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 Peng Li, Ana Paula Poeta Silva, Daniel Moraes, Paul Yeske, Henry Osemeke, Edison Magalhaes, Gustavo Silva, and Daniel Linhares share a summary of their study comparing different PRRSV sampling methods.
Main points:
- Tonsil-oral-scrubbing (TOSc) recovered a mixture of oral fluids and tonsil exudates within seconds without restraining the sows.
- TOSc had higher PRRSV qPCR positivity and lower Ct values compared to serum and tonsil scraping in acutely infected sows.
Introduction
Few practical methods are available to monitor the PRRSV status of the sows. Serum sampling and tonsil scraping involve restraining individual sows and are labor-intensive, time-consuming, invasive, and have limited use in large-scale production settings. Thus, a practical and rapid method of sampling large numbers of sows is needed. This study developed a new sampling method, named tonsil-oral scrubbing (TOSc) and compared TOSc to serum and tonsil scraping in terms of PRRSV qPCR detection rate and Ct values in thirty matched sows post an outbreak.
Materials and Methods
A cross-sectional study was performed in a 2400 breed-to-wean herd following an outbreak. Thirty sows in the farrowing crates were conveniently selected and sampled for PRRSV qPCR testing. TOSc, tonsil scraping, and serum were consecutively collected from each sow. TOSc was collected without restraining the sows. In brief, the collected was inserted into the sow’s mouth, with the help of a headlamp, directed toward the tonsil area with an upwards angle, and scrubbed back and forth for ten seconds. The head part of the rod with sample on it was cut by a sterilized clip and then transferred to a conical tube.
Results
The TOSc samples had higher PRRSV qPCR detection rate (100%) compared to serum (16.8%) and tonsil scraping (73.3%). Moreover, TOSc samples had lower average Ct values (29.7) than tonsil scraping (30.7) and serum (35.2). (Table 1)
| Sample type | Serum | Tonsil Scraping | Tonsil Oral scraping (TOSc) |
| PCR positive rate (95%CI) | 16.8%a (7.1%, 34.3%) | 73.3%b (55.0%, 86.1%) | 100% ab (0,100%)) |
| Average Ct values and range in positive samples | 35.2 (33.6-36.4) | 30.7 (25.1-35.4) | 29.7 (24.1-36.3) |
ab: Different superscript letters indicate significant differences in least square means (Tukey test, p<0.05)
Conclusion and Discussions
Our results suggest great potential of the TOSc as a novel, practical, and rapid tool for PRRSV RNA detection in sows to be able to assess sow herd status. Some limitations of this study include the relatively small sample size and the early phase of PRRSV infection in the sampled sows, and more work needs to be done in herds that are in late closure to assess the viability of this method. This article is available at: https://doi.org/10.1016/j.prevetmed.2023.106082