Origin of U.S. PEDV strains tracked

Veterinary researchers have identified the potential evolution of the PEDV strains discovered in the U.S. earlier this year.

Veterinary researchers at the Virginia-Maryland Regional College of Veterinary Medicine at Virginia Tech announced Oct. 22 that the origin and possible evolution of porcine epidemic diarrhea virus (PEDV), an emerging swine virus with high mortality rates that has spread to at least 17 states, has been identified.

A team of researchers led by Dr. X.J. Meng, university distinguished professor of molecular virology, used virus strains isolated from the ongoing outbreaks in Minnesota and Iowa to trace the likely origin of PEDV to a strain from the Anhui province in China. PEDV was first recognized in the U.S. in May.

“The virus typically only affects nursery pigs and has many similarities with transmissible gastroenteritis virus of swine,” said Meng, who is a faculty member in the department of biomedical sciences and pathobiology. “There is currently no vaccine against (PEDV). Although some vaccines are in use in Asia, we do not know whether they would work against the U.S. strains of the virus.”

The researchers determined not only that the three U.S. strains of PEDV are most closely related to the Chinese strains of the virus, but also that the U.S. strains likely diverged two or three years ago following an outbreak of a particularly virulent strain in China. They published their findings on the “Origin, Evolution, and Genotyping of Emergent Porcine Epidemic Diarrhea Virus Strains in the United States” in the Oct. 15 issue of the American Academy of Microbiology journal mBio.

According to the study, the U.S. strains of the virus share 99.5% of their genetic code with their Chinese counterpart. Allan Dickerman, a co-author of the paper and research assistant professor at the Virginia Bioinformatics Institute, performed the molecular clock analysis to determine that the divergence of the U.S. and Chinese virus strains coincides with a PEDV outbreak in China back in December 2010. Meng said it is unclear whether the U.S. strains of the virus diverged in China or in the U.S.

The sudden emergence of PEDV, which belongs to the coronavirus family, has caused economic and public health concerns in the U.S.

Researchers have found no evidence that the virus can spread to humans or pose a threat to food safety. They did, however, come across additional evidence that the U.S. strains share several genetic features with a bat coronavirus — findings which point to an evolutionary origin from bats and the potential for cross-species transmission.

Though commonly accepted that the virus spreads through the fecal-oral route, Meng said scientists have not yet ruled out the possibility of other transmission routes. Symptoms include acute vomiting, anorexia and watery diarrhea with high mortality rates in pigs less than 10 days old.

“Veterinarians need to recognize the symptoms of the disease, and with the lack of a vaccine in the U.S., practicing strict biosecurity and good sanitation procedures on the farm are important for prevention and control of this deadly disease,” Meng added.

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