INDIANAPOLIS (WISH) — A mystery respiratory illness is causing dogs across multiple states to get sick and, in some cases, die, and experts are unsure exactly what is causing it.

The disease in some strains in parts of the country have started with a cough that eventually turned into pneumonia with other symptoms including sneezing, a fever, and a loss of appetite.

Experts at Noah’s Animal Hospital tell News 8 that, while recent reports list Indiana as one of the states experiencing the unknown illness, they have not seen a significant increase in respiratory illnesses across its nine central Indiana locations.

“Not all dogs will eat every day, but you will know if your dog is refusing food,” said Tom Dock, the director of communications at Noah’s Animal Hospital. “That’s normally an early sign that something is going on. If that is connected with a cough, with sneezing, I would recommend calling your veterinarian as soon as possible.”

Dock said the mystery illness can be fatal, but veterinarians are unsure which cases will turn out to be deadly.

“The concern right now is why are these cases going to pneumonia. And we are seeing some increased cases of pneumonia,” Dock said. “The challenge that we’re dealing with is unlike human medicine there’s not a doggy CDC so we don’t have any way to track if we’re actually seeing more increases.”

Experts were warning against boarding dogs for the holidays because close quarters with other pets could spread the illness.

“Maybe consider a pet sitter if you’re boarding over the holiday time,” Dock said. “I think right now if your dog is coughing, don’t take them to be boarded, don’t take them to be groomed.”

Flying with pets should not be a major concern.

Dock said dog owners have no need to panic but should be vigilant and proactive when it comes to any pet illnesses.

“When you hear something happening with your dog, don’t wait,” Dock said. “I tell people every day to take your pet in. If you find out everything is OK, that’s money well spent.”

Some reports say antibiotics are not working for the mystery illness, but the experts at Noah’s Animal Hospital say medicines have worked for its patients.