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Multiplex test for vesicular diseases offers rapid response

Written for National Hog Farmer by Russ Daly, Travis Clement, Diego Diel (SDSU) and Rolf Rauh (Tetracore, Inc.)

 

To someone who doesn’t raise livestock, a blister popping up on a pig’s nose probably wouldn’t seem all that significant. But to pork producers, their veterinarians and regulatory officials, that blister might signal an animal health emergency.

The potential for disaster is not so much with the blister itself and its effect on the pig; it’s what it might represent for the farm and the whole pork industry. Of course, an individual pig can have a blister form due to simple trauma. When multiple pigs in a pen emerge with similar signs, though, it might indicate a more serious viral infection.

Of course, foot-and-mouth disease is at the top of the list of those blister-causing (vesicular) viral infections. While the United States has not experienced an FMD outbreak since 1929, we’ve observed the effects of that animal disease on industry, trade and national economies in other countries. The recent incursions of other foreign animal diseases such as porcine epidemic diarrhea virus have helped us understand that the threat of such disease agents entering our country is not a far-fetched possibility.

Quite appropriately, pork producers, veterinarians and animal health officials descend quickly to obtain an etiologic diagnosis when clinical signs that resemble those of vesicular FADs occur in a herd. A major obstacle to diagnosis is that blisters, or vesicles, on the snouts or feet appear similar whether caused by an FAD agent like FMD or by its close relative Senecavirus A, for example. Samples are taken and tested for the presence of FMD at the national veterinary reference laboratory. Once FMD is ruled out, however, the question of what caused the vesicles may remain.

With support from the Swine Health Information Center, South Dakota State University researchers are collaborating with Tetracore Inc. and researchers at The Pirbright Institute in the United Kingdom to develop a multiplex polymerase chain reaction test that would simultaneously detect the presence of FMD, Senecavirus A and swine vesicular disease. While FMD and SVD are foreign vesicular diseases, SVA has been recognized in the United States for several years, becoming a more-significant issue recently. This makes it more important than ever for veterinarians to have tests that can differentiate between the now-endemic SVA and the more devastating and exotic FMD and SVD. As SVA has become more established in the U.S. swine herd, the fear is that complacency could result in us missing or being late in recognizing a potential FMD outbreak.

In a PCR test, nucleic acid (DNA or RNA) is extracted from the various agents present in the sample. The addition of specific primers, and repeated cycles of heating and cooling, result in an exponential amplification of the target nucleic acid. In “real-time” PCR tests, an indicator dye fluoresces in the midst of this reaction when the nucleic acid of the target pathogen is detected in the test tube, signifying a positive test.

Most PCR tests run at SDSU and other veterinary diagnostic labs detect nucleic acid of a single pathogen, however multiplex tests are increasing in number. Multiplex PCR tests utilize the same pig sample, but can detect more than one pathogen simultaneously. Developing these tests is not as simple as throwing two “single-plex” tests together. The reagents, reaction time and temperature conditions for the test for agent A might be different than those for agent B. Tweaks and adjustments need to be made to the tests so they work together.

With the FMD-SVA-SVD multiplex test development project, SDSU researchers are working to test the SVA portion of the test, while Tetracore is coordinating the testing of FMD and SVD with other BSL-3 institutions abroad. The project currently has a “duplex” FMD-SVA PCR test in the validation phase; soon afterwards the SVD portion (courtesy of Italian researchers) will be added before final validation. Tetracore is planning to pursue a license for the multiplex assay.

SDSU researchers are involved with several other similar projects through the SHIC, including development of a universal influenza PCR test, and a test for encephalomyocarditis virus. SDSU is the lead university on the flu (Feng Li) and EMCV projects (Diego Diel), while Tetracore is leading the FMD-SVA-SVD multiplex project (Rolf Rauh).

Accurate, rapid diagnostic measures such as the multiplex PCR test may not be top of mind for most hog producers right now, but they underpin the ability of the animal health community to rapidly respond to potential health threats to the industry — whether they’re foreign or domestic.