Processing fluids helping to fine tune diagnostics in swine herds thought to be PRRS-negative

Collecting aggregate samples of processing fluids during tail docking and castration is proving to be an excellent way to monitor herds for porcine reproductive and respiratory disease (PRRS) virus, Will Lopez, DVM, Iowa State University, told Pig Health Today.
calendar icon 19 July 2018
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Lopez said this method is yielding “amazing” results and can detect the presence of PRRS virus early and save producers time and money.

The procedure simply involves placing all tails and testicles removed during processing into a bucket lined with a plastic bag and cheesecloth, which are secured around the top of the bucket with a large rubber band. Fluids from the tissues drain through the cheesecloth into the plastic bag. After collection, a small hole is made into the bottom of the plastic bag so fluids can be funnelled into testing vials and sent to a lab for testing.

Better sensitivity

Results of a study conducted by Lopez and colleagues showed processing-fluid testing detected PRRSV RNA by rRT-PCR (real-time reverse transcription-polymerase chain reaction) with far greater sensitivity compared to results with matched individual pig blood sera or tail blood swabs pooled into groups of five.

The procedure is better than oral-fluid sampling using ropes in some situations, Lopez noted, because it can be difficult to get very young pigs to chew on ropes.

So far, the highest sensitivity with the processing-fluid method has been found when fluids from an entire day of collection are tested by PCR, he said.

It’s not uncommon, Lopez explained, for re-breaks of PRRS to occur on farms thought to be negative or stable for PRRS with the same strain of virus detected before a control or elimination plan was implemented. This suggests the virus was never gone and that it can circulate at a very low prevalence for an undetermined period of time.

Test more pigs, more often

“That’s kind of the motivation we want. We need to test more pigs more frequently in order to really increase our probability of detection of the virus at near-zero prevalence,” he said. With processing fluids, the sample size can be increased as well as the frequency of testing. Less labour time is required for testing. It also costs less.

There are limitations, however. This method does not reveal how many piglets are positive out of the sample, but Lopez and colleagues are working with statistical processes that might help determine how many piglets are positive or negative in a given sample. The other downside is the possibility of environmental contamination of samples.

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