An outbreak of a respiratory illness with an unknown cause is affecting dogs across the nation, including in Massachusetts. 

Veterinarians watching the outbreak have urged caution, but not alarm, and have recommended precautions similar to those taken for other respiratory illnesses. 

Dogs affected by the illness show symptoms similar to those of common respiratory illnesses, commonly referred to as "kennel cough." 

These symptoms include a lingering cough and inflammation of the throat, and are resistant to standard medical treatment. 

While the illness is not necessarily dangerous, some dogs afflicted with it have died after an acute bout of pneumonia. 

Guidance from the Marion Animal Hospital advises dog owners to bring their dogs to the vet if their dogs are persistently coughing, to keep their dogs away from toys, food and water bowls used by dogs from outside their household and to keep their dogs' vaccinations current. 

The Buzzards Bay Veterinary Associates issued similar guidance, adding that pet owners should keep their dogs away from large numbers of unknown dogs. 

The Massachusetts Department of Agricultural Resources said it's working with colleagues in neighboring states to better understand the illness, including the New Hampshire Veterinary Diagnostic Laboratory. It recommends kennel operators require vaccination and follow best practices for cleaning and for keeping sick animals isolated. 

Most dogs afflicted with the illness have only mild symptoms and recover within 10 days, according to the American Veterinary Medical Association. 

"Outbreaks of [respiratory illness] occur regularly, and the recent outbreak isn't cause for alarm," the Association said.