Molecular techniques in the study and control of porcine circovirus type 2

Porcine circovirus type 2 (PCV2) is an emerging virus that may result in devastating disease that affects swine herds worldwide. Only a decade has passed since researchers began to study the characteristics of the virus and the resulting diseases, and limited information was available regarding the long term presence or persistence of the virus in healthy swine herds. Our research contributes to the knowledge of the persistence of the virus in serum and semen, and the PCV2 antibody profile in healthy pigs. In addition, we developed a novel quantitative polymerase chain reaction (PCR) assay and quantified the PCV2-shedding in healthy and PCVD (porcine circovirus disease)-affected pigs. Lastly, we determined the efficacy of a novel vaccine in a subset of pigs from a PCVD-affected herd.;Porcine serum was assayed by two PCR protocols (nested polymerase chain reaction (nPCR) and non-nested PCR) and a competitive enzyme-linked immunosorbent assay (cELISA) to determine when PCV2 viremia and a rise in the serum level of PCV2-specific antibody (Ab) occurred in pigs raised in a large Canadian farrow-to-finish barn. Eight serial blood samples were collected from each of 40 pigs from 5 to 156 (±1.5) days of age; six pigs were removed from the study for various reasons at various times. Viremia was not detected in the samples collected before 72 days of age but was detected in those collected on or after 72 days: of 33 pigs, seven (21%) had only one serum sample positive for PCV2 deoxyribonucleic acid (DNA) by nPCR after day 72; 11 (33%) were intermittently positive by nPCR, non-nested PCR, or both between 72 and 156 days; and the remaining 15 (45%) were repeatedly positive (in two to four samples). The level of serum Ab against PCV2 declined after weaning and increased between 72 and 107 days of age, only after PCV2 was detected in serum. Our results show that PCV2 viremia persists in the presence of elevated levels of PCV2-specific Ab.;In a separate study, we determined the long term presence or persistence of PCV2-shedding in semen from healthy boars and the effects of PCV2 on sperm quality. A nPCR protocol was applied to porcine semen to demonstrate the PCV2-shedding patterns and duration in naturally-infected boars. Sperm morphology analysis was performed on a subset of samples to determine if the presence of PCV2 DNA in semen was associated with reduced semen quality. Semen was collected serially from 43 boars representing six breeds, aged 33.9 to 149.3 weeks. Of the 903 semen samples collected, 30 samples (3.3%) were positive for PCV2 DNA by nPCR from 13 boars. Boars shedding PCV2 DNA in semen ranged between 35.9 and 71.0 weeks of age, and shedding occurred over a period of up to 27.3 weeks. A semen nPCR test was 2.6 times more likely to be positive when collected from pigs that were ≤ 52 weeks of age and 3.0 times more likely to be positive when collected from pigs that were ≤ 26 weeks from the time of entry into the stud main unit (Generalized Estimating Equations: P=0.02; 95% confidence interval (CI) of the Odd's ratio (OR) 1.2 to 5.5 and P=0.01; 95% CI of the OR 1.3 to 6.9, respectively). PCV2 DNA was detected in semen from Duroc and Landrace boars only; however, the semen of the Hamline, Large White maternal, Large White paternal, and Meishan-synthetic boars were negative for PCV2 DNA. These results demonstrate a sporadic and long-term shedding pattern of PCV2 DNA in semen from naturally-infected boars. PCV2 DNA in semen did not have detrimental effects on sperm morphology; however, boar age and possibly breed may contribute to the persistence of PCV2-shedding in semen. (Abstract shortened by UMI.).