Detecting Canine Distemper Virus

Canine distemper virus (CDV), a highly contagious and lethal disease, can cause disease outbreaks in common and endangered carnivores. There is increasing evidence that this disease is re-emerging based on cases in vaccinated dogs in Japan, Mexico, Argentina, and the United States. Because respiratory and enteric signs can mimic many other diseases, early recognition is difficult, and traditional methods of diagnosis can be time-consuming. In this study, a modified PCR methodology (reverse transcriptase insulated isothermal PCR [RT-iiPCR]) that can produce results within 1 hour was evaluated as a field test. In vitro testing for analytical sensitivity yielded a ≥95% detection rate and 95% confidence limits, indicating that its accuracy is comparable with real-time PCR (RT-PCR) for CDV detection. When RT-iiPCR and real time RT-PCR results were compared among 110 field specimens from dogs, raccoons, and foxes with suspected CDV infection, RT-iiPCR yielded 100% agreement with RT-PCR results. RT-iiPCR may prove useful as a point-of-care diagnostic test.

Commentary

Despite scrupulous vaccination protocols, distemper continues to re-emerge in outbreaks within wild canid, shelter, and companion animal populations. Because distemper resembles other respiratory and gastrointestinal diseases, rapid detection would differentiate from other diseases with similar clinical signs and help control possible outbreaks. Results from current distemper testing can take several days to a week, and other diagnostic tools (eg, cytology of inclusion bodies) are not reliable. The portable PCR tested in this study was found to be rapid (1 hour), detected low amounts of pathogen, and was roughly as sensitive and specific as current laboratory testing. It also operates without refrigeration, functions on batteries, and is rechargeable in the field. This level of versatility is essential for shelter and wildlife work but could also be used in referral hospital outbreak settings or standard laboratories. Although not discussed in this article, such a system may have future potential for other pathogens. The major practice benefits may come from future rapid turnaround from local diagnostic laboratories.—Ewan D. Wolff, DVM, PhD