SHIC-Funded Study on Senecavirus Offers Keen Insights

October 26, 2016 — 

A recent study of Senecavirus A (SVA, formerly known as Seneca Valley virus) offers valuable new insights into this increasingly important disease pathogen to the U.S. pork industry. This work, partially funded by the Swine Health Information Center (SHIC), led by Dr. Diego G. Diel, DVM, MS, PhD, South Dakota State University, has uncovered more information about the infection biology and pathogenesis of the virus that may help to ease detection, and ultimately, control of the tenacious virus.

“This study provides significant insights on the pathogenesis and infectious dynamics of SVA in swine,” Diel said. “In addition to confirming findings of previous studies that demonstrate the role of SVA as the causative agent of vesicular disease in pigs, our study shows that SVA is shed in oral and nasal secretions and feces of infected animals for up to four weeks post-infection.”

SVA Study Methodology
SVA is an emerging picornavirus that has been recently associated with vesicular disease and neonatal mortality in swine. Many aspects of SVA infection biology and pathogenesis, however, remain unknown. In this study, Diel and his colleagues investigated the pathogenesis of SVA in finishing pigs that were inoculated via the oronasal route with a contemporary SVA strain SD15-26. Then they monitored the pigs for clinical signs and lesions associated with SVA infection.

Viremia was assessed in serum and virus shedding monitored in oral and nasal secretions and feces by real-time reverse transcriptase PCR (RT-qPCR) and/or virus isolation. Additionally, viral load and tissue distribution were assessed during acute infection and following convalescence from disease.

Study Finds Tonsil Is One Primary Target Tissue
Clinical signs characterized by lethargy and lameness were first observed four days post-inoculation and they persisted for about two to 10 days. Vesicular lesions were observed on the snout and feet, affecting the coronary bands, dewclaws, interdigital space and heel/sole of SVA-infected animals. In addition, the investigators detected a short-term viremia between days 3 to 10 post-inoculation. Also, they found virus shedding between days 1 to 28 post-inoculation in oral and nasal secretions and feces.

Interestingly infectious SVA was consistently recovered from the tonsil during the first seven days of infection and, the virus RNA was detected in the tonsil of all SVA-infected animals using real-time quantitative PCR and in situ hybridization (ISH) performed on tissues collected on day 38 post-inoculation. Serological responses to SVA were characterized by early neutralizing antibody responses (5 days post-inoculation), which coincided with a progressive decrease in the levels of viremia, virus shedding and viral load in tissues.

“We have shown that SVA has a predilection for lymphoid tissues with the tonsil being one of the main targets of virus replication,” Diel said. “These results provide an improved understanding of SVA infection biology and may lead to enhanced prevention and control strategies in the future.”

What’s Next for SVA Research?
Looking ahead, Diel says there are several key questions that need to be addressed regarding SVA infection biology. They are:

1. The role of the virus on neonatal losses and diarrhea.
2. Whether the genetic differences between contemporary and historical isolates led to an increased virulence of the current isolates.
3. What is the duration of immunity?
4. Whether infected animals become carriers after convalescence from the vesicular disease.

Full article published ahead of print at the Journal of General Virology: http://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/jgv.0.000631

For more information on this and other studies funded by SHIC, click here.

The mission of the Swine Health Information Center is to protect and enhance the health of the United States swine herd through coordinated global disease monitoring, targeted research investments that minimize the impact of future disease threats, and analysis of swine health data. For more information, visit http://www.swinehealth.org or contact Dr. Sundberg at psundberg@swinehealth.org.