SHIC Funded Diagnostic Research Finds Saliva and Nasal Swabs vs. Serum are Good for Testing for PPIV1

February 7, 2018 — Paul Sundberg

Porcine Parainfluenza Virus 1 (PPIV1) is widespread in US swine herds. Now better diagnostic capability is available to help understand its potential role in disease. Swine Health Information Center (SHIC) funded research has successfully developed and validated a TaqMan quantitative RT-PCR (qRT-PCR) test for PPIV1 detection in oral fluid saliva and nasal swabs. No PPIV1 RNA was found in serum samples even from pigs that showed a high level of viral RNA in their nasal swabs. This is one of many new diagnostic tests developed over the past few years under SHIC's research umbrella to increase US readiness for emerging diseases.

SHIC asked Dr. Yanhua Li from Kansas State University to develop and validate a PPIV1 PCR that diagnostic labs could adopt. Dr. Li works in the Molecular Research and Development Laboratory at Kansas State Veterinary Diagnostic Laboratory. This laboratory has developed over 50 molecular diagnostic assays or DNA sequencing procedures to validate and improve molecular diagnostic methods for pathogens. This team also specializes in exploring new technologies to increase throughput capabilities in labs.

Using available viral sequences in GenBank, Dr. Li designed a one-step real time qRT PCR assay targeting the HN gene of PPIV1. The assay developed showed very high diagnostic sensitivity and specificity for detecting PPIV1 in nasal swab and oral fluid samples. Offering complete coverage to current PPIV1 strains, the rapid and sensitive diagnostic tool developed will be useful for diagnostic of PPIV1 infection which will aid in epidemiological surveillance.

Of note to veterinary practitioners is that no PPIV1 RNA was detected in serum samples even from pigs that showed a high level of viral RNA in their nasal swabs. Due to lack of viremia in pigs, serum is not a good way to test for PPIV1.

With this new diagnostic ability in saliva and nasal swabs, comes encouragement from SHIC to figure out if early respiratory cases and other clinical signs may be tied to PPIV1, so we can better understand impact and prevalence of this virus in US herds.

When the SHIC Swine Disease Matrix was researched and developed to prioritize emerging and foreign diseases of focus, PPIV1, a paramyxovirus, made the list and gaps in knowledge were assessed. These gaps included the virus' host range, transmission modes, and pathogenesis. As some viruses in the paramyxovirus family (like Nipah Virus) cause serious disease in humans; it was determined the potential for zoonotic transmission needed to be examined further. Alongside this, experimental infections in pigs had not been conducted. And important to all the above, we didn't have a good test to detect the virus. Developing this became step one.

First found in 2013 in Hong Kong, clinical signs associated with PPIV1 in pigs include lethargy, coughing, sneezing, and serous nasal discharge. Young pigs (under 21 days) seem most likely to develop clinical disease. However, the virus has also been detected in asymptomatic pigs. There are no pathognomonic lesions caused by PPIV1, and the likelihood of viral co-infection makes the interpretation of observed signs and lesions difficult. Thought to be transmitted via the respiratory route for a viral shedding period of 2-10 days, it is unclear whether other modes of transmission occur. The PPIV1 Fact Sheet on SHIC's website recommends that it should be considered as a differential when commercial pigs are showing symptoms of respiratory illness, but test negative for known respiratory pathogens.

For incidents of high or ongoing morbidity or mortality where an etiology is either not identified or there is a strong suspicion that the identified etiology is not the likely cause of the outbreak, SHIC offers support for the need for further diagnostic workup to identify newly introduced or emerging swine diseases. Read more about diagnostic fee assistance here.

Funded by America's pork producers to protect and enhance the health of the US swine herd, the Swine Health Information Center focuses its efforts on prevention, preparedness, and response. As a conduit of information and research, SHIC encourages sharing of its publications and research for the benefit of swine health. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Paul Sundberg at psundberg@swinehealth.org.

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Paul Sundberg, Executive Director, Swine Health Information Center