Comparing Circovirus Vaccine Efficacy

Most hog operations with porcine circovirus type 2 (PCV2) also have a multitude of co-infections, namely porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV) and Mycoplasmal pneumonia. But clearly, PCV2 alone can dramatically impact mortality, morbidity, percentage marketed and average daily gain. Joe Connor, DVM, co-owner of Carthage (IL) Veterinary Service, Ltd., estimates

Most hog operations with porcine circovirus type 2 (PCV2) also have a multitude of co-infections, namely porcine reproductive and respiratory syndrome (PRRS), swine influenza virus (SIV) and Mycoplasmal pneumonia. But clearly, PCV2 alone can dramatically impact mortality, morbidity, percentage marketed and average daily gain.

Joe Connor, DVM, co-owner of Carthage (IL) Veterinary Service, Ltd., estimates that the federally approved circovirus vaccines provide a return on investment (ROI) of 6:1 to 8:1 in herds with co-infections, based on Kansas State research.

He presented results of a wean-to-finish trial at a World Pork Expo seminar, sponsored by Fort Dodge Animal Health, in a herd naturally infected with PCV2, but free of PRRS and SIV and stable for mycoplasma. The PCV2 vaccines yielded a 3:1 ROI.

“When it comes to cutting costs, circovirus vaccines are way down the list because response to infection is huge,” Connor comments. “There is a tremendous improvement in performance. Vaccines capture a lot of pounds and provide a return that is quite high compared to other interventions.”

Vaccine Trials

The 141-day trial ran from November 2007 to March 2008. A total of 1,200 weaned pigs were fed out in a typical, totally slotted, tunnel-ventilated, wean-to-finish barn featuring 40 pens, 30 pigs/pen at 7.5 sq. ft./pig.

The barn had a history of PCV2 infections; mortality six months ago was 27%.

The six treatment groups were:

  • Suvaxyn PCV2 One Dose (Fort Dodge Animal Health) given at 3 weeks of age;

  • Suvaxyn PCV2 One Dose administered at 5 weeks of age;

  • Performance Results

    Suvaxyn PCV2 One Dose given as a split dose at 3 and 5 weeks of age;

  • Ingelvac CircoFLEX (Boehringer Ingelheim Vetmedica, Inc.) given at 3 weeks of age;

  • Circumvent PCV (Intervet), a two-dose vaccine, administered at 3 and 5 weeks of age; and

  • Control pigs given sterile water injections at 3 and 5 weeks of age.

Twenty-five percent of the pigs that were randomly tested by serology at seven different intervals to determine antibody response and polymerase chain reaction (PCR) tests were analyzed for the age of pig infected with PCV2, length of PCV2 viremia (infection in the blood) and the PCV2 strain.

Connor says all three vaccines showed nearly equal efficacy “in mitigating clinical signs, but also reducing the amount of virus present and reducing the duration of shedding of the virus.”

Total Mortality Regardless of Cause of Death
Figure 1. Total Mortality Regardless of Cause of Death
Select image to enlarge

Figure 1 (page 26) illustrates what Connor refers to as the “clustering effect” of vaccinated pigs vs. control group pigs for impact on mortality. Suvaxyn One Dose given at 3 weeks of age led the pack with 1.0% mortality, followed by Intervet's Circumvent PCV with 2.0% mortality.

For morbidity rates, based on total pigs culled that were under 200 lb. (Figure 2), vaccine results were again similar. Suvaxyn's One Dose given at 5 weeks of age led with 0.5% morbidity.

Illinois Herd Beats Circovirus

All five groups of vaccinates showed marked results in finishing close to 95% of pigs on test, compared with 88% of control pigs.

The serological summary indicated an excellent response to vaccination. PCRs indicated excellent natural PCV2 virus infection in controls and much more rapid clearing of the virus in vaccinated pigs. The differential PCR tests indicated that both PCV2a and PCV2b strains were present with PCV2b the most prevalent strain.

Connor stresses that as good as the vaccines are in beating down PCVAD (porcine circovirus-associated disease), the industry is challenged in keeping PCV2 out of the building environment to prevent reinfection. He says sanitation and hygiene and all-in, all-out pig flows should still be the hallmark of biosecurity programs.

Total Culls/Morbidity
Figure 2. Total Culls/Morbidity
Select image to enlarge

Some pigs clear the virus relatively slowly, leaving “seeders” to contaminate facilities for the next group.

PCV2-viremic pigs can increase difficulty of disease control because the hardy virus can be shed and easily live in barns/farms and transport trucks.

Pike Pig Systems of Pike County, IL, is a 1,400-sow, farrow-to-finish operation that dealt with the usual disease suspects from 1995 to 2005, says herd veterinarian Patrick Graham, Ghrist Veterinary Clinic, Pittsfield, IL.

There were two major cases of porcine reproductive and respiratory syndrome (PRRS) during that decade, and two or three outbreaks of swine influenza virus.

Back then the operation targeted production at 600 pigs/week. Pigs flowed into eight, 600-head nursery rooms and then into nine, 1,200-head finisher barns. The nurseries and finishers were just 600 yards apart, and both were continuous-flow systems, Graham says.

Along the way, the herd also dealt with ileitis, Mycoplasmal pneumonia, erysipelas and circovirus.

In 2005, additional losses were due to vaccine failures for PRRS and mycoplasma and lack of response following antibiotic treatments. Clinical disease signs slowly worsened. Progressively, respiratory and enteric problems increased, and culls and death losses became elevated.

Diagnostics provided a clearer picture of herd health. PRRS, mycoplasma, Haemophilus parasuis and Actinobacillus suis were all identified; porcine circovirus type 2 (PCV2) and ileitis were questioned as factors. An aggressive antibiotic program failed.

Poor-doing pigs were aggressively sorted off, and many that failed to thrive were euthanized. In characterizing the herd, Graham says: “The good ones were good, but the bad ones were bad!”

Nursery performance was generally unaffected, while finisher performance crashed. Death loss rose over a four-week period in early finishing with prolonged periods of scours, wasting and porcine dermatitis and nephropathy syndrome.

During the fall of 2005 through the first two months of 2006, prior to implementing a circovirus vaccination program (Circumvent PCV from Intervet/Schering-Plough Animal Health), mortality bounced around from 5-15%, Graham notes. Again there were finisher pigs that did quite well — with average daily gains nearing 2 lb./day and feed conversion rates of less than 3:1.

In March 2006, PRRS vaccination was stopped and circovirus vaccination was started. The mortality rate for 2007 dropped to 3.8%. From March 2006 to April 2007, performance rebounded with an average daily gain of 1.92 lb./day and an average feed conversion rate of 2.89.

Graham says vaccines worked and antibiotics didn't in controlling PCV2-related diseases. With medication, control costs were $132.06/head and death loss was 17.1%. With vaccination, death loss dropped to 2% and costs ran $117.51/head. As a result, Pike Pig Systems reconfigured their hog operation, producing 1,300 pigs/week and contract finishing.

“Circumvent PCV dramatically improved performance, and when pigs are vaccinated at the right time — at 3 and 5 weeks of age (two-dose vaccine) — the vaccine is highly cost-effective,” explains Graham.
— Joe Vansickle

Subclinical Circovirus Can Still Hurt Performance

If you think circovirus is not harming pig performance because you do not see active signs of the disease, and mortality rates have not really spiked, you might want to think again.

That's the view of Doug King, DVM, Cargill Pork, based in Wichita, KS, who learned that a mild clinical presentation could be hiding performance losses.

Normally, porcine circovirus type 2 (PCV2) strikes pigs at 6 to 18 weeks of age, producing a plethora of clinical signs, often resulting in emaciation and death.

Case Study

A three-site production system was negative for porcine reproductive and respiratory syndrome, but positive for Mycoplasmal pneumonia and PCV2. Pig viremia (virus infection in the blood) peaked when pigs were around 10 weeks of age — but there were no clinical signs of disease, King explained in a talk at World Pork Expo.

To find out if subclinical PCVAD (no visible signs) was having an impact on performance and the company's bottom line, King designed a trial where 1,200, 21-day-old weaned pigs were commingled at the nursery and placed in two groups. Half of the pigs were vaccinated at 3 weeks of age with Boehringer Ingelheim's CircoFLEX, while the other half were unvaccinated and served as the control group. Vaccinates and controls were commingled with either 25 or 50 pigs/pen. Pigs were weighed on the day of vaccination (Day 0), Day 41 and on Day 131 at the end of the trial.

All of the pigs remained clinically normal throughout the trial, even though PCVAD was confirmed by tissue analysis in individual pigs.

Results showed that vaccinated pigs had significantly reduced PCV2 viral loads at 10, 14 and 18 weeks post-placement.

According to King, there were no differences between the two treatment groups for average daily gain (ADG) during the nursery phase (Day 0-41).

But pigs vaccinated with Ingelvac CircoFLEX showed better ADG (1.92 lb./day) from Day 41 to 131 vs. 1.85 lb./day for control pigs. Overall, ADG for Day 0-131 was 1.57 lb./day for vaccinates vs. 1.52 lb./day for controls (0.06 vaccinate ADG advantage).

Although King says there were no major differences during the study for either nursery or finishing mortality rates, test results indicated a significant reduction in the number of bottom-end pigs in the vaccinated group. At Day 131, 5.16% of vaccinates weighed less than 180 lb., vs. 10.24% that weighed less than 180 lb. in the non-vaccinated group. Combined nursery and finishing scores did show some overall differences in mortality rates at 5.18% for vaccinates vs. 7.07% for non-vaccinates.

“Pigs vaccinated with Ingelvac CircoFLEX had heavier average hot carcass weights and a more muscular carcass,” he notes. Vaccinate hot carcass weights averaged 194.23 lb., while control hot carcass weights averaged 190.76 lb.

As far as total weight differences, vaccinates in the trial produced 5,805 lb. more pork than controls (140,784 lb. vs. 134,979 lb.).

King calculated the total market value (including culls) of vaccinates and controls by factoring in additional revenue based on the packer market grid matrix. Vaccinates earned about a 1% premium in value relative to the control pigs.

“From those values, one can conservatively estimate a $4.38 return on investment for every dollar invested in Ingelvac CircoFlex vaccine in this study,” he says.

King concludes the addition of vaccine to this production system upgraded key production parameters unrelated to any impact on mortality, providing evidence that vaccination can play a major role in controlling the subclinical impact of PCV2.
— Joe Vansickle