Porcine circovirus 2 (PCV2) is associated with several diseases in pigs including postweaning multisystemic wasting syndrome (PMWS). The virus has been classified into two genetic types of PCV2a and 2b by phylogenetic analysis. Although the PCV2b was commonly associated with PMWS, the genetic groups were not reflected or explained the difference of viral virulence. In an examination of viral characteristics, PCV2 isolates showed unusual resistance in high temperature and low pH. In order to differentiate two PCV2 genotypes, a nested polymerase chain reaction (nPCR) assay was developed. The nPCR was found to be highly specific and sensitive for detecting and differentiating between the two genotypes.
For quantification of the viral load, a real-time PCR assay based on SYBR green was developed for PCV2b and we found that the real-time PCR assay was more sensitive than nPCR and can be a useful diagnostic method for the detection and quantification of PCV2b in swine serum samples. Additionally, a serum neutralization (SN) assay was modified and standardized based on previously developed method.
PCV2 viremia or SN antibody levels could be a marker for the protection against PMWS. Therefore, these were compared with pigs in the farms during and after the outbreak of clinical PMWS. The results indicated that the farms with clinical PMWS showed high percentages of PCV2 viremia, especially PCV2b, and low SN titers.
In the study to compare the efficacy of three PCV2 vaccines using 80 piglets, overall there were differences in the vaccine efficacy among commercial PCV2 vaccines, and the differences were based on the comparison of daily weigh gain, PCV2 antibody titers, percentage of the viremic pig, and PCV2b load in sera.
Lastly, PCV2 viremia and antibody levels were compared between heavy and light weight pigs at marketing age in conventional farms with routine PCV2 vaccination. Of the 7 farms, mean IFA titer, number of viremic pig, and mean the viral loads in 3 or 4 farms were significantly different between the heavy and light weight pigs. These results suggest that PCV2 infection can be one of the causes for the light weight pigs at marketing age.
University of Minnesota Ph.D. dissertation. July 2009. Major: Veterinary Medicine. Advisor: Han Soo Joo. 1 computer file (PDF); xvi, 170 pages. Ill. (some col.)
Lyoo, Kwang Soo.
Virologic, epidemiologic, and prophylactic investigation on porcine circovirus type 2 infection in pigs..
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