An Update On The U.S. National Porcine Circovirus Type 2 Prevalence: Before And After Wide Scale Vaccination

Porcine circovirus 2 (PCV2) is associated with Porcine Circovirus Associated Diseases (PCVAD), such as a syndrome causing weight loss and ill thrift. PCVAD threatened the swine industry in Europe and later North America for about 15 years. In North America PCV2 vaccines were introduced in 2006. Since then four vaccines have come into widespread use. However, there has been little research to determine whether wild virus is still circulating in the national herd, whether U.S. swine producers still observe clinical signs suggestive of PCVAD or whether the relative prevalence of the two main genotypes of PCV2(PCV2a and PCV2b) has changed in the intervening years.

Questionnaire data and blood samples were collected as part of the NAHMS Swine 2006 and 2012 studies. In 2006, blood samples were collected from up to 35 grower/finisher market pigs per farms on 185 farms in 16 states. A Capsid based ELISA was used to test for the presence of PCV2 antibodies and a TaqMan (TM) quantitative PCR was used to test whether PCV2 DNA was present in the sera of these pigs. A SYBR Green (SG) dye-binding PCR combined with melting point analysis was used to detect PCV2 genotype in sera.

In 2012, blood samples were collected from up to 17 grower/finisher market pigs per farm on 137 farms in 10 states. Capsid and Replicase based ELISAs were used to test for the presence of PCV2 antibodies to vaccine and wild type virus, respectively. SG quantitative PCR alone was used with melting point analysis to detect DNA presence and genotype.

Per the questionnaire data, nationally, 31.3% and 13.7% of sites with grower/finisher pigs reported PCVAD in 2006 and 2012, respectively. The farm level prevalence for exposure (PCV2 antibodies) across years ranged from 98.9 to 100%. The Capsid ELISA from 2006 and the Replicase ELISA used in 2012 assessed whether pigs had been exposed to wild type PCV2 virus. Both tests revealed approximately 78% of animals had been exposed to virus. Nearly 83% of animals and 100% of farms sampled were infected (per PCR) with PCV2 in 2006. In 2012, less than 18% of animals and 47.9% of farms were infected. There has been a shift away from infections with PCV2a and mixed infections towards PCV2b infections between study years.

Prior to the use of vaccines, more farms with weaned pigs reported clinical signs of PCVAD. However, the disease remains as does exposure to wild virus. The reason for the apparent reduction in animal level infection in 2012 is likely due to vaccination and subsequent viral clearance. The shift in genotype profile may reflect a greater ability for PCV2b to out compete PCV2a.

Disclosure of Interest: None Declared.