Davor Ojkic, Josepha DeLay
Animal Health Laboratory, University of Guelph, Guelph, ON
AHL Newsletter 2025;29(2):12.
PCR testing to determine PCV2 and PCV3 infection status is valuable for diagnostic and monitoring purposes in Ontario swine herds. Genotyping of PCV2 amplicons in PCR-positive cases can provide additional information regarding the specific virus subtype infecting a herd, subtype correlation with clinical disease, and comparison with genotypes included in available vaccines.
Annual PCV2 and PCV3 PCR results at the AHL for 2022, 2023, and 2024 are listed (Tables 1 and 2). PCV2 and PCV3, as well as PCV1, are included in the same triplex PCR assay, resulting in the same total number of annual tests for each virus. The non-pathogenic PCV1 is included in the assay for completeness.
Table 1. AHL PCV2 PCR results by case, 2022-2024.
Table 2. AHL PCV3 PCR results by case, 2022-2024.
PCV2 sequencing and genotyping is requested by clinicians for relatively few PCV2 PCR-positive cases (Table 3). Despite the small sample size, this subset does provide information regarding the PCV2 subtypes present in Ontario swine. PCV2 genotyping results over the 6 year span from 2019-2024 are provided in (Table 4). These results are also presented on an annual percentage basis (Fig.1), demonstrating the frequency of genotype identification each year. The small number of cases that are genotyped does not provide definitive information on the prevalence of PCV2 genotypes in Ontario, but the results do indicate that all recognized PCV2 genotypes except PCV2c have been detected recently in swine from this province. To determine the clinical significance of PCV2 infection, correlation with clinical findings histologic lesions, and PCV2 immunohistochemistry (IHC) or in situ hybridization (ISH) results is necessary.
Table 3. Frequency of PCV2 genotyping requests at the AHL, 2022-2024.
Table 4. AHL PCV2 genotyping results by case, 2019-2024.
Figure 1. AHL PCV2 genotyping results on an annual percentage basis, 2019-2024.
Reference
1. Segales J, Sibila M. Revisiting porcine circovirus disease diagnostic criteria in the current porcine circovirus 2 epidemiological context. Vet Sci 2022;9(3):110.