Tonsil scrapings for porcine reproductive and respiratory syndrome virus detection in growing pigs under field conditions

Abstract

Objective: The main objective of this study was to describe the use and limitations of tonsil scrapings (TS), oral fluids (OF), nasal swabs (NS), and environmental swabs (ES) to detect porcine reproductive and respiratory syndrome virus (PRRSV). Materials and methods: Two PRRSV-positive growing pig farms using different PRRSV control strategies were enrolled in this study. Sampling began approximately 52- and 21-days post PRRSV exposure for farms 1 and 2, respectively, and occurred once a month for four months using fixed spatial sampling. Samples for OF and ES were collected at the pen level and TS and NS samples were collected at the individual level. All samples were tested using reverse transcriptase-polymerase chain reaction (RT-PCR). Results: A total of 192 samples were collected over the study period: 48 TS, 48 OF, 48 NS, and 48 ES. Overall, 20 TS (41.6%), 0 OF (0.0%), 6 NS (12.5%), and 1 ES (2.1%) tested RT-PCR positive for PRRSV throughout this study. Implications: Tonsil scraping samples yielded more positive PRRSV RT-PCR results for longer time periods when compared to OF, NS, and ES for PRRSV detection in growing pigs. Tonsil scraping samples tested RT-PCR positive for PRRSV up to 168 days post exposure. Oral fluids, NS, and ES sampling methods for PRRSV detection in growing pig populations, particularly months after the initial infection or vaccination, should be used with caution given low RT-PCR positive samples found in this study.