Mycoplasma continues to be a significant pathogen even as the pork industry moves toward high-health production. It reduces average daily gain and full-value slaughter pigs and decreases feed efficiency.
Historically, the pneumonia is characterized by respiratory signs in mid- to late-nursery stage. However, the disease has changed in recent years to a more severe and later-finishing presentation. Coughing commonly begins at 10 to 12 weeks of age and occurs three to four weeks after the initial infection. As the concentration of the organism reaches a threshold within the pig or population, a chronic, non-productive cough occurs.
Mycoplasma is not invasive and is found attached to the respiratory epithelium (membrane tissue). The organism is most often a co-infection with other viral pathogens, including porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV) and porcine circovirus type 2 (PCV2); or bacterial pathogens, including Pasteurella multocida and Haemophilus parasuis.
Mycoplasma is transferred by aerosol or by direct pig-to-pig contact. The organism typically transfers from older to younger pigs and from dam to piglet during lactation. All ages are equally susceptible. Spread is slow.
With segregated production (off-site weaning), there is considerable variation between groups as to the level of disease severity. The goal is to reach market weight without clinical signs and lesions.
Vertical transmission (sow to pig) is influenced by herd parity distribution and the infection activity in the sow herd. These two factors vary with each farrowing group and produces variation of weaned pig prevalence.
Often, replacement gilts are mycoplasma-negative, and routine vaccination prior to entry doesn't completely protect against infection, so replacement rates and mycoplasma status at entry add to variation in weaned pig prevalence.
Necropsies, serology and nested polymerase chain reaction (PCR) assays are widely used for diagnosis. Serology has its limitations because seroconversion from natural infections is delayed. PCR is frequently used to detect mycoplasma from nasal swabs, offering the advantage of detecting the organism from live animals, determining prevalence and identifying the age that pigs will develop clinical signs.
Vaccination and/or vaccination with strategic inclusion of feed-grade antibiotics control clinical disease. Vaccines are labeled as a one- or two-dose product. The immune protection is thought to be through cell-mediated response and provides no correlation between serum antibody level and protection. Typical vaccine timing is to give the single dose or the first dose of a two-dose product at 21 days of age (weaning). The second dose of a two-dose regimen is given 2-3 weeks later at 5-6 weeks of age. However, there are advantages to administering mycoplasma vaccine to suckling pigs:
There is typically higher compliance with suckling pig vaccination, as each individual pig is handled compared to a wean-to-finish or nursery population in which individual piglets are normally not handled.
Vaccination of suckling pigs prevents administration of vaccine when there is PRRS, PCV2 or SIV circulation at 3-8 weeks of age. Administration of any vaccine when pigs are PRRS or PCV2 viremic will transfer the viruses, and thus more rapidly infect the population.
Vaccination occurs before mycoplasma prevalence increases if there is activity in sows. Suckling pig vaccination should also be considered if there is vaccine interference with maternal antibodies that pigs would acquire from colostrum. The duration of immunity of the vaccine must also be sufficient to protect the pig to market.
Studies have shown differing results as to whether pigs can be vaccinated in the presence of maternal antibodies. But it is generally accepted that pigs can be effectively vaccinated in the presence of maternal antibodies.
A University of Minnesota study indicates that pigs have memory cells from their dam, and if stimulated when very young, can respond successfully to mycoplasma vaccination.