This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.
In this week’s Science Page researchers Mònica Sagrera, Laura Garza-Moreno, Marina Sibila, Salvador Oliver-Ferrando, Sonia Cárceles, Carlos Casanovas, Patricia Prieto, Alberto García-Flores, David Espigares, and Joaquim Segalés share the results of their study assessing PCV2 viremia in Spanish nursery piglets based on the farm PRRS status.
Key points:
- The detection frequency of porcine circovirus 2 (PCV-2) and porcine reproductive and respiratory syndrome virus (PRRSV) increased from 3-4 weeks of age to the end of the nursery period, and from 2020 to 2022.
- The ELISA S/P ratio tended to be lower when PCV-2 viremia was detected at more than one sampling time-point in a farm, compared to farms in which viremia was not detected or detected in only one sampling time-point.
Introduction
Porcine circovirus 2 (PCV-2) poses a significant economic threat to the swine industry. Despite PCV-2 vaccines effectiveness, co-infections, particularly with PRRSV, can exacerbate disease severity. This cross-sectional study assessed PCV-2 antibody levels in weaned piglets and measured PCV-2 and PRRSV viremia from a Spanish swine integration system in 2020 and 2022.
Materials and methods
The study design is described in Figure 1. PCV-2 antibody levels were measured at weaning by means of a commercial ELISA. Infection status evolution of PCV-2 and PRRSV was monitored by qPCR/RT-qPCR at weaning, 6 and 9 weeks. A farm was considered PCV-2 and/or PRRSV positive when at least one pool was positive in 48 farms at 2020 and in 28 of them at 2022. Farms were grouped considering their PCV-2 virological status in both years (Figure 2).
Results and discussion
The frequency of PCV-2 detection increased from 3-4 weeks of age to the end of the nursery period in both years, 2020 (2.1 to 10.4%) and 2022 (7.1 to 39.3%). Co-infections with PCV-2 and PRRSV were detected in a significant proportion of PRRSV positive farms (15% in 2020 and 60% in 2022); such increase was likely associated to the emergence of highly virulent PRRSV strains across Spain, mainly in the geographic area of sampling (Northeastern Spain).
PCV-2 ELISA S/P ratios at weaning were lower in PCV-2 qPCR positive farms at different sampling time-points compared to PCV-2 qPCR negative ones. Such result might be linked to a reduced infectious pressure over time due to continuous piglet vaccination, resulting in an overall decline in herd immunity and potentially facilitating early infections. Farms that transitioned from being PCV-2 negative in 2020 to positive in 2022 exhibited a significant increase in PRRSV detection and a decrease in PCV-2 antibody levels, which was not observed in other scenarios.
These findings highlight the need for continuous monitoring and to adapt measures to ensure effective PCV-2 vaccination practices, particularly in the context of early PCV-2 and PRRSV co-infections.
This article is available at: https://doi.org/10.1186/s40813-024-00354-0