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Mysterious and fatal dog respiratory illness now reported in 14 states: See the map.

An unknown and potentially deadly contagious canine respiratory illness that began in one Western state this summer now spans more than a dozen states, the nation's lead non-profit veterinary organization is reporting.

As of Monday the disease had been reported in 14 states stretching from Florida to California and the cause of the mysterious illness remained under investigation, American Veterinary Medical Association (AVMA) President Dr. Rena Carlson, told USA TODAY.

In Oregon alone, veterinarians and animal sanctuary owners have reported more than 200 cases since mid-August. The remaining 13 states have not yet reported their respective numbers.

Oregon Department of Agriculture officials are working with state and national diagnostic laboratories "to identify the causative pathogen," asking veterinarians to report cases to the department as soon as possible, AVMA reported, and advising pet owners to work with a vet if their dog is ill.

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As of November 27, 2023, an unknown canine respiratory illness that began in one Western state this summer now spans at least 14 states and the cause of the mysterious illness remained under investigation, The American Veterinary Medical Association confirmed.

In another affected state, the association reported, Colorado State University College of Veterinary Medicine and Biological Sciences reported, “The possible virus, which is under intense observation by Colorado State University veterinarians, has been linked to cases of severe pneumonia and, tragically, resulted in some fatalities.”

The exact fatality number nationwide was not immediately known, AVMA spokesperson Mark Rosati told USA TODAY Monday.

Here is where the disease has been reported as well as information about symptoms, treatment and tips for dog owners as the mysterious respiratory illness lingers:

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What states have the mysterious respiratory dog disease been confirmed in?

As of Monday the illness had been reported in the following states:

  • California
  • Colorado
  • Florida
  • Georgia
  • Idaho
  • Illinois
  • Indiana
  • Maryland
  • Massachusetts
  • New Hampshire
  • Oregon
  • Rhode Island
  • Vermont
  • Washington

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Symptoms of mysterious dog disease:

According to the AVMA, common symptoms of the respiratory illness in dogs include:

  • Chronic mild-moderate tracheobronchitis − a sudden or long-term inflammation of the trachea and bronchial airways, according to Merck Veterinary Manual − lasting 6-8 weeks that is barely or non responsive to antibiotics.
  • Chronic pneumonia not responsive to antibiotics.
  • Acute pneumonia that quickly turns severe sometimes in as little as 24-36 hours.
  • Difficulty or rapid breathing, wheezing, dehydration, fever, nasal or eye discharge, weight loss, loss of appetite and lethargy.
Veterinary technician Casey Garrity, 33, right, and Dr. Amy Kalinauskas, with the Humane Animal Rescue of Pittsburgh, administer vaccines to a dog at a mobile clinic on Thursday, Oct. 26, 2023, in Pittsburgh. The American Veterinary Medical Association recommends pet owners keep their dog vaccines current as a mysterious respiratory canine illness plagues the nation.

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How is the illness spread?

Although the exact transmission of the disease remains unknown, University of New Hampshire’s Veterinary Diagnostic Laboratory senior veterinary pathologist David Needle said he believes the illness, which causes chronic respiratory problems, is likely spread through close contact and breathing in the same air as an infected animal.

Needle, who told USA TODAY he has been studying the illness for more than a year at the school's Hubbard Center for Genome Research, said the disease is not always fatal and so far, the dogs who contracted it and died had underlying issues.

Needle said he and a team from the university have been studying samples from Oregon, New Hampshire, Massachusetts and Rhode Island and are slated to begin receiving samples from Colorado and Illinois this week.

Treatments of mysterious dog illness

According to the University of Illinois School of Veterinary Medicine, outbreaks of canine infectious respiratory disease complex − also called kennel cough − often occur in shelters, boarding or training facilities over animals living in homes.

Unlike more common infections associated with kennel cough, that university reported, new cases do not respond to "standard medical therapy and can have a prolonged illness that can progress to pneumonia."

Picture, is a nebulizer, a drug delivery device used to administer medication in the form of a mist inhaled into the lungs.

Currently the treatment that dogs receive is symptomatic and supportive, Dr. Marta Vidal-Abarca, with told USA TODAY.

"This means that, since the agent causing the infection has not been identified, the treatment is not aimed at killing any pathogen in particular," Vidal-Abarca said Monday. "Instead, the treatment is aimed at mitigating clinical signs and facilitating the dog’s recovery."

Treatment, Vidal-Abarca said, includes:

  • Oxygen therapy.
  • Use of a nebulizer (a drug delivery device used to administer medication in the form of a mist inhaled into the dog's lungs).
  • Antibiotics (to treat secondary infection).
  • Measures to ensure the dog has "adequate nutrition" and hydration (including the use of intravenous fluids).

Tips for dog owners to avoid the mystery respiratory illness

Although researchers are not yet sure what causes the illness, below are tips from the AVMA and Vidal-Abarca as well as other vets, to help avoid your dog from becoming infected with it.

  • Make sure your dog has been fully vaccinated - especially for kennel cough. While the existing vaccines may not specifically target the unknown infection, maintaining overall health through routine vaccinations helps support a dog’s immune system.
  • Avoid dog parks, pet stores and grooming facilities with your canine companion, if possible.
Dog run around the newly opened Muth Family Dog Park, Saturday, June 24, 2023, in Sheboygan, Wisconsin. The American Veterinary Medical Association recommends pet owners keep their dogs out of commonly shared areas including dog parks and grooming facilities as a mystery canine respiratory illness plagues the nation.
  • Be mindful of boarding. It is recommended to avoid boarding your dog "unless absolutely necessary. Caution is advised rather than worry. There is a lot of interstate mobility among people and their pets and this may facilitate the transmission of the disease, as it appears to be highly contagious."  
  • If your dog shows any signs of respiratory issues, including the symptoms listed above, contact your vet and keep your pet isolated from other animals until the matter is resolved.

Until the cause is determined, Michael Stepien, a spokesperson with the United States Department of Agriculture, said the federal agency will "continue supporting states with testing when needed," but noted the agency's support role is limited to testing and collaborating with partners.

Contributing: Saman Shafiq

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at and follow her on X @nataliealund.

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