SHIC adds PCR tests to assay catalog

SHIC adds assays for sapovirus and pseudorabies to diagnostic catalog.

September 25, 2020

3 Min Read
SHIC adds PCR tests to assay catalog

Two new polymerase chain reaction (PCR) tests have been added to the Swine Health Information Center (SHIC) Diagnostic Assay Catalog.

SHIC said a highly sensitive and specific real-time PCR (RT-PCR) for detecting porcine sapovirus (SaV) genotype III for neonatal diarrhea investigation, as well as a single-tube triplex RT-PCR assay for differential detection of variant strains of pseudorabies virus (PRV), including the Chinese highly pathogenic strain, gives diagnosticians previously unavailable valuable tools.

Those are now available to all veterinary diagnostic laboratories for use and fit with SHIC's mission to make sure the U.S. swine industry is prepared for emerging diseases, the center said.

The sapovirus PCR project resulted from a farm's refractory case of piglet diarrhea in the lactation phase for more than two years. Pigs in the case study exhibited self-limiting diarrhea starting around 10 days of age but typically lost 1-2 lb. of expected weaning weight, SHIC said. Researchers use of four independent lines of evidence in this case — metagenomics analysis, RT-PCR, histopathology and in situ hybridization — confirmed porcine SaV of genogroup III as the cause of the enteritis and diarrhea.

A subsequent prevalence survey of more than 500 samples comparing pigs with clinical diarrhea and clinically healthy pigs suggests that porcine SaV genotype III may play an important role in causing swine enteritis and diarrhea, SHIC reported.

SHIC also noted that the study findings provide significant insights for a better understanding of the epidemiology and pathogenicity of porcine SaV. To the researchers' knowledge, this is the first evidence that SaV likely serves as the sole etiological agent causing enteritis and diarrhea of piglets in the field in the U.S. Having effective diagnostics for pathogens on the Swine Viral Disease Matrix and the Swine Bacterial Disease Matrix is key to discovery and detection, which are essential for effective management, SHIC said.

The single-tube triplex RT-PCR assay for differential detection of variant strains of PRV is able to differentiate wild-type classical (Bristol) and Chinese variant PRV and the gE-deletion PRV mutant marker vaccines, SHIC explained. It could be used as a rapid diagnostic tool for foreign animal disease detection in North America or for surveillance and in epidemiological studies in countries like China, where both classical and variant strains of PRV are endemic.

The clinical specificity and sensitivity of the assay was evaluated using whole blood, serum, tissue and swab samples collected from known negative and experimentally inoculated pigs with either classical (Bristol) or variant (JS-2012 and HeN1) PRV strains, SHIC reported. The targeted genomic region of this assay is also deleted in commonly used PRV gE-deleted marker vaccines, and therefore, the triplex assay did not detect viral DNA extracted from two commercial vaccine strains Bartha K-61 and Bucharest.

SHIC said this single-tube triplex assay can be used for routine diagnostics and epidemiological studies for detection and differentiation of classical strains from variant strains of PRV and as a differentiation of infected and vaccinated animals (DIVA) assay when PRV gE-deletion mutant marker vaccines are used.

As the world deals with the COVID-19 pandemic, SHIC said it continues to focus efforts on prevention, preparedness and response to novel and emerging swine disease for the benefit of U.S. swine health. As a conduit of information and research, SHIC encourages the sharing of its publications and research, which may be forwarded, reprinted and quoted freely. SHIC is funded by America's pork producers to fulfill the mission to protect and enhance the health of the U.S. swine herd.

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