Visit with a Vet: Porcine Epidemic Diarrhea Virus

Originally published in the Oct. 30, 2013, issue

 

Visit with a Georgia veterinarian in this monthly feature. This edition comes from Dr. Jeremiah Saliki, director of the Athens, Ga., Veterinary Diagnostic Lab.

 

In April and May 2013, multiple Midwestern American pig farms were simultaneously hit with a disease characterized by diarrhea and vomiting. These symptoms led clinicians and diagnosticians to suspect the coronavirus transmissible gastroenteritis virus, or TGEV, as the cause. Testing fecal samples from sick piglets using standard laboratory techniques failed to confirm these suspicions.

 

However, when the same samples were examined under an electron microscope, coronavirus particles were detected. The unexpected discovery of coronavirus particles that were negative for both US swine coronaviruses – TGEV and porcine respiratory coronavirus – prompted further testing. Tests done at Iowa State University and the Federal Laboratory at Ames were done for exotic coronaviruses, and resulted in the confirmation of porcine epidemic diarrhea virus for the first time in the US.

 

Geographic distribution, transmission and clinical signs

 

Coronaviruses are highly contagious, and the outbreaks in the US spread rapidly. Within six weeks the virus had been confirmed in about 200 hog facilities in 14 states including Arkansas, Iowa, Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, North Carolina, New York, Ohio, Oklahoma, Pennsylvania and South Dakota.

 

Sporadic outbreaks of porcine epidemic diarrhea were first identified in the United Kingdom in 1971, and this infection has become endemic in most Asian countries since 1982. There was one incursion into Canada in 1980, but it has not been reported in North America since then.

 

The virus is transmitted by the oral-fecal route, with an incubation period of three to four days. Contaminated personnel, equipment, or other fomites may introduce PEDV into a susceptible herd. The disease is difficult to distinguish from TGEV, with the main clinical sign being watery feces that may resemble tufts of wool and have an unpleasant smell. Vomiting may occur and dehydration is a secondary sign.

 

Morbidity and mortality can surpass 90 percent in suckling piglets fewer than 14 days old, but gradually decreases with age. During necropsy, histological examinations – where thin pieces of tissue are mounted on slides and viewed under a microscope – show the small intestine is inflamed with shortened villi, which indicates nutrients are not being properly absorbed, causing diarrhea.

 

Diagnosis

 

The most useful diagnostic specimen is feces or a loop of small intestine. A variety of diagnostic tests, including negative-staining electron microscopy, fluorescent antibody staining, immunohistochemical staining and virus isolation, commonly used for TGEV diagnosis are available in our laboratory for presumptive PEDV diagnosis. However, a test known as polymerase chain reaction is the only technique that can differentiate between TGEV and PEDV. The diagnostic labs in Tifton and Athens, Ga., offer a PCR technique that can detect both viruses, and  a positive result is followed by an additional test – sequencing – for definitive diagnosis.

 

PED and Georgia

 

The rapid spread of PED across the US and its occurrence in neighboring North Carolina raise concern for its possible introduction into Georgia. Fortunately, we are poised to rapidly detect the virus if it was to enter the state. The vigilance of swine practitioners and animal owners is key to detecting its incursion into our state. We recommend that PEDV testing be requested for all cases in which an acute TGEV-like disease is observed with high morbidity.

 

Some information in this column comes from the USDA Porcine Epidemic Diarrhea Technical Note and the 2012 publication “Porcine epidemic diarrhea virus: a comprehensive review of molecular epidemiology, diagnosis, and vaccines.”