PCVD, PRRS and swine influenza dominate the Barcelona conference on pig diseases

Monday, February 20, 2012

With 113 papers delivered, PCV2 was the top topic at last June's symposium on Emerging and Re-Emerging Pig Diseases, with PRRS not far behind 

by S. ERNEST SANFORD

The 6th International Symposium on Emerging and Re-emerging Pig Diseases took place in Barcelona, Spain, on June 12-15, 2011. Just over 1,000 participants attended the conference, which had 250 oral and poster presentations, in addition to keynote lectures on porcine circovirus type 2 (PCV2), PRRS and influenza viruses. PCV2 (113 papers) was the top topic again, as it has been for the last three Emerging Diseases symposia, followed by PRRS (71) and various emerging and re-emerging diseases (66).

Emerging Swine Diseases

Dr. X. J. Meng of Virginia gave an overview of emerging viral diseases in swine. The list is long and only partial, but it includes several that can cross over to humans. Many of these viruses have emerged in the last two decades. A few names are familiar, many are not. Most, however, are of great concern because of their zoonotic potential, meaning they can jump from the pig and infect humans.

Here are a few of these new emerging viruses:
- Swine hepatitis E virus (SHEV)
- Torque teno sus virus (formerly Torque tenovirus)
- Porcine boca virus (PBoV)
- Porcine lymphtrophic herpesvirus (PLHV)
- Porcine torovirus (PToV)
- Porcine sapovirus (PSaV)

Most of these viruses are nonpathogenic in swine or their pathogenicity is unknown.

They also cannot be cultured, so they have all been identified by polymerase chain reaction (PCR). SHEV and PLHV are of definite zoonotic concern. The others are potential zoonoses.

Porcine Circovirus type 2 (PCV2)
Here are synopses of a few of the PCV2 papers presented as oral presentations or posters.

A study in Spain of the age at onset of PCV2 infection detected by antibody response to PCV2 virus
– Jiminez M, et al. Pg 44.
Background. Some 10,595 serological cross-sectional samples from pigs in 294 unvaccinated herds analyzed at various Spanish laboratories between 2008-2010 were used in this study. The commercial Circovirus Ingezim IgG/IgM kits were used for the serological tests.

Results. From Table 1, it can be seen that the average age of onset of PCV2 infection over the three-year period investigated occurred from about 12 weeks of age or older, a post-nursery age period thus indicating an older age of onset of PCV2. This is pertinent because the history of PCVD in Europe is that it was a nursery pig disease, whereas in North America it has been a finisher pig disease.

Take Home. More than 80 per cent of herds are infected between nine and 16 weeks of age. Early infections are not frequent. Late infections (more than 16 weeks of age) occurred in more than 10 per cent of the herds.

Impact of maternally derived immunity and early PCV2 viremia in a U.K. commercial herd
– Hayden J, et al. Pg 46.
Background. The study was conducted in a 250-sow, three-week batch farrow, farrow-to-finish, PRRSV and Mycoplasma hyopneumoniae-negative herd to determine if maternally derived antibodies (MDAs) prevent piglet viremia.

Results. Ten of 112 (11 per cent) piglets were PCR-positive for PCV2 at weaning. Body weight was significantly correlated with weaning and grower weight, but didn't affect viremia at weaning. There was significant correlation between PCV2 antibodies (Abs) in colostrum and PCV2 Abs at weaning (p<0.001). Piglets viremic at weaning had significantly lower Abs at weaning (p<0.01) than nonviremic piglets. Pigs born from sows with high Ab levels in colostrum had significantly higher Ab levels at weaning and piglets with lower Ab levels at weaning were more likely to be viremic (p<0.001). Weaning weight of piglets with and without viremia was 6.7 kilograms and 7.7 kilograms, 38.2 kilograms and 41.0 kilograms at 27 and 82 days of age, respectively.

Take Home. Passive immunity reduces neonatal viral replication and provides protection to piglets.

There was a positive correlation between PCV2 Ab levels in colostrum and Abs at weaning.

Piglets with viremia had significantly less PCV2 Abs at weaning than piglets without viremia.

Piglets with poor passive immunity and born from sows with low Abs in colostrum are at higher risk of early viremia.

Investigation of PCV2 status in Danish herds – One-year longitudinal study
 – Kristensen CS, et al. Pg 104.
Background. 2003: A serological survey conducted in Danish herds showed more than 90 per cent of herds positive for PCV2.

2009: The survey was repeated in 2009 and showed only 72 per cent of herds were PCV2-positive. Were herds becoming PCV2-free? Or was this reduction in percentage of PCV2 positive herds due to fluctuations in PCV2 positive levels within herds? To answer this question, eight herds were retested. Two of the retested herds were still PCV2-negative.

2010: A more intensive investigation was conducted in these 2 PCV2-negative herds. Eight weekly serum samples from the two herds were analyzed by PCR for PCV2. In Herd 1, a PCV2-vaccinated (Ingelvac CircoFLEX®) farrow-to-finish sow herd, each weekly batch of weaned piglets was vaccinated with the same PCV2 vaccine, except one batch in May 2010. Herd 2 was a farrow-to-finish sow herd with no PCV2 vaccination of sows or piglets.

Results. Herd 1: All samples were PCR-positive for PCV2 except samples from the one unvaccinated batch in May 2010. Herd 2: The first two (of eight) weekly samples were negative for PCV2 by PCR. The last six weeks' samples were PCV2 positive.

Take Home. These herds were not PCV2 free. Fluctuations of PCV2 viral levels occur in herds over time. PCV2 vaccination can reduce PCV2 infection to levels below detection limits of the PCV2 PCR test.

PCV2 virological profiles in PCVD affected and non-affected herds
– Lopez-Rodriguez A, et al. Pg 105.
Background. The researchers compared PCV2 viral loads in feces and Ab profiles of pigs from PCVD affected (PCVD AH) and non-affected herds (PCVD NH). Feces and serological profiles were examined for PCV2 from 10 PCVD AH and 10 PCVD NH herds. The PCVD AH herds had at least one nursery pig diagnosed with PCVD.

Results and Take Home. There were no significant differences in serological profiles in PCVD AH and PCVD NH herds. PCVD AH herds, however, had a higher average percentage of PCV2 in feces for pigs at 9, 15 and 21 weeks of age. High amounts of PCV2 in feces in pens could be an indicator for PCVD in herds.

Use of the new BacuCheck™ ELISA to differentiate between PCV2-vaccinated and unvaccinated pigs of different ages
– Ladinig A, et al. Pg 122.
Background. BacuCheck™ ELISA is a new ELISA kit to detect Abs to the baculovirus used in production of Porcilis PCV vaccine. It differentiates between vaccinated and unvaccinated pigs. In this study, 40 pigs were placed in two groups; 20 vaccinated with Porcilis PCV and 20 left unvaccinated.

Results and Take Home. BacuCheck™ ELISA identified vaccinated pigs from seven weeks of age.

BacuCheck™ ELISA also identified unvaccinated pigs from 14 weeks of age (i.e. as vaccinated pigs).

The recommendation of the company is not to use BacuCheck™ ELISA in pigs older than 12 weeks of age.

Reproductive failure caused by PCV2 infection and field experiences with PCV2 sow vaccination
– Diaz E, et al. Pg 149.
Background. A 3,000-sow, three-site production herd experienced PCVAD in late 2007. PCV2 vaccination (Ingelvac CircoFLEX) of three-week-old piglets was instituted. Pre-PCVAD piglet mortality was 4.2 per cent and increased to 12 per cent during PCVAD, then dropped to 3.6 per cent after PCV2 vaccination.

In 2009, reproductive PCVAD was confirmed by PCV2-positive strains in 20 of 28 aborted fetuses. Mass vaccination of all breeding animals (gilts, sows, boars) commenced in June 2009. Thereafter, gilts which had been previously vaccinated as three-week-old piglets were revaccinated at 21-22 weeks of age. Then all gilts and sows continued to be vaccinated at five weeks pre-farrowing.

Results. Since October 2009, all pigs have been PCV2-negative by PCR.  All mummies and aborted fetuses have tested PCV2-negative (Table 1).

Take Home. Sow vaccination seems to have controlled the PCV2 reproductive problems.

Revealing of suspected vaccination fraud using serological tools
–  Lindahl E, et al. Pg 178.
Background. An owner of seven finisher farms, each with 8,600 places, buys in 1,100 pigs, averaging about 30 kilograms (10 weeks old) from an external sow herd and places them with 260 pigs from his own farm every three weeks. Pigs are placed in the same finisher barn but bought-in pigs and home pigs are placed in separate rooms. Both groups of pigs are supposed to be vaccinated with Ingelvac CircoFLEX.

In spring of 2010, it became obvious that the two groups were performing differently.

Mortality in the purchased pigs was four to seven per cent, substantially higher than the home-sourced pigs (1.6-2.2 per cent). Furthermore, growth rates were vastly different. At 16 weeks post-placement, the home-sourced pigs had all been marketed, whereas most of the purchased pigs were not yet marketed with a significant number still on-farm at 18 weeks post-placement. A diagnostic investigation was launched. Four batches of purchased pigs and five batches of home pigs were bled and five bloods from each batch were tested with Ingezim Circovirus AgG/IgM ELISA. From each batch, the five samples were pooled and tested by qPCR for PCV2.

Results. Viral loads were much higher in bought batches compared to home batches. There was no IgM response in home batches, whereas 80-100 per cent of bought batches had IgM titres. Both groups had IgG responses.

On questioning, the supplier claimed he had vaccinated his pigs with Circovac, not CircoFLEX. The diagnostics, however, proved conclusively that the pigs had never been vaccinated with any circovirus vaccine, since they all had IgM titres which could only have happened if they had come in contact with PCV2 recently and not months ago (i.e. when vaccinated at weaning) as the home pigs showed.

Conclusion. This was a case of vaccination fraud. The pigs had never been vaccinated.
PRRS Papers

Use of air filtration as a means of reducing the frequency of PRRSV infections in large breeding herds in swine dense regions
– Dee S, et al. Pg 64.
Background. Filtering of sow barns is now recognized as a significant component to prevent aerosol PRRSV infection of sow herds. A study was conducted over a 30-month period (September 2008-February 2010) comparing 10 filtered sow herds with 30 unfiltered control herds.

Results. In eight filtered herds there were no PRRS breaks. Two filtered herds broke with PRRS. Breaches in transport and personnel biosecurity were identified in both breaks
Of 30 unfiltered control herds, 28 had PRRS breaks in the same time period; 17 (62 per cent) herds broke once; seven (25 per cent) herds broke twice; and four (13 per cent) herds broke thrice.

Take Home. Sow herds in filtered barns are less likely to break with PRRS (p<0.0001).

PRRSV enhances PCV2a and PCV2b replication and duration of shedding
–  Opriessnig T, et al. Pg 41.
Background. A study was conducted to determine the impact of PRRS virus on replication and shedding of PCV2a and PCV2b.  Two- to six-week-old, PCV2 and PRRSV-naïve pigs were challenged with PRRS virus and PCV2a or PCV2b, separately and in combination. Suitable controls were maintained.

Results. Significantly higher quantities of PCV2a and PCV2b DNA were found in tissues of pigs concurrently infected with PCV2 and PRRS virus compared with pigs singularly infected with PCV2.

Take Home. PRRS virus enhances the replication of PCV2. There is no difference in the shedding patterns between PCV2a and PCV2b. This highlights the importance of controlling PRRS virus infection to reduce PCV2 loads in pig populations.

Swine Influenza Papers

Dynamics of influenza transmission in vaccinated and non-vaccinated pig populations
– Torremorell M, et al. Pg 78.
Take Home. Swine influenza virus (SIV) vaccines can decrease transmission of SIV, but they also contribute to maintaining endemic infections, especially when vaccine strains differ from the circulating SIV strain.

The impact of maternally derived antibodies on transmission of SIV in neonatal pig populations
– Allerson M, et al. Pg 260.
Background. Sows were vaccinated with: a homologous H1N1 SIV vaccine; a heterologous H1N1 SIV vaccine; or not vaccinated.

Ten offspring, three to four weeks old, from each of the three groups of sows were challenged with SIV via nose-to-nose contact with an experimentally infected pig introduced into each group.

Results. All contact pigs became infected within six days of contact with the introduced infected pig regardless of treatment group. Timing and duration of infection post-challenge differed between groups.

Take Home. Vaccine-induced immunity may not prevent transmission of SIV in pig populations.

The Emerging and Re-emerging Pig Diseases Symposia have now settled into a rotation of having conferences every four years – in the year in between the International Pig Veterinary Society Congresses. The last five have been in Europe, but the next one in 2015 will be in Japan. PCVD, PRRS and swine influenza continue to dominate this conference. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com