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.
The Science Page today is from researchers Mingyu Fan, Yang Li, Zhiqiang Hu, Lujie Bian, Weisheng Wu, Wei Liu, Lili Wu and Xiaowen Li, who take a look at oropharyngeal swab sampling for PRRSV detection in experimental and field conditions.
Key points
- In growing pigs, oropharyngeal swabs (OSs) yielded higher PRRSV-positive rates for longer periods compared to nasal swabs (NSs), Oral fluid swabs (OFs), rectal swabs (RSs), and serum samples for PRRSV detection under both experimental and field conditions.
- Collection of the oropharyngeal swab with the oropharyngeal swab tool (OST) did not require the sows housed in individual stalls to be restrained.
- OSs were more sensitive compared to serum samples in sows from 50 breeding farms sampled over a year, but the Ct-values were significantly lower in serum samples.
Introduction
Porcine reproductive and respiratory syndrome (PRRS) is recognized as a significant economic threat to the pig industry. Determining the herd-level PRRSV status is crucial for effective disease prevention and control. Established population-based sampling methods, such as oral fluids, family oral fluids, processing fluids, and tongue tip fluids, facilitate monitoring at various age stages. Although these methods increase herd sensitivity by testing more animals, they face challenges in detecting low-level PRRSV presence. The aim of this study is to evaluate the use of individual pig oropharyngeal swabs for determining PRRSV infection status in large-scale pig farms.
Materials and Methods
Six four-week-old weaned piglets were challenged with PRRSV. At each sampling time after challenge, samples of OSs, NSs, RSs, OFs, and serum were collected from each pig until 28 days post-challenge. Twenty pigs, marked with special ear tags, were randomly selected at 30 days of age on a fattening farm. Subsequently, the pigs were sampled at 30, 70, and 110 days of age. At each sampling time, samples of OSs, NSs, RSs, OFs and serum were collected from each pig. In 2022, clinical samples comprising OSs and serum from sows were collected across 50 large-scale breeding farms in China. The OSs of the sows were collected in individual stalls without any restraint (Figure 1). Each farm provided more than 30 unpaired OSs and serum samples.
Results & Discussion
In PRRSV-challenged pigs, OSs demonstrated a higher and more sustained detection rate compared to other peripheral swab samples and serum throughout the observation period. This trend was similarly observed in growing pigs over a prolonged observation period. In field conditions, the detection rate of PRRSV in serum samples of growing pigs was consistently lower than in OSs at 70 and 110 days of age. In sows, OS detection rates were more than double those of serum. Furthermore, while 17 sow farms tested negative for PRRSV in serum samples, their OSs were positive, highlighting the sensitivity of OSs. As OS sampling does not require the sow to be restrained, sampling tools and personnel are less likely to be exposed to potentially contaminated pigs and their environment. On the other hand, sampling OSs are more convenient and acceptable than serum on a large scale in sow herds. This is the first report of using OSs for the detection of PRRSV in large-scale breeding farms under field conditions. The OSs show promise as a convenient, practical, and reliable method for mass individual sampling and testing of PRRSV in large-scale pig farms, thereby enhancing the implementation of effective disease management and control measures.
The full paper is available at: https://porcinehealthmanagement.biomedcentral.com/articles/10.1186/s40813-024-00392-8