A lethal virus that causes diarrhea and vomiting in pigs has entered the United States and has been found in 14 states. With the country’s $97-billion pork industry standing to lose millions of dollars in the event of a mass outbreak, scientists are working to track the virus and prevent its spread, even as they try to understand how it passed through biosecurity defenses in the first place.
“How this virus got here, that’s the million-dollar question,” says James Collins, director of the Veterinary Diagnostic Laboratory at the University of Minnesota in St Paul.
The pathogen, a type of coronavirus called porcine epidemic diarrhea virus (PEDV), was first identified in the United Kingdom in 1971, and it caused mass epidemics in Europe in the 1970s and 1980s. As pigs there developed immunity, the virus petered out and now causes only occasional, isolated outbreaks. It has since spread to Asia, where it has been considered endemic since 1982, causing substantial economic losses to pork producers. The virus can spread quickly by a fecal–oral route and infect entire herds. And although adult pigs typically recover, PEDV can kill 80–100% of the piglets it infects. The virus poses no health threat to humans.
The US Department of Agriculture (USDA) had tried to keep PEDV and other diseases out of the country by restricting imports of pigs and pork products from certain nations, such as China. But on 10 May, the Veterinary Diagnostic Laboratory at Iowa State University in Ames confirmed that PEDV had infected pigs in Iowa, the leading producer of US pork. The lab then screened samples taken earlier from other states and found a case from Ohio submitted on 16 April that is now the earliest known US detection of PEDV, according to Gregory Stevenson, a pathologist at Iowa State. The fact that the virus has now spread to 14 states in total is a sign that the outbreak is still flaring and could become an epidemic (see ‘Pig virus on the wing’).
“It’s a real threat,” says Lisa Becton, a veterinary surgeon and director of swine health information at the National Pork Board, an industry group in Des Moines, Iowa.
To understand the virus’s enigmatic US entry, scientists are sequencing viral DNA isolated from pigs and comparing it with PEDV variants from elsewhere in the world. Researchers are also trying to create rapid diagnostic tests and vaccines to prevent the virus from spreading. The National Pork Board has approved $800,000 to fund research and education.
But PEDV must first be grown in labs — a notoriously difficult exercise because the pathogen thrives in the specific conditions found in pig guts. Researchers in Europe and Asia have already managed to infect cells, but only after years of working with the virus. In the United States, the same import restrictions that were set up to help to prevent PEDV from entering the country have made it difficult to import the necessary lab materials for working with the virus, such as vaccines, infected cells and pig antibodies.
“What’s hampering the research is that we don’t have regents,” says Linda Saif, a virologist at Ohio State University in Wooster. Access to the virus and good tests in hand “would have helped us identify which herds have been exposed, and one could have imposed more stringent control measures”, she says.