock entries, together with segregation of gilt and sow herds, reduced PRRS spread and exposure in both groups. This improved level of stability in the breeding herd allowed for successful depopulation of the nursery and improvement of pig performance.

  5. Different PRRS strains can co-exist in a single infected farm.

    Molecular sequencing of PRRS virus isolates from chronically infected farms has indicated that three genetically diverse strains of PRRS could co-exist and circulate within a farm. Further evidence from the University of Minnesota Veterinary Diagnostic Laboratory suggests that up to five different strains have been detected in a single farm.

  6. The prevalence of PRRS-positive carrier sows in chronically infected breeding herds can be extremely low.

    Results from an infected breeding herd that had been closed to introductions of breeding stock for more than six months indicated that the level of chronically infected breeding animals was low (1.7%). The virus was isolated from lymph nodes of an infected sow. Experimental infection of naïve, 95-day pregnant sows using this isolate produced either clinically affected litters of fetuses, or entire litters of fetuses that appeared normal but were infected with PRRS virus.

  7. Persistently infected sows can shed PRRS virus to naïve sows.

    Long-term, persistent PRRS infection can occur in sows, and these sows serve as a source of PRRS for naïve sows. In experimental infection of 12 sows, viral shedding was detected from infected sows to naïve sows that were separated from each other by a fence, 49, 56, and 86 days later. Nine sows that didn't shed were sacrificed; persistent PRRS virus was detected in multiple tissues of all nine sows.

  8. PRRS spread occurs readily in weaned pigs.

    There are a number of ways PRRS virus can spread between nursery rooms, even with all-in, all-out (AIAO) pig flow. This is particularly true if facilities contain multiple rooms and different ages of pigs.

    A source of PRRS virus for recently weaned pigs is lateral transmission of PRRS from older, previously infected, 8- to 10-week-old pigs. Besides pigs, mechanical transmission of the virus can occur following exposure to contaminated coveralls, boots and needles.

    Although people do not appear to serve as carriers, PRRS has been recovered from hands following direct contact with experimentally infected pigs. Following hand washing with soap and warm water, the virus was eliminated.



PRRS Diagnostics

To control PRRS infections postweaning, it's crucial to use diagnostic testing to target when the pig is becoming infected. New tests such as polymerase chain reaction (PCR) and molecular sequencing have proven to be very helpful in understanding patterns of PRRS virus transmission within and between infected farms. The PCR test is much more sensitive than virus isolation, and results are available in a shorter period of time (24-48 hours). Molecular sequencing assists in identifying potential sources of new viral introduction to farms and differentiation of field isolates from vaccine virus.

Regarding the detection of PRRS antibodies, the IDEXX ELISA test is a serologic test used routinely in diagnostic laboratories worldwide. The ELISA (enzyme-linked immunosorbent assay) test detects the formation of PRRS virus antibodies 9-13 days after virus exposure. Results are reported in the form of a sample to positive (s/p) ratio; levels of 0.4 or higher are considered positive. Cross-sectional sampling by ELISA according to stage of production can be useful to determine the point of infection in the pig's life.

For a serological profile, collect 10 samples from the breeding herd, from recently weaned pigs, from 8- to 10-week-old nursery pigs and 5- to 6-month-old finishers. Larger breeding herds (>1,000 sows) may require larger sample sizes, such as 30 or 60. Sampling by parity may indicate whether a specific subpopulation within the herd, such as gilts, is susceptible to infection.

Your veterinarian can assist you in determining the proper number of samples to collect, according to herd size and your available budget.

Finally, realize that PRRS infection alone may have little impact on performance. Therefore, it is important to use clinical observations and production records, in conjunction with diagnostic data, to properly evaluate the impact of PRRS in your herd. Once the pattern of virus spread and the age in which the pigs are infected is determined, intervention strategies can be initiated.

Vaccine Control of PRRS

Due to the need for cell-mediated immunity to control PRRS, modified-live virus (MLV) vaccines are far superior to killed preparations.

While MLV products have the potential to shed in naïve populations following first herd vaccination, transmission of vaccine virus is not readily detected following revaccination with the same (homologous) vaccine strain.

Diagnostic profiling is especially critical when vaccinating to avoid immunizing pigs already infected, and to start vaccination at least four weeks before infection.

Proper handling of MLV vaccines is important to enhance viability and efficacy of the vaccination process.

As well, an adequate needle length is vital to insuring proper intramuscular administration. A 1½-in. needle is required for adult breeding animals; a 1-in. needle is required for finishers and a ½-in. needle for nursery pigs. The product must be rehydrated using the proper diluent, and administered within 24 hours following hydration. Using a designated syringe, rinsed with only with hot water (not disinfectant), is important to vaccine efficacy.

Nursery Depopulation

Besides the introduction of PRRS virus by infected pigs at weaning, PRRS can circulate in the nursery by the shedding of the virus from older, infected pigs to younger, susceptible pigs.

Nursery depopulation is a cost-effective way to stop lateral PRRS spread and control of the respiratory form of PRRS. Major advances in nursery pig daily gain, mortality, treatment cost and profitability have been published, following implementation of this strategy (Table 1).

The protocol of nursery depopulation consists of emptying all nursery rooms on a given day, washing and disinfecting each room and allowing the entire facility to remain empty for at least two days.

Due to the poor viability of PRRS virus outside the pig, extended periods of downtime can be avoided, enhancing facility utilization and still succeeding in virus elimination.

Disinfectants recommended include phenolic- or formaldehyde-based products, shown to reduce survivability of the virus in the environment. This strategy also works in PRRS-infected finishing groups.

The positive response to nursery depopulation has resulted in the practice of flowing eight-week batches of weaned pigs into facilities designed for AIAO, allowing for a regularly scheduled depopulation of the nursery every eight weeks.

Reducing Spread

Due to the potential of contaminated boots, coveralls, needles and hands to serve as mechanical vectors of PRRS, producers should frequently change needles, ideally between every sow, litter of nursing piglets and between pens of weaned pigs. This is especially critical in times of high susceptibility to PRRS infection, such as sows in the third trimester of gestation, or during periods of high virus load, when nursery pigs are 6-8 weeks old.

Furthermore, when producers are finished working with clinically affected pigs, they should change clothes, boots, and wash hands prior to contacting susceptible animals.

Producers should also avoid mixing poor-doing, older animals with younger stock, to reduce viral spread from room-to-room, and avoid disruption of AIAO pig flow.

Finally, ensure that nursery room ventilation systems are functioning properly for adequate air flow to pigs of all ages throughout the year.

PRRS Eradication

While nursery or finisher depopulation is very effective in eliminating postweaning PRRS infection, reinfection can occur following addition of infected weaners.

Therefore, elimination of persistently infected breeding animals, in conjunction with nursery and/or finisher depopulation can eliminate PRRS.

Test and removal was the first successful strategy for PRRS elimination. Test and removal consists of blood-testing the entire breeding herd in a single day, identifying PRRS-infected animals using both an antibody (ELISA) and a virus (PCR) test, and immediately removing positive animals from the farm. Limitations of this approach include a high degree of labor involved in a whole herd test, and diagnostic costs that approach $10/tested sow. Furthermore, a low seroprevalence (<10 %) of ELISA positive sows is required to reduce the impact of animal removal.

Conclusions

Postweaning PRRS infection still plays a major role in the porcine respiratory disease complex. Multiple tools for the diagnosis, control and eradication, along with new information on the epidemiology of the virus have enhanced the ability of producers and practitioners to reduce the economic impact of the disease.

Yet many questions still remain unanswered, and scientists throughout North America must work together to bring the knowledge to the industry as quickly as possible.

More information regarding the immunology and transmission of the virus, the availability of diagnostic tests to detect carriers and differentiate antibody responses produced from vaccine (vs.) infection are just a few critical, missing puzzle pieces.

Table 1. Mean Differences in Pig Performance from 34 Nurseries 12 Months Before and 12 Months After Nursery Depopulation.

Group #Farms ADG (lb.) Mortality Feed:Gain Treatment cost/pig**
Before After Before After Before After Before After
1 16 0.55 0.78* 9.7 2.3* 1.83 1.78 $1.75 $.96
2 7 0.55 0.78* 14.4 2.0* 2.00 1.85 $2.71 $1.33
3 5 0.64 0.82* 7.0 1.7* 2.06 1.85 $2.36 $1.57
4 6 0.57 0.90* 10.9 1.2* 1.95 1.70 $1.88 $1.06
Total 34 0.57 0.78* 10.2 1.9* 1.91 1.77 $1.88 $1.06
*= (p<0.0001)
**= Total cost of injectable and water soluble antibiotics and vaccines on a per pig basis.

News Updates

Missouri Pricing Law Changed

Missouri Gov. Bob Holden has signed a law to revise the state's controversial livestock marketing law.

Holden's signature reverses the law that went into effect May 29, which said packers could not discriminate in the prices they offered producers for livestock of similar quality.

The old law had a chilling effect on hog and beef purchases in the state, as packers avoided the risk of price discrimination lawsuits and markets for livestock were reduced.

University of Missouri agricultural economist Ron Plain estimates the state's pork producers lost $1.4 million under the old law.

The new law mirrors provisions in the federal Packers and Stockyards Act. The state department of agriculture is allowed to refer violations of the law to the attorney general, who has the authority to file lawsuits against price discrimination.

BSE Impact on Pork

Bovine Spongiform Encephalopathy (BSE) will affect the pork industry, even though the disease has not yet been detected in pigs, says Will Hueston, DVM.

“Absence of evidence is not evidence of absence. It is difficult to prove that a species is not susceptible and the remaining uncertainty, international trade restrictions on meat products, and consumers' food safety concerns will have an impact on swine producers,” says Hueston. He is director of the Center for Animal Health and Food Safety at the University of Minnesota.

Even without evidence of BSE in live pigs, some scientists are concerned that the BSE agent could be sequestered in pig tissue and pigs could be silent carriers of the disease, he pointed out in an address at the Leman Swine Conference in Minneapolis. Hogs fed BSE-contaminated feedstuffs could also expose other species by shedding the agent into the environment, says Hueston, who served six years on the United Kingdom BSE Advisory Committee.

He expects consumer concerns will rise as BSE is identified in other countries and more cases of variant Creutzfeldt-Jakob disease are diagnosed. The pork industry must be ready for the communications challenge that comes with the uncertainty about the disease and the continued media attention, he stresses.

Disease Conference

The Ninth Annual Swine Disease Conference for Swine Practitioners hosted by Iowa State University is slated for Nov. 8-9 in Ames, IA.

The first day's program focuses on farrowing health concerns, biosecurity, artificial insemination, audit systems and a health update.

The second day covers porcine reproductive and respiratory syndrome (PRRS), food safety and public health concerns, health and welfare issues and postweaning multisystemic wasting syndrome.

Register by mail: Continuing Education and Communication Services, c/o Janet Gardner, 102 Scheman Building, Iowa State University, Ames, IA 50011-1112; by fax: (515) 294-6223; or online: www.lifelearner.iastate.edu/conference/online.htm. For details, call: (800) 262-0015 or e-mail: jrgard@iastate.edu.

Federal Bribery Charges Filed

The U.S. District Court in Minneapolis has filed federal bribery charges against the Rock County, MN, director of land management and soil and water conservation, and Global Ventures, Inc., a Pipestone, MN, pork production company.

According to the indictment, John Burgers failed to report to the state pollution control agency a March 1996 spill of potentially hazardous waste at a Global Ventures production site. Later that same year, Global Ventures officials allegedly assisted Burgers in arranging $100,000 in loan consolidations through a local bank and provided him with $6,000 cash to pay down the loan.

Global Ventures released this statement: “Global Ventures vehemently denies these unfounded accusations that it engaged in any illegal activities with Mr. Burgers. Global Ventures is confident that it will be totally vindicated of any charges.”

The Minnesota Pollution Control Agency is investigating feedlot practices in the county, while county officials are conducting their own investigation. Burgers has been placed on administrative leave.

Manure Storage Book

A new, 120-page book on building manure storage structures can be ordered through the University of Minnesota.

“Manure Storages,” MWPS-18, Section 2 was developed by Midwest Plan Service (MPWS). It covers selecting and sizing a storage facility, choosing and preparing a site, constructing earthen impoundments, monitoring and managing a facility and proper plans for closing an earthen storage facility.

Cost is $15 plus sales tax per copy. To order, contact MWPS Orders, 219 Biosystems and Agricultural Engineering, University of Minnesota, 1390 Eckles Ave., St. Paul, MN 55108; phone: (612) 625-9733; e-mail: mwps@gaia.bae.umn.edu, or go to the Web site: www.bae.umn.edu.

Pork Ahead of Curve

Two pork items are part of the dozen foods that show the greatest increases in sales in the 2001 Restaurants and Institutions Menu Census.

The barbecued pork sandwich ranked fifth and pulled pork sandwich ranked twelfth. The pulled pork sandwich jumped 59% in popularity from the survey two years ago.

“The increase in the pork that comes from shoulder cuts is important because that's a part that's typically underutilized,” says Steve Schmeichel, Hurley, SD, pork producer and chairman of the National Pork Board's Demand Enhancement Committee. “This leading foodservice magazine survey echoes what checkoff-funded research has shown,” he says. “It also shows that we're ahead of the curve on the ethnic cuisine currently being served and likely to be added to the menus.”

Oklahoma Odor Rule

The Oklahoma Board of Agriculture has passed new, stiffer emergency rules for hog odors. The rules, expected to be signed by Gov. Frank Keating, force producers to act if neighbors file complaints.

Under the rule, neighbors who live within two miles of an operation of more than 2,500 pigs must file three valid odor complaints.

Once that happens, the producer must work with the state agriculture department to design an abatement plan. The producer must also agree to not spread manure onto land on weekends, state holidays or if wind speed exceeds 20 mph.

Swine Reproduction Seminar

A seminar on swine reproduction is scheduled for Dec. 12 at the University of Illinois Extension Building at the state fairgrounds in Springfield.

The program focuses on increasing swine breeding herd efficiency and the latest tips on reproductive management.

For a copy of the program or more information, contact Rob Knox at (217) 244-5177 or by e-mail at rknox@uiuc.edu. Register by calling (217) 782-4617.

Trade Promotion Authority

National Pork Producers Council (NPPC) President Barb Determan is urging Congress to schedule a vote on granting Trade Promotion Authority (TPA) to President George Bush.

“Congress is united like never before,” says the Early, IA, pork producer leader. “The United States is showing the world how to work together to achieve a common goal. Surely, in this spirit of achievement and inclusion, Congress can break the impasse over trade that is smothering the economic progress of American farmers and ranchers.”

TPA has not been renewed since 1994. It gives the president the authority to negotiate trade agreements that Congress can either approve or reject, but not amend.

“The only way our farmers and ranchers will succeed is through free trade and that can't happen in a meaningful way without TPA,” says Determan. U.S. agricultural tariffs average 12%, while global tariffs on agricultural imports average 62%. “We need TPA now so we can level the playing field and create new opportunities for our producers,” she says.

Veterinarian's Annual Meeting

The American Association of Swine Veterinarians (AASV) 33rd annual meeting will be March 2-5, 2002 at the Westin Crown Center in Kansas City, MO. Conference focus is “Exceeding Expectations.”

Pre-conference workshops, March 2 and 3, will provide in-depth information on data management tools, swine reproduction, making predictions and projections, ventilation, diagnostic skills for the practitioner, nutrition, communication, financial planning, foreign animal disease, pharmaceutical issues and advances in circovirus and porcine reproductive and respiratory syndrome (PRRS) research.

The March 4 general session will be highlighted by the Howard Dunne Memorial Lecture presented by Tim Blackwell, DVM, Ontario, Canada.

Concurrent sessions March 4-5 highlight reemerging diseases, research, audits, human resources, production and finishing management and PRRS.

For more information, contact the AASV, 902 1st Ave., Perry, IA, 50220; phone: (515) 465-5255; fax: (515) 465-3832; e-mail: aasv@netins.net; Web site: www.aasv.org.

Cash Market Stabilizes

A review of information from the USDA mandatory price reporting system shows the percentage of hogs sold on the cash market has stabilized.

"We believe this may signal a leveling of the decline that we have seen during the past few years," says Glenn Grimes, University of Missouri agricultural economist.

Data shows 17.3% of hogs marketed between Aug. 6 and Sept. 15 were in negotiated sales. That matches negotiated sales figures from January of this year.

"We have speculated for several years that the proportion of hogs sold through negotiated sales would reach some plateau or equilibrium," says Steve Meyer, director of economics for the National Pork Board. "Maybe we have found that level where both producers' and packers' confidence in the spot market wanes, thus, leading them to not put more hogs under contract. Only time will tell if this is true."

Animal Rights Moderation

Leaders of animal rights organizations are preaching moderation. They are asking followers to tone down the negative rhetoric of the Bush Administration, reports the National Pork Producers Council.

A memo sent recently directing the Sierra Club staff to "cease bashing President Bush" in light of the terrorist attaches. The Sierra Club said it had taken all its ads off the air, halted phone banks and removed any anti-Bush materials from its Web site.

Other groups, including PETA (People for the Ethical Treatment of Animals), are following suit. "We will continue to fight animal abuse wherever we see it, but at least for the immediate time period, we'll focus on ways that do not involve public protest," says vegan campaign spokesman Bruce Friedrich, explaining the group's cancellation of protests at the World Dairy Expo held in early October in Madison, WI.

Ten Practices To Promote Herd Health

Most producers agree that the best way to deal with respiratory disease is prevention. But prevention often means vaccination or medication with little regard to the production practices that promote health.

Promoting health is a 24-hours-a-day, seven-days-per-week job, whereas disease prevention strategies are viewed as short-term activities, that are expected to yield outstanding results.

Unfortunately, the underlying biology of the pigs, the bugs and their association are not very forgiving. A short-term lapse in promoting health can have long-term consequences in the pig. Disease can occur within hours, days or weeks after the lapse.

Problems in the finisher actually start in the nursery or farrowing room. Our ability to understand when these lapses occur is hampered by how well we observe the pigs and their environment.

Numerous studies prove the impact of environment on respiratory disease. Yet objective evaluations of the environment are rarely part of a problem-solving strategy for respiratory disease.

Also, observations occur during the day, and we have no idea what happens at night.

Finally, the health of all pigs in the population needs to be promoted. For example, it is rare to find a nursery “comfort board” that is large enough to handle all the pigs in the pen.

Tips for Healthier Hogs

The following production practices apply to pigs of all ages.

  1. Provide effective environmental temperature (EET). This is influenced by air temperature, air velocity across the pig, floor (contact) temperatures, wall/ceiling (radiant) temperatures, moisture/humidity, zone heating and bedding. Accurate measurement of the individual parts holds the key to providing the proper EET.

    Air temperature is easily measured by a standard thermometer, but temperature changes over time are often more important. High-low thermometers serve as useful monitoring tools. In barns with reoccurring problems, continuous-recording thermometers often reveal sudden temperature fluctuations that substantially contribute to the problem. Surface temperatures are best measured using an infrared thermometer.

    Air velocity can be estimated by observing smoke movement patterns, but objective measurement of air speed requires an air flow meter.

    Assessing EET is critical for diagnosing problems in suckling and nursery pigs that are prone to chilling because of their small body size. Pig behavior such as sleeping and dunging patterns will tell you if the EET is improper. But evaluate the components of EET in order to make the necessary adjustments.

  2. Control gas levels. Gases of concern include water (humidity), oxygen, ammonia, carbon dioxide, carbon monoxide and, of course, hydrogen sulfide.

    The ventilation system should be viewed as an extension of the pig's respiratory tract. The pig breathes in oxygenated air and exhales carbon dioxide-containing air.

    Heaters use oxygen to burn fuel, producing carbon dioxide (clean burning) or carbon monoxide (incomplete combustion).

    Ammonia is often used to evaluate gas levels because we can smell it. In my experience, ammonia is not a good indicator of ventilation quality because the levels can be greatly influenced by the waste handling system.

    Measuring carbon dioxide levels provides a better indication of ventilation rates but requires specialized measuring devices. In the past two years, I've investigated several cases of poor nursery performance that were directly attributed to high carbon dioxide levels, even though ammonia and humidity levels were acceptable.

    Gas levels are dependent on the ventilation rate and correct mixing of fresh air with stale air. With mechanical, negative pressure systems, I have yet to see a situation where the “20-foot rule” does not apply. The 20-foot rule states that wherever you are standing in a room, you should be no more than 20 feet from an inlet. Designs that fail to follow this rule either have dead spots or turbulence in the microenvironments where pigs live.

  3. Proper stocking density is a controversial subject. Requirements for top production in one phase may be different than those for the next phase.

    For example, inadequate space in the late nursery phase, which is commonly observed, can promote disease in the finisher. Stocking density also impacts feeder space and drinker availability. Stocking rates should be based on the space requirements of the pigs as they exit the production phase.

  4. Ensure food and water availability. Food access is mostly a problem in the early nursery phase; the presentation of the diet can dramatically impact feed intake.

    Failure to promote feed intake in small pigs by gruel feeding or using special diets creates a subpopulation of animals more susceptible to disease.

    Water availability issues are mainly a challenge for the weaned pig. Regardless of age, pigs can suffer from an inadequate water supply. An important defense mechanism in the respiratory tract is the removal of debris and pathogens by the mucociliary escalator apparatus. Proper hydration of the animals is important for maintaining this apparatus.

  5. Segregate pig flow (all-in, all-out production) by room, building or site depending on disease concerns. For viral diseases, site separation is often required, although some diseases can travel between sites. Building and room layout within continuous flow sites will also influence health status. Segregated production also implies that all aspects of the facilities are thoroughly cleaned and disinfected between batches of pigs.

  6. Realize that operation (population) size influences the pattern of disease spread within a herd. Larger herds typically take longer to develop whole herd immunity and the dose of organisms can progressively increase as the disease spreads through the herd. Pig density also influences the effectiveness of the ventilation system. The bottom line is that large herds must make fewer mistakes.

  7. Reduce vertical transmission from sows to pigs. This can be accomplished by reducing weaning ages, stabilizing the immune status of the breeding herd or by eliminating disease.

  8. Store vaccines and medications for product effectiveness. Refrigerators should be monitored daily for temperature. High temperatures or freezing will ruin many products. Overstocking can result in poor air circulation and uneven temperatures within the refrigerator.

    All vaccines and medications should be stored in a clean and dry environment. Attention should be paid to proper injection techniques, dosages and withdrawal times. Expired products should be discarded or returned to the supplier.

  9. Address biosecurity needs externally and internally. Internally, design procedures for moving people, animals and equipment that reduce disease transmission within the herd.

    External biosecurity is dependent on a number of issues, including purchased animals, animal transport vehicles and truck drivers, wild animals, proximity to other farms, repair personnel and their equipment and visitors.

  10. Provide accurate and timely diagnostic testing to determine which disease is causing the problem. Diagnosis of a specific respiratory disease-causing agent is nearly impossible by simply observing the lung tissue during a postmortem examination. Follow-up laboratory testing is the only way to make this determination.

    Promoting health through proper production practices holds the key to controlling respiratory disease.


Host of Diseases Fuel Respiratory Ailments

There are several pathogens that can cause swine respiratory disease problems. There are also secondary disease problems that are less frequent or severe, meaning diagnosis and, sometimes, control are more difficult.

Pleuropneumonia

This term refers to diseases in which the lung and the pleura (lung membrane) are involved, in contrast to diseases such as Mycoplasmal pneumonia, where only the lung is affected. Pleuropneumonia is usually more devastating than pneumonia, often associated with acute death loss. It also tends to affect older pigs, usually at finishing.

Pleuropneumonia is present in many U.S. hog operations, although it is definitely less prevalent than it was 10 years ago when the disease was the main cause of mortalities. The sharp decline in prevalence is mostly related to changes in production systems.

Originally, pleuropneumonia was effectively reduced by widespread use of depopulation/repopulation strategies that were used in the late '80s. Later, the widespread adoption of segregated early weaning (SEW) had a very positive impact on this disease.

However, outbreaks of pleuropneumonia are still relatively common, which makes understanding this disease all the more relevant.

Types of Pleuropneumonia

There are two main, similar bacterial pathogens involved in pleuropneumonia — Actinobacillus pleuropneumonia (A. pleuropneumonia) and Actinobacillus suis (A. suis).

A. pleuropneumonia can be isolated from a large percentage of healthy hogs at slaughter, which suggests the presence of the organism is too low to trigger disease.

Both Actinobacilli are very prevalent in swine herds and both cause extensive pulmonary damage, characterized by areas of necrosis (tissue death), hemorrhage and edema (fluid-filled tissues).

And, both pathogens cause disease through the secretion of a special group of toxins that target the macrophage (pathogen-eating cells). Since this cell is a primary lung defense mechanism, its' inactivation by the toxins renders the host very susceptible to rapid spread of the toxins.

Macroscopic (visible to the naked eye) lesions are very typical, usually affecting large portions of the lung and characterized by black-red discoloration and pleural adhesions. Surviving pigs, however, quickly recover and may reach slaughter with few or no lesions indicative of the disease. The best indicator at slaughter of a problem is the presence of pleuritis.

Although the Actinobacilli are not the only agents that cause pleuritis in the pig, they are the most common, so that the presence of pleuritis at slaughter needs to be investigated further.

Surprisingly, Actinobacillus is restricted to the thoracic cavity. Although it can be occasionally isolated from other organs, lesions are pretty much restricted to the lung and pleura, as well as adjacent membranes.

A. suis has been connected with a variety of lesions other than pleuropneumonia, including skin lesions reminiscent of erysipelas. But most isolations identified in diagnostic laboratories are from animals showing signs and lesions of pleuropneumonia, indistinguishable from those caused by A. pleuropneumonia.

Pleuropneumonia Treatment

Both Actinobacilli are susceptible to a variety of antibiotics, including penicillin and cephalosporins. But effective treatment can only be achieved through injectable medication, since the extensive necrosis and vasculitis (inflammation of a blood or lymph vessel) prevents oral medication from reaching the affected sites. This makes treatment expensive and difficult.

Vaccination against A. pleuropneumonia is partially effective with traditional killed bacterins, giving some protection against death loss but not against infection or growth retardation. More effective vaccines, using inactivated toxins, are available in other countries, but are not presently licensed in the U.S. There are no licensed vaccines available against A. suis.

Autogenous vaccines for A. suis have a reputation of effectiveness. But they should only be used after a careful diagnostic workup has been done, together with a realistic financial evaluation of the expected benefits.

Streptococcus suis, Haemophilus parasuis

Streptococcus suis (S. suis) and Haemophilus parasuis (H. parasuis) have become very common pathogens of modern, high-health farms and represent a major source of loss to the industry. Both organisms show many similarities, yet differ in many respects. For example:

  • Both pathogens are members of the pig's normal flora, being present in practically all swine populations.

  • Both pathogens have a large variety of serotypes (35 for S. suis; over 15 for H. parasuis). There appears to be limited cross-protection between serotypes, which hinders effective vaccination with killed bacterins.

  • Although pig groups are infected by many different strains, only a few (usually one) strains actually cause disease in a given population. This suggests that there are virulent strains, although their difference with respiratory, non-virulent strains is not well understood.

  • They can both be commonly recovered from pulmonary tissues from both affected and non-affected animals.

  • Both cause systemic disease, characterized by neurological signs, lameness and breathing difficulty.

  • Disease is commonly seen 4-5 weeks after weaning, suggesting that it is related to a drop in maternal antibody protection. It may also be related to Porcine Reproductive and Respiratory Syndrome (PRRS) virus, since this virus circulates in the nursery at approximately the same time.

  • S. suis causes few, if any, visible lesions and is rarely linked to pneumonia or pleuritis. The most obvious lesion is vegetative endocarditis (inflammation of the heart lining).

  • In contrast, H. parasuis causes extensive necropsy lesions, fluid-filled cavities and lameness. In susceptible animals, H. parasuis can also produce a pneumonia, which is visibly unidentifiable from that produced by mycoplasma.



Disease caused by these two similar pathogens is more prevalent in SEW farms than in conventional, one-site facilities. This suggests that off-site weaning is somehow related to an increased problem.

In our view at the University of Minnesota Swine Center group, this may be caused by the slower spread of organisms in off-site nurseries, since the only infection source is piglets that became infected before weaning. This delayed infection produces clinical disease when piglets that have lost their maternal immunity become infected.

In contrast, nurseries in one-site farms get infected rapidly from disease spread through adjacent grow-finish units.

Our swine group has shown that by increasing the infection rate of lactating piglets (by experimentally infecting them), disease and treatment rates are effectively lowered. This proves our working hypothesis is probably correct. This experimental method for protection shows some promise, although many of the safety issues involved have to be addressed before it can be used commercially.

As noted, the presence of PRRS virus in the group may be another contributing factor. Disease caused by S. suis is more severe following PRRS infection. However, this has not been demonstrated for H. parasuis, although clinically the two diseases are often seen together. At this point, the role of PRRS in these secondary disease problems is debatable.

‘Suis’ Disease Treatment, Vaccination

Treatment with penicillin or cephalosporins is usually effective in very early infections, but only about 50% of animals showing clinical signs are saved. Surviving animals may have considerable growth retardation, making treatment not very cost-effective.

Vaccination against S. suis hasn't been very successful. Veterinarians report better success with sow vaccination but results haven't been well documented.

In contrast, H. parasuis responds well to vaccination with vaccines prepared with homologous or like serotypes. Unfortunately, there are at least 15 serotypes of this organism, making protection with commercial, licensed products variable.

Another option with H. parasuis is to use autogenous vaccines, which can work well if properly prepared. It is very important that the right strains be selected for these vaccines. This requires submitting several isolates from non-respiratory sites for genetic typing, to allow selection of the prevalent virulent strain on the farm to be used in the vaccine.

Postweaning Wasting Syndrome

There are many reports of the appearance of Postweaning Multi-systemic Wasting Syndrome (PMWS) in Canada and Europe (See “Disease Cases Climb; Cause Remains Elusive,” Feb. 15, 2001 National Hog Farmer, pages 28-29).

This is an ill-defined condition characterized by debilitated weaned pigs that frequently show respiratory distress together with other, more generalized signs of disease. Circovirus type 2 can frequently be demonstrated by lesions, both in lungs (that have interstitial pneumonia) and especially in lymph nodes.

These signs and some of the lesions are also found in animals affected by PRRS. In fact, PRRS virus can be demonstrated in most PMWS cases. This has made it difficult to interpret the role that circovirus plays in this problem, and how much PMWS is actually different from PRRS. There are probably also some differences between countries, presumably related to the relative virulence of PRRS.

In Europe, where PRRS is a milder disease, PMWS appears to be an important and common problem. The situation is more debatable in countries that have the severe American strains of PRRS, making it much more difficult to differentiate the two diseases.

In both PMWS and circovirus, weaned pigs, usually at 4-6 weeks after entry into the nursery, present a systemic syndrome characterized by extreme weakness, enlarged lymph nodes and difficult breathing. Visible lung lesions are unremarkable; the lungs usually don't collapse and frequently have a tan coloration. Histological (tissue) observation reveals massive interstitial pneumonia, the hallmark of these viral infections.

There are no specific treatments or vaccines available for PMWS and it doesn't appear that SEW can bring the disease under control. Some benefit has been reported from adopting strict AIAO policies and rigorous sanitation. This may also explain some of the differences seen with Europe, since farms there tend to be continuous flow operations. Controlling or eradicating the PRRS infection may be the only strategy available to bring some measure of control to PMWS.

Salmonellosis

An infrequent problem in modern, high-health farms, salmonellosis, due to Salmonella cholerasuis (S. cholerasuis), can result in respiratory distress and pulmonary lesions. S. cholerasuis is a systemic organism, producing lesions in a variety of organs, including spleen, kidneys and lymph nodes (enlarged and hemorrhagic). In the lung, a patchy pneumonia can frequently be seen, with the pneumonic areas distributed throughout the lung, instead of in the anterior portions as seen in other bacterial pneumonias.

S. cholerasuis responds to some systemic antibiotic treatments. But since the organism can infect humans, there is considerable debate as to whether antibiotics should be provided. Some live, avirulent vaccines have recently been licensed for this disease. These are quite effective and represent a better option to managing the disease.

Other recommendations include improving sanitation and the use of meal feed instead of pellets. However, it is unclear how much these strategies, which are successful in controlling the non-systemic salmonella of the pig, are actually effective with S. cholerasuis.

Researcher Urges Renewed Efforts to Deal with PRRS

Leading PRRS (porcine reproductive and respiratory syndrome) researcher Scott Dee, DVM, says the swine veterinary community needs an awakening and refocusing toward the goal of PRRS control and eradication.

“Veterinarians in North America and Europe possess some incredible diagnostic tools, such as molecular sequencing, that are unavailable in other countries,” states Dee, associate professor, University of Minnesota College of Veterinary Medicine.

Instead of using that technology to make much progress against PRRS, veterinarians, scientists and industry partners have taken to arguing amongst themselves. This needs to stop, and the industry needs to get on the same wavelength to identify the problems and develop solutions to PRRS issues, he asserts.

In short, the industry needs to redouble efforts to clean up PRRS, notes Dee. Realize, however, that there is no single blanket program that will work for PRRS eradication.

However, if there are multiple, diverse genetic strains of PRRS present in a herd, it's doubtful that gilt acclimation or vaccination will work. “Eradication may be the best solution,” he says.

In a talk at the Leman Swine Conference in Minneapolis, Dee outlined his concerns regarding the current status of PRRS eradication.

  • There is a great deal of confusion in the pork industry as to what exactly constitutes a PRRS negative herd. Breeding herds should not be considered negative based on production of negative pigs, particularly if 1-2% of groups test positive for PRRS on ELISA (enzyme-linked immunosorbent assay) test. What's needed is a global standard for a “PRRS-naïve” farm, a farm that has truly never been exposed to the PRRS virus since its inception.

  • There is no need for sale of PRRS-positive breeding stock in the pork industry today. The defeatist attitude that says there are two kinds of herds in the industry today — those that are going to get PRRS and those that have it — has done much to blunt progress of PRRS cleanup. Dee says producers don't have to live with PRRS. There is no need to buy the disease, either.

    He declares: “Producers should always insist on PRRS-naïve semen and replacement stock, and have quarantine and testing programs in place to validate this status when new genetics arrive.”

  • Production of negative pigs from PRRS-positive sows is no guarantee of negative herd status.

  • There is no universal PRRS eradication program. As has been aptly demonstrated in the pseudorabies eradication campaign, multiple eradication schemes need to be developed and the correct one tailored to fit individual operations. Veterinarians should assess all options to select the correct means of eliminating PRRS from a particular farm. The strategy selected should be based on the level of risk that the veterinarian and the producer are willing to accept, capital available and if there are alternate sites.

    Rollover programs hold promise but need further evaluation. Test and removal programs work very well for unvaccinated farms. Depopulation-repopulation remains a viable option; however, reinfection is a major risk factor to consider, says Dee.

  • Avoid drawing conclusive findings from limited data on sentinel animals. Negative status means simply that the tested animals have not been infected. It does not indicate anything regarding the carrier status of the herd. Testing isolated gilt sentinels can produce “false negative” readings. Remember that breeding stock can carry PRRS virus and not shed.

    “Therefore, based on data from our sow model and shedding experiments, I believe the best solution is to use PRRS-naïve, vasectomized boars as sentinels, housing them adjacent to pens of weaned sows, allowing for nose-to-nose contact on a daily basis.” This recommendation is based on an increasing number of cases where gilt sentinels housed in gestation have remained negative, yet sentinel boars in contact with weaned sows in the breeding area have become positive (seroconverted) for the virus.

  • Quibbling and arguing amongst veterinarians has reduced the stature of the profession. What's needed is unification so we can speak with a common voice regarding PRRS, he points out.

    “Only if we work together will we win the war against this very clever virus,” concludes Dee.