Veterinary laboratories in several states are investigating an unusual respiratory illness in dogs, and encouraging people to take basic precautions to keep their pets healthy as veterinarians try to pin down what's making the animals sick.

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 pneunomia 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. 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.

Dogs have died, said Kurt Williams, director of the Oregon Veterinary Diagnostic Laboratory at Oregon State University. 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.

Williams had a simple message for dog owners: “Don’t panic.” He also said dog owners should make sure that their pets are up to date on vaccines, including those that protect against various respiratory illnesses.

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.”