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Research: New sampling guidelines for oral fluid PRRSV surveillance

21 March 2019, at 12:00am

Oral fluid sampling is becoming more popular globally as a diagnostic sampling method. Marisa Rotolo, post doc student at Iowa State University, presented a study at the American Association of Swine Veterinarians (AASV) with the objective of developing sampling guidelines for oral fluid PRRSV surveillance in commercial swine farms.

In the summer of 2014, Rotolo's team collected field data on one wean-to-finish site, with three wean-to-finish barns on site. In each barn, they collected oral fluids on a weekly basis from 36 pens in each barn. In total, 972 individual pen oral fluid samples were collected, randomized and tested for PRRS using PCR testing.

A large study was needed to ensure enough data points to estimate probability and detection. Using the field data from the individual oral fluid samples, Rotolo said they were able to model them using a piecewise exponential survival model to estimate probability of detection by sample size, disease prevalence and diagnostic assay test performance.

Study outcome

"The outcome of the study is now we have sample size estimates and probability of detection based off of prevalence in diagnostic assay performance in order to figure out how many oral fluids do you need to take on your site, in order to achieve your sampling objective," said Rotolo.

A direct comparison between oral fluids and serum samples is not available yet, so Rotolo doesn't know how many oral fluid samples equal one oral fluid sample.

"What we do know, is that oral fluids are an aggregate sample, so it's a good screening sample. It gives us a good idea of what's going on in the pen," she said. "We can take less oral fluid samples than we would serum samples, so they're a nice screening sample. You can take your oral fluid samples; you only need one person to do it, as opposed to serum collection which takes two people. Once you have your oral fluid sample, you can submit it for a diagnostic testing. Then based on those results, decide to do more targeted testing, maybe collecting serum samples or nasal swabs or whatever is going on in your site - what sample would be the best."

The study's probability of detection estimates are published in the Journal of Veterinary Microbiology. She said the results are also broadly applicable to contagious swine pathogens detectable in oral fluid samples.

Veterinarians will ultimately be able to use the tables created from the study, and based on their estimated disease prevalence, determine how many oral fluid samples should be taken in order to have confidence in their results, Rotolo concluded.