Contaminated blood from slaughterhouse pigs infected with hepatitis E could be reaching the human food supply chain, according to researchers.

“. . . 40 percent of U.S. slaughterhouse pigs (sampled) were seropositive for HEV (hepatitis E virus), indicating prior HEV infection of the pigs on the farms, which was consistent with prior estimates for farmed U.S. pigs,” according to a report just published by a team of scientists led by Harini Sooryanarain of Department of Biomedical Sciences and Pathobiology at Virginia Polytechnic Institute and State University.

The scientists went into the project knowing that in industrialized countries there are two of eight swine HEV zoonotic genotypes presenting an emerging foodborne illness threat to humans. The virus can be transmitted by consumption of raw or undercooked pork according to the research team and information from the federal Centers for Disease Control and Prevention.

It can take up to 60 days after exposure to the virus for symptoms to develop. Infected people can remain contagious for several weeks. The CDC reports that there is no vaccine for hepatitis E approved for use in the United States.

Researchers started with almost 23,000 samples from pigs from 25 slaughterhouses in 10 states. They used 5,033 samples randomly seleced and representing all 25 slaughterhouses and all 10 states. The 23,000 samples were collected in 2017-2019 for a different study and archived for future analysis. The blood samples were collected on the kill floor at the slaughterhouses, and serum was separated and stored frozen at the U.S. Department of Agriculture’s Agricultural Research Service, Beltsville Agricultural Research Center.

“We previously showed that HEV-3 is present in U.S. swine herds and that a small proportion of commercial pork products, such as liver and chitterlings, from U.S. grocery stores contain infectious HEV,” according to the scientists’ report published in the February edition of Emerging Infectious Diseases. 

“However, the current HEV infection status of U.S. market-weight pigs at the time of slaughter, the entry point to the food supply chain, remains unknown.”

Although 40 percent of the samples were seropositive, only 6 percent of the pigs had detectable HEV viremia. That is still enough for concern, according t the research team. With that many slaughterhouse pigs viremic there is concern about pork safety because blood containing infectious HEV during slaughter may contaminate raw pork products.

The scientists reported that studies have shown almost 6 percent of the U.K.’s and 44.4 percent of Scotland’s slaughterhouse market-weight pigs were viremic. A growing number of reported cases of human infection have been attributed to consumption of raw or undercooked pork.