Farmscape Article 2254  September 23, 2006

The introduction of two new vaccines appears to have turned the tide in the battle to contain a potentially deadly condition that has taken a dramatic toll on swine herds around the world.

Porcine Circo Virus Associated Disease (PCVAD), previously called Post-weaning Multisystemic Wasting Syndrome (PMWS), is a viral disease which typically affects young pigs, weanlings, from eight to 16 weeks of age. However symptoms tend to manifest themselves in the grower phase and the disease is often fatal. The disease was first characterized in western Canada in 1995 and, in the decade since, it has since spread worldwide.

The primary cause has been shown to be a common pathogen, porcine circovirus type 2 (PCV-2), but because this organism is so common, it is believed some additional triggering mechanism is required for the infection to result in symptoms.

Two Vaccines Approved for Use in Canada

Earlier this year two companies were granted emergency licenses to distribute vaccines in Canada and it is hoped two additional products will receive approval within the next 12 months.

One of the two vaccines currently being used in Canada, Circovac, was developed by Merial. The other, as yet unnamed product, was developed by Intervet. Circovac is administered to the sow prior to farrowing to increase the amount of protection passed on from the sow to the piglet in the colostrum. The Intervet product is administered directly to the piglet at the time of weaning, at approximately three to six weeks of age, to stimulate its own immune system making it more able to fight off infection.

Early Evidence Indicates Vaccination Highly Effective

“In North America, or more specifically Canada, it appears we are past the point of crisis,” states Dr. John Harding an associate professor with the Western College of Veterinary Medicine at the University of Saskatchewan in Saskatoon.

“My sources and colleagues in Quebec and Ontario have reported over the last two to three months that there has been a decline in the number of cases and severity of disease. In western Canada it remains a sporadic issue. If anything, the number of cases is probably declining although it still remains quite serious in some particular farms and in the U.S. At this point in time it’s my understanding that we still have discreet areas of the U.S. that are still seeing fairly high levels of clinical disease and quite a concern in some specific areas.”

Dr. Harding suggests, “Circumstantial evidence from the field would certainly suggest that the vaccines are working at this point in time, dropping the incidence down, although I have not seen any hard numbers. We have not seen any data from controlled trials at this point in time but we’re getting very positive feelings from the field.”

Dr. Francois Cardinal, a swine veterinarian with Les Consultants Avi-Porc at Drummondville, Quebec agrees.

He recalls, “If I go back, let’s say, two years ago, PMWS [PCVAD) was not a big concern here in Quebec and it began to be a problem about October of 2004. It increased until summer 2005. When I say increased I mean that more farms were affected and, for the affected farms, mortality was increasing but after 2005, since the winter of 2005 things were improving actually without vaccination.”

Peak Infection Rates in Quebec Believed to be Over 80 Percent

Based on the diagnosis of practicing veterinarians it is estimated that, during the first five months of 2005, between 55 and 60 percent of the finishing sites in Quebec were affected to some degree by PCVAD.

Dr. Cardinal says, “We think, at the peak, we reached more than 80 percent of the farms that were affected at different degrees.”

“The less affected see maybe two or three percent mortality caused by PMWS [PCVAD] so maybe an overall mortality of five percent and the highest I’ve seen is 40 percent mortality but, in those cases with very high mortality patterns, there is always other diseases involved.”

He explains, “The barns where we see 20 percent mortality and more are often affected also with PRRS virus, mycoplasma, flu viruses and other things like that so it's very hard to be clear on what is caused by PMWS [PCVAD] or PCV-2 and what is caused by the other diseases that are present at the same time.”

Vaccination Accelerates Decline in Incidence of PCVAD

However, Dr. Cardinal notes, since the spring of 2006, both the number of affected farms in Quebec and the rates of mortality have decreased and, with the introduction of the new vaccines, the improvement is even better.

He explains, “Just to give you an idea we think that mortality, on average, for the affected farms in Quebec was about ten percent and without vaccination mortality decreased to about eight percent. But now with the vaccine more of the farms are at two or 2.5 percent mortality in finishers.”

Dr. Harding suggests the declines can be attributed to a combination factors.

“One is a tincture of time. If you look at all of the countries globally that have seen an epidemic increase in PMWS [PCVAD], they all naturally tend to decrease over a 24 month period so I think what we’re seeing is partly due to that.”

“With that tincture of time, there are a lot of other things that we probably have intuitively done in the industry, both improving biosecurity, making sure production practices are as good as we can get and obviously controlling as many other diseases as we possibly can so some of those fundamental factors that underlie the PMWS [PCVAD] outbreak have been controlled as well.”

However, he adds, “I think the most significant factor that both is reported from the field and would make some sort of scientific sense would be that we’ve had two vaccines that have now been used in the industry for the last three to six months and I think those vaccines are having a substantial dent in the amount of cases that we have.”

He observes, “Mortality obviously is dropping in some of these most severely affected farms and that’s a real positive.”

Optimism Continues to Build

“We are very optimistic,” says Dr. Cardinal. “We didn’t expect that vaccination would work so well. I can give you an example of farms that were used to seeing 15 or 20 percent mortality in finishers with vaccination decreasing this mortality to two or three percent so it’s a huge improvement.”

Dr. Harding notes, “There will be some controlled studies that report over the next one to two years but we’re hoping that the vaccines actually do their job and PMWS [PCVAD] will decrease in its severity across the country.”

“Really I think the proof will be in the pudding,” he concludes. “We’ll just watch to see how they work in the field.”

Staff Farmscape.Ca