THE BURNED OVER DISTRICT

There is a virus abroad in this country that is killing baby pigs. And other than isolating your herd, there is no way to stop it.

The porcine epidemic diarrhea virus, which is deadly only to young pigs and poses no food safety risks or danger to humans, appeared in the United States for the first time last spring in Ohio and within weeks had spread to four other states.

The outbreak led to a flurry of lab testing and a survey of the industry to determine how the virus had entered the country, comparing supplies and feeds in an effort to find a smoking gun. Farmers are cross-referencing vaccine and semen distributors, even the brands of plastic pipettes they use to inseminate sows, desperate to contain a threat that has made the industry feel increasingly vulnerable.

“It’s anybody’s guess at this point,” said Lisa Becton, director of swine health information and research at the National Pork Board, which is spending $800,000 for research into the virus.

First surfacing in Britain more than 40 years ago, the virus has spread throughout Europe and Asia. It has caused problems most recently among pork producers in China, where a 2012 strand of the disease was 99.4 percent similar to cases now found in the United States, according to researchers.

Researchers in the United States are working on a vaccine for the virus, which is passed through fecal matter and resembles transmissible gastroenteritis, another pig-to-pig illness that American farms have at times encountered. Symptoms include severe diarrhea and vomiting, and mortality rates can reach 100 percent for pigs less than a week old. Older swine will be sick for days but most likely recover.

Retroactive testing by a national laboratory pegged the earliest confirmed case of the virus in the United States around April 15 at a farm in Ohio. Within a month, other cases had surfaced in Indiana, Iowa, Colorado and Minnesota.

By the end of July, 403 separate cases had been reported to the National Animal Health Laboratory Network of the Department of Agriculture, with most outbreaks occurring in Iowa (149) and Oklahoma (94). About 30 new cases are reported each week.

“There’s not many times that a new virus hits an industry that has no immunity,” said Robert Morrison, a professor of veterinary medicine at the University of Minnesota who has been studying the virus. “Every pig in the United States is susceptible. It’s like throwing a spark on a bunch of kindling.”

So far the only hope is that older pigs who catch the disease recover and develop an immunity which they pass on to their next brood of pigs.