How Many Oral Fluid Samples for PRRS are Needed?

Oral-fluid sampling can provide a simple, reliable way to surveil for porcine reproductive and respiratory syndrome virus (PRRSV), Marisa Rotolo, DVM, of Iowa State University, reported at the 2017 American Association of Swine Veterinarians conference.

Rotolo and colleagues came to this conclusion based on a research project they conducted using a statistical tool known as spatial autocorrelation. Spatial autocorrelation, in simplest terms, means everything is related to everything else, but near things are more related than distant things, Rotolo explained in an interview with Pig Health Today after her presentation.

For the pork industry, this would mean that pigs in pens near each other are more likely to have the same disease status than pens that are farther apart, she said.

The investigators also determined if it’s better to collect samples for PRRSV testing that are equal distances from each other — a process known as fixed-spatial sampling — versus collecting samples from random locations throughout a barn, she said.

For their research project, Rotolo and colleagues collected oral-fluid samples in three wean-to-finish barns weekly from 108 pens with about 25 pigs per pen. In all, they had 972 samples, which were completely randomized, then tested for PRRSV with reverse transcription polymerase chain reaction. They used statistical analyses to compare the probability of detection based on random versus fixed-spatial sampling.

They found that PRRSV did indeed exhibit spatial autocorrelation and that oral sampling using fixed sampling was an effective strategy that can provide a good representation of what’s going on in a barn.

Oral-fluid sampling, she added, is a particularly attractive sampling method because it’s easy to perform and takes only one person. In contrast, collecting serum samples requires two people — one to restrain the animal and another to collect the sample — which also increases labor costs, Rotolo said.

Editor’s Note: Portions of this article appeared previously in Pig Health Today.




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