The American Association of Swine Veterinarians’ (AASV) Porcine Circovirus Associated Diseases (PCVAD) committee met during the World Pork Expo in Des Moines, IA last week.
The newly-formed committee, chaired by AASV past-president Dr. Tom Gillespie, held its first meeting on Thursday morning to discuss the latest updates on the disease progression in North America and Europe, vaccine issues, case definitions, research topics and database surveillance tools. Information provided by those in attendance indicates that PCVAD is severe in certain herds and production flows in concentrated pockets in hog dense areas of the U.S. The syndrome typically affects pigs in the early to mid-finisher. Reports from the field and the research lab indicate that the pigs that survive do not show reductions in growth rates and that it is not uncommon to observe a single pig in a pen exhibiting clinical signs.
Dr. Joaquin Becerril and Dr. John Harding gave similar reports regarding the current status of the disease in Mexico and Canada respectively. Dr. Becerril reported that the first case was reported in Mexico in 2001 and currently there is a significant outbreak in northwestern Mexico. Dr. Harding reported findings from a study which evaluated the differences in RFLP patterns between PCVAD clinically-affected and clinically-unaffected farms in Canada. The virus isolated from a majority of the clinically-affected farms was identified as having a 321 RFLP pattern vs. the 422 RFLP cut pattern observed on a majority of the clinically-unaffected farms (2006, unpublished).
There was a lot of discussion about strain variation and its significance relative to virulence and vaccine efficacy. The group expressed concern about the ability of current PCR tests to detect different strains and the apparent link between the severe outbreaks currently being observed and a strain isolated in France. Practitioners were cautioned about making inferences regarding vaccine selection based on genetic analysis of the virus. At this point, the viral genotype implications are not well understood.
The committee also discussed anecdotal reports regarding vaccine efficacy following field use in the U.S., Canada and Europe. Currently, three commercial vaccines are available on the global market. Some committee members emphasized that pigs from vaccinated or naturally-infected sows would likely have significant maternal antibodies that may block development of active immunity. They stressed the importance of vaccinating piglets following maternal antibody decline.
The group also finalized a PCVAD case definition which will be submitted to the AASV board of directors for approval at their fall meeting and reviewed a disease mapping tool being developed at Purdue University. This tool would facilitate the detection and tracking of disease or syndromic outbreaks and could aid with research efforts exploring viral transmission within and between farms. If you would like to contribute herd data to this confidential database please visit their website at http://web.ics.purdue.edu/~helmelee/swine/survey.php and complete a short questionnaire.