PORTLAND, Ore. (KOIN) — An unusual respiratory illness has sickened dogs in several states, and veterinarians are trying to determine what’s making the animals ill while encouraging owners to take basic precautions.

Oregon, Colorado and New Hampshire are among the states that have seen cases of the illness, which has caused lasting respiratory disease and pneumonia and does not respond to antibiotics.

Symptoms of respiratory illness in dogs include coughing, sneezing, nasal or eye discharge and lethargy. Some cases of the pneumonia can progress quickly, making dogs very sick within 24 to 36 hours.

The Oregon Department of Agriculture has documented more than 200 cases of the disease since mid-August. It has encouraged pet owners to contact their vet if their dog is sick and told state veterinarians to report cases as soon as possible.

According to the department, the reported cases have fallen into three categories: chronic tracheobronchitis that lasts at least six weeks and isn’t easily treated with antibiotics; chronic pneumonia that also doesn’t respond well to antibiotics; and acute pneumonia that can severely affect canines in as little as 24 hours.

The agency is working with state researchers and the U.S. Department of Agriculture’s National Veterinary Services Laboratory to find out what is causing the illnesses.

“We’ve been undertaking a series of tests mostly looking for common sorts of expected bacterial and viral pathogens, but we’re also doing some testing for perhaps novel agents as well — novel viruses in particular,” said Kurt Williams, director of the Oregon Veterinary Diagnostic Laboratory.

Williams said dogs have died, but without a clear way to define the disease or test for it, he said it’s hard to put a number on how many died from a severe form of the infection.

As pathologists and virologists continue their research, Williams encourages dog owners to trust the process and take precautions.

“I think it’s very, very important to make sure that the animals are properly vaccinated or have a great diet, you know, all the things that we need to be doing for ourselves as far as maintaining and preventing disease: proper diet, proper exercise, proper vaccination. See your veterinarian regularly if you have concerns,” he said.

Labs across the country have been sharing their findings as they try to pinpoint the culprit.

David Needle, senior veterinary pathologist at the University of New Hampshire’s New Hampshire Veterinary Diagnostic Laboratory, has been investigating the mysterious disease for almost a year.

His lab and colleagues at the university’s Hubbard Center for Genome Research have looked at samples from dogs in Rhode Island, New Hampshire and Massachusetts and more will be coming from Oregon, Colorado and possibly other states.

He said his team has not seen a large increase in dogs dying from the illness but still encouraged pet owners to “decrease contact with other dogs.”

The Associated Press’ Devi Shastri contributed to this story.