Vesicular disease may be rising in swine

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Cases of vesicular swine disease appeared to be increasing this summer, according to an organization that monitors swine health.

The vesicular disease caused by the Seneca Valley virus, also known as Senecavirus A, produces clinical signs similar to those seen with foot-and-mouth disease. Slaughter plants that find unexplained lesions on pigs have to treat those pigs as potential carriers for FMD, shutting down a plant for investigation, according to information from the Swine Health Information Center.

The July 27 report of increased illnesses came from the Swine Health Monitoring Project, a Swine Health Information Center–funded collaboration among universities.

A chart published with the report indicates veterinary diagnostic laboratories at Iowa State University, the University of Minnesota, and South Dakota State University confirmed about 190 Senecavirus A infections from August 2015 through July 2016, a mean of about four a week. Most of those infections were reported in fall 2015 and the first three months of 2016, with reports dropping off in December 2015 and bottoming out April through June 2016.

Bar chart: Laboratory-confirmed infections with Seneca Valley virus, August 2015 – July 2016
Source: the Swine Health Information Center (click to enlarge)

The laboratories then confirmed 14 infections in the three weeks ending July 20.

Dr. Paul Sundberg, executive director of the SHIC, noted that the data mix reports of new infections and tests on existing infections without distinguishing between them. He also said in early August that infection reports had increased during the same period of 2015 and peaked in early fall.

Dr. Sundberg also noted that the Department of Agriculture has reported seeing increased investigation of vesicular disease at slaughter plants.

The information center is suggesting that, when lesions are found in pigs, veterinarians investigate under the direction of state or federal animal health officials, who can determine whether a foreign animal disease investigation is needed, Dr. Sundberg said. The monitoring program report states that lesions should be allowed to heal before pigs are shipped to slaughter facilities. When holding the pigs is impossible, communication is needed between the packing plant and animal health officials to avoid disruptions.

The swine industry also is investigating a novel virus that could cause neurologic disease.

A separate report from the SHIC indicates a novel porcine sapelovirus is implicated in an acute outbreak in the U.S. of atypical neurologic disease associated with polioencephalomyelitis. The outbreak occurred among 11-week-old pigs in an approximately 3,000-pig herd in a central East Coast state, according to information from the SHIC and Dr. Paulo Arruda, who works at the Iowa State University Veterinary Diagnostic Laboratory and was the primary diagnostician and one of the authors of the report.

The outbreak had a 20 percent morbidity rate and a 30 percent case fatality rate.

The cause of the disease remained unconfirmed at press time. But histopathologic lesions observed in pigs with disease suggested the presence of a neurotropic virus, and the novel sapelovirus was the only viral agent identified in CNS tissues of affected animals, according to the report and Dr. Arruda.

“The biologic relevance of this finding is not clear at this point as there is a significant gap of knowledge concerning the pathophysiology and the potential role of this particular virus in cases of encephalomyelitis in swine,” the report states. “Historically, similar cases have been sporadically associated with ‘enterovirus infection’; however, serotyping was not commonly performed and therefore true prevalence of cases associated with specific enterovirus serotypes are not known to this date.”

Dr. Sundberg noted that, as in this case, the center funds investigations into outbreaks with unexplained etiology if initial diagnostic results fail to provide satisfactory answers. More is available here.

Related JAVMA content:

Vesicular disease found in more swine herds (Oct. 15, 2015)