(Reuters) - Arizona is the latest state to confirm cases of the deadly Porcine Epidemic Diarrhea virus, a highly contagious pig disease, increasing the tally of U.S. states with confirmed cases to 27, a group of animal health researchers said.

Virginia has reported positive samples of the virus in the environment, but not yet in a hog herd, according to data released on Thursday by the U.S. Department of Agriculture's National Animal Health Laboratory Network.

Confirmed cases of PEDv increased by 274 in the week ending March 8, bringing the total number to 4,458 in 27 states.

While one case can represent an individual animal or an entire herd at a single site, hog industry analysts estimate PEDv has killed between 4 million and 5 million U.S. hogs since it was discovered in May 2013.

PEDv, which does not affect humans and is not a food safety risk, 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.

"Anytime we have a disease that cuts numbers, it cuts Checkoff income," said John Parker, spokesman for the Virginia Pork Council, referring to The Pork Checkoff which funds research, including disease research, and programs to promote the U.S. pork industry. Pork producers invest 40 cents for every $100 of hogs sold to fund the Checkoff which is governed by the National Pork Board.

"And it is the worst timing in the world because you need to promote biosecurity on farms to keep the disease from spreading," Parker added.

Senators from North Carolina and Michigan, two of the states with reported cases of PEDv, on Thursday urged the USDA to approve disaster assistance for small pork producers affected by a deadly virus that has killed more than four million pigs across the United States in the past year.

North Carolina is the second biggest hog producer in the U.S., behind top state Iowa, which is also affected by the virus.

Pork processors are finding it more difficult to purchase hogs for slaughter due to the virus which was first reported in May last year and is starting to affect the pork supply and could eventually boost pork prices for consumers, industry sources said.

(Reporting by Meredith Davis in Chicago; Editing by Marguerita Choy)