Screening for PCV2 infections via cross-sectional sampling of 146 pig herds in Belgium: an overview of qPCR results over a 3-year period

PCV2 infections can play an important role in swine respiratory disease. A feasible way of screening for PCV2 infections at herd level is cross-sectional blood sampling and qPCR analysis on pools of serum samples. The present study describes the results from VirusCheck, a service tool that includes herd information and serological investigation for PCV2.

For each herd (n=146), blood samples were collected from pigs of 3 to 5 different age groups, ranging from 6 to 25 weeks (W) (5 samples per group). Samples of each group were pooled, analyzed via qPCR and then classified as negative (≤103 PCV2 copies/ml), moderate viral load (104–106 PCV2 copies/ml) or high viral load (≥107PCV2 copies/ml). Results are grouped by age: 6-10W, 11-15W, 16-20W and > 20W of age. Herd information including clinical signs and vaccination strategy was recorded from 2015 onwards.

A total of 146 PCV2 screenings are included in the study: 62 in 2013, 35 in 2014 and 49 in 2015. The prevalence of PCV2-positive herds (at least one PCV2-positive pool) was respectively 55% (2013), 40% (2014) and 67% (2015). The clinical history of almost all participating herds mentioned growth retardation and coughing. Overall, in 2015, the proportion of negative pools per group was 82% (6-10W), 57% (11-15W), 49% (16-20W) and 64% (> 20W). A moderate viral load was detected in 15% (6-10W), 34% (11-15W), 40% (16-20W) and 36% (> 20W) of the pools, whereas a high viral load was found in limited number of pools (respectively 3%, 9%, 11% and 0%). In previous analysis (2013-2014), a high viral load was more frequently found (18%, 11W20W) and a moderate viral load less frequently (25%, 11-20W) When the data of 2015 were looked at separately for PCV2-vaccinated (12 herds) and nonvaccinated pigs (35 herds), the percentage of PCV2 positive pools were 7% (6-10W), 18% (11-15W), 20% (16-20W) and 14% (> 20W) in PCV2-vaccinated pigs versus 22%, 50%, 59% and 43% respectively in non-vaccinated pigs. High viral loads were only detected in herds without vaccination.

PCV2 infections with a high viral load (≥107 PCV2 copies/ml) became less prevalent in 2015 compared to previous years. The 2015 data also supports a protective effect of PCV2 vaccination against viremia. In line with this, the observed trend towards reduced viral loads might be explained by a higher vaccination rate in 2015 compared to 2013-2014. This hypothesis needs further investigation.

Disclosure of Interest: None Declared.