Large numbers of pigs could be screened more quickly and cost-effectively for a range of common pathogens, such as porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza and porcine circovirus type 2 (PCV2), thanks to a new polymerase chain reaction (PCR)-based test system developed in the U.S.
The system uses samples of oral fluids which can be obtained by leaving a cotton rope in each pen for pigs to chew on. After 20 minutes or so, the rope can be retrieved and the saliva and gingival crevicular fluid squeezed into a sample bag, which then represents a pooled sample from the group. Studies have demonstrated that oral fluid samples collected in this way can form the basis of a quick and cost-effective method for screening a range of common viral pathogens.
In several experiments, samples were tested using a commercially available sample preparation and real-time PCR test system which can isolate and identify viral nucleic acid in a matter of hours. For PRRS, pooled samples of oral fluids were collected from groups of experimentally infected pigs using the rope technique, along with serum samples from each individual pig on the same days. Both serum samples and oral fluids were processed using the same Applied Biosystems preparation system and real-time PCR test, both of which were supplied by Life Technologies. The results showed that PRRSV nucleic acid was detectable in both serum and oral fluid samples from the day of infection through to 40 days after infection.
For PCV2, 24 pigs that were free of PRRSV and swine influenza were divided into four pens in separate rooms, and challenged with two different virus strains (PCV2a and PVC2b) at different times. One pen acted as a non-challenged control. Oral fluids were collected regularly up to 140 days after initial challenge and tested using real-time PCR. High titres of PCV2 were detected from day 12 to day 28 post-infection and virus was detectable throughout the entire testing period (days two to 98).
For swine influenza, a total of 180 spiked oral fluid samples were tested using real-time PCR, and subtyping reagents were also used to identify haemagglutinin and neuraminidase subtypes. The results showed that swine influenza nucleic acid was detectable in oral fluid samples spiked with high, medium and low copy numbers of swine influenza, and all positive samples could be successfully sub-typed.
"Collecting samples in this way is far less invasive for the pigs and so avoids unnecessary stress," said Christina Boss, European professional service veterinarian for Life Technologies. "And because all of the pigs will chew on the rope, it provides a very broad sample from the group, which is the key to assessing overall herd health. In addition, if the pooled sample provides a positive result, then the animals in that pen can be tested individually to identify those that are infected."
Screening for PRRS using samples of oral fluids has been gaining popularity over recent years because large numbers of pigs can be tested without increased cost or labor. The new research is due to be presented as a poster at the 4th European Symposium of Porcine Health Management in Bruges, Belgium in April.