Cases of the deadly Porcine Epidemic Diarrhea virus, a highly contagious pig disease, are increasing across the U.S. farm belt, a group of animal health researchers said.

Confirmed cases of PEDv increased by 252 in the week ending March 1, bringing the total number to 4,106 in 26 states, according to data released on Thursday by the U.S. Department of Agriculture’s National Animal Health Laboratory Network.

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While one case can represent an individual animal or an entire herd at a single site, swine specialists estimate PEDv has killed at least 4 million U.S. hogs since it was discovered in May 2013.

Pork processors were finding it more difficult to purchase hogs for slaughter due to the virus, which is starting to affect the pork supply and could eventually boost pork prices for consumers, industry sources said.

The Canadian Swine Health Board has confirmed that four provinces also have cases of the virus. The provinces are Manitoba, Ontario, Prince Edward Island and Quebec.

PEDv causes diarrhea, vomiting and severe dehydration in pigs. While older pigs have a chance of survival, 80 to 100 percent of piglets that contract it die.

The virus does not affect humans and is not a food safety risk.

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(Reporting by Meredith Davis in Chicago; editing by Matthew Lewis)