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Genetics, environment, management practices, stress and other infectious diseases are all factors that must be taken into account when facing PCVAD in a production system, points out François Cardinal, DVM, Drummondville, Quebec.

“In my opinion, other diseases are the most important factor since they can trigger expression of PCVAD or increase losses as secondary infections of immunocompromised pigs,” he said during the March 2008 AASV meeting.

Porcine reproductive and respiratory syndrome (PRRS) is probably the most important cofactor disease to consider because its presence has the ability to double the mortality caused by PCVAD, says Cardinal.

Many researchers have emphasized the importance of maternally derived immunity in providing some protection to piglets facing the disease. There is also evidence that piglets may be infected in-utero and act as a source of virus for their cross-fostered littermates.2

The complexity of PCVAD is not only related to its multifactorial nature, but also to the fact that PCV2 infection, immune status of the pig and stressors from other infections must occur at a determined moment in time, in order to cause the disease.

This means that the practitioner has to be extremely vigilant with respect to the chronology of the significant events in the life of a pig in order to understand the course of the disease in a particular herd, continues the Canadian practitioner.

Finally, in comparison to disease agents such as PRRS virus, PCV2 appears to be more resistant to both extreme environmental conditions and various disinfectants. It is therefore even more important that sanitation protocols be adapted to this new challenge and reinforced with staff so that compliance with the protocols is improved.

Commercial PCV2 vaccines are, by far, the single-most effective tools currently available for control of PCVAD, notes Cardinal. “However, I think that we must not allow the effectiveness of PCV2 vaccines to cause us as practitioners to be complacent about the role of good management practices and long-term strategic planning. We must not allow vaccination to become a substitute for good management practices.”

Another very important aspect in the prevention of PCVAD is the control of other diseases and pathogens. PRRS is the top priority, but Mycoplasma hyopneumoniae, swine influenza virus and salmonellosis also are important, says Cardinal.

Working on optimizing pig flows, designing and validating of acclimatization protocols, improving biosecurity measures and adapting vaccination regimens are key components in a systematic approach to the prevention of these major disease pathogens. Three-site systems that have managed to limit piglet, litter and pen mixing, all the way from birth to slaughter, have been able to significantly decrease mortality rate.

“Reduction of disease transmission between herds is a long-term objective that we have collectively tried to address in Quebec,” he says. “We are actually working on a regional approach that, we hope, will allow for tracking disease transmission between herds, promote the implementation of effective on-farm and off-farm biosecurity protocols, take into account principles of regional transmission of diseases in the establishment of new pig farms and eventually eradicate PRRS from some regions.

“This plan focuses mainly on PRRS because we are convinced that PCVAD losses would not have been as severe in Quebec if more herds had been free of PRRS virus at the time of the PCVAD epizootic.”

It is also believed that the widespread presence of PRRS may provide a similar “amplifying effect” for the next emerging disease that will affect the swine industry, continues Cardinal. This strategy is then aimed to control diseases other than PCVAD but at the regional level instead of at the herd level.

Before PCV2 vaccines were available, PCVAD was a huge challenge for producers, Cardinal concludes. Now that the success of vaccination is bringing some relief, it’s time to look back, to learn and to improve our systems from our new knowledge.

To Vaccinate or Not to Vaccinate: That Is the Gamble Will we vaccinate forever? “It depends,” says Robert Desrosiers, DVM. One determinant is how long there are clinical signs of PCVAD in the absence of vaccination. Last summer, a practitioner who also owns pigs stopped vaccinating them for about three months. His thought was that his pigs were performing very well, and he felt that a significant percentage of this performance was associated with the changes he had made in his management and genetics before he started vaccination. While the practitioner found that losses associated with PCVAD were not as bad as before the changes, they were still too high, and he went back to vaccinating pigs again. In one field study involving four different finishing units, the average mortality rate in vaccinated pigs (half the inventory) was 2.4 percent. Mortality rate for the controls was 9.5 percent. In a second trial, where again half the pigs in one barn were vaccinated and 50 percent kept as controls, the respective mortality rates were 4.6 percent and 14 percent. It may be possible to keep a small percentage of nonvaccinated pigs in a barn and still have meaningful results, although this would need to be properly evaluated if important decisions were to be made based on such field trials.