Development of a Quantitative, Competitive-PCR (QC-PCR) Assay to Determine the DNA Load of Porcine Circovirus Type 2 (PCV2) in Blood and Fecal Swabs

Abstract

PCV2 is an essential causative agent of post-weaning multisystemic wasting syndrome (PMWS). The detection of PCV2 is not the defi nitive diagnosis since PCV2 infection does not always lead to PMWS; however, viral load may relate to PCV2-induced PMWS. In this study, a quantitative, competitive-polymerase chain reaction (QC-PCR) assay was developed to determine the amount of PCV DNA in whole blood and fecal swabs of pigs from PMWS-affected and PMWS-nonaffected farms. The QC-PCR was based on competitive co-amplifi cation of a 345 bp fragment of the PCV 2 in the samples with a known concentration of the competitor DNA, which produced a 513 bp fragment. Blood and fecal swabs were collected from 140 pigs from 11 PMWS-affected and 14 PMWS-nonaffected farms. The results demonstrated that the PCV2 DNA from fecal swabs of pigs in the PMWS-affected farms ranged from less than 1 fg.μL^-1 to 100 pg.μL^-1 with a mean PCV2 DNA concentration of 6.42 × 10⁷ copies.mL^-1, which was signifi cantly higher than that from PMWS-nonaffected farms (3.8 × 10⁵ copies. mL^-1). The results indicate correlation of PCV2 viremia and shedding to the development of PMWS. Therefore, the QC-PCR technique developed here could be applied as a tool to predict trends of the emergence and spread of the disease.