A mystery dog illness that spread across the U.S. last year and can lead to serious or fatal respiratory problems is still under investigation, but cases are starting to slow, experts say.
The illness, which started to spread more widely in the summer and fall of 2023, causes coughing, sneezing and fatigue, among other symptoms, and can progress quickly to pneumonia. The dogs suspected to have it test negative for all of the typical causes of respiratory symptoms and often don't respond to treatment.
In a statement to TODAY.com, the American Veterinary Medical Association says that based on "conversations with various sources ... the number of cases are declining," adding that an "ebb and flow" of respiratory illness in dogs over the course of the year is common, similar to cold and flu season in humans.
The statement also explains that the U.S. Department of Agriculture has so far not seen that the rise in respiratory illness in dogs is linked to a new virus or bacteria.
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A statement from the Animal and Plant Inspection Service, part of the USDA, confirms to TODAY.com that the state-led testing that the agency is helping coordinate "has not indicated the presence of a novel pathogen or single infectious cause among these cases."
Numerous veterinary diagnostic labs across the country are investigating the outbreak, from Oregon to Kansas to New Hampshire.
The APHIS spokesperson adds that the illness is not regulated by APHIS and therefore the branch doesn't have data on case numbers.
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The Oregon Veterinary Medical Association also shared in an Feb. 14, 2024, update that "cases seem to be waning, if not back to normal," citing veterinarian Dr. Scott Weese's Worms and Germs blog.
At last count, at least 19 states had reported cases of the illness, according to various expert groups. The AVMA explained in an earlier statement that the mystery dog illness is difficult to track because there's no national surveillance system.
In November 2023, veterinarians in critical care settings told TODAY.com that they'd seen dozens of cases since the fall.
Late last year, multiple groups — including the Colorado and Oregon departments of agriculture, the AVMA, the Rhode Island Department of Environmental Management and the Los Angeles County Department of Public Health — issued warnings about the mystery illness in dogs.
“We don’t know what is causing this situation, where dogs are presenting at veterinarians with what private veterinarians would call kennel cough,” Rhode Island's state veterinarian Dr. Scott Marshall told NBC affiliate WJAR. “What’s different about this situation is that dogs are presenting with little bit more severe signs, not responding to usual treatments, and unfortunately had a small number, still a number, of dogs that have succumbed to them.”
“It seems to happen very, very quickly — to go from this cough that’s just won’t go away ... and then all of a sudden they develop this pneumonia,” Dr. Lindsey Ganzer, veterinarian and CEO at North Springs Veterinary Referral Center in Colorado Springs, Colorado, told TODAY.com. She said she treated over a dozen dogs with what she believes is the condition between October and November 2023.
If your dog develops a cough, do not panic, the AVMA advises. But stay vigilant about its progression and your pet's overall health, and contact your vet right away if anything seems off.
What is the mystery dog illness?
Dogs with this mystery illness usually have coughing, sneezing, eye or nose discharge, are abnormally tired, and do not test positive for any common causes of canine respiratory illness, the Oregon Department of Agriculture noted in a Nov. 9 press release.
Typically, dogs with respiratory illnesses have a cough for seven to 10 days, but some vets saw an uptick in dogs with coughs lasting weeks to months that don't respond to treatment, the Colorado Department of Agriculture said in a Nov. 22 statement.
One of the distinguishing characteristics of this mystery illness outbreak was the high number of dogs who developed pneumonia. One Colorado vet, Dr. Michael Lappin, director of the Center for Companion Animal Studies at the Colorado State University School of Veterinary Medicine, told NBC News the number of canine pneumonia cases in the state rose by 50% between September and November 2023 compared to 2022.
Marshall estimated that Rhode Island saw at least 35 cases of the mystery respiratory illness, but it's hard to know exactly how many because not all cases are reported.
Dogs are most likely to contract it by being in close contact with numerous other dogs — so places like doggy day care, dog parks, groomers or boarding kennels, Ganzer said. The illness seems to affect dogs regardless of age, size or breed, though dogs with snort snouts, like bulldogs and pugs, may be at higher risk.
Between mid-August and mid-November, the Oregon Department of Agriculture received reports of over 200 cases of the illness from veterinarians in the state but has had no additional cases to report since.
A Dec. 1 statement from the Washington Department of Agriculture said the state has received 16 reports of unusual canine respiratory disease. Two cases were confirmed as such.
The Colorado Department of Agriculture also shared in November that veterinarians in the state were seeing "double the number of cases than what is typically seen during a canine infectious respiratory disease outbreak."
The Wisconsin State Journal reported that between late October and December, clinics around the state saw six to 12 cases each, according to Dr. Keith Poulsen, director of the Wisconsin Veterinary Diagnostic Laboratory at University of Wisconin-Madison.
Dr. Amanda Cavanagh, head of urgent care services at Colorado State University James L. Voss Veterinary Teaching Hospital, in Fort Collins, Colorado, told TODAY.com that this past summer she started seeing cases of dogs with coughs lasting several weeks or longer, and the trend continued into the fall. She estimated her caseload of coughing dogs doubled from October to November.
While dogs with a contagious cough are common in veterinary settings, Cavanagh noted that she normally sees cases decrease in the fall as temperatures drop and fewer dogs are gathering at parks. "But this year, the spike has stayed high," she explains.
In its original press release, the Oregon Department of Agriculture noted that the illness can progress in three ways:
- Mild to moderate cough for six to eight weeks or longer that either doesn't respond to antibiotics or only responds a little
- Chronic pneumonia that doesn't respond to antibiotics
- Severe pneumonia that "often leads to poor outcomes in as little as 24 to 36 hours"
Cavanagh witnessed all three scenarios play out at her hospital. Last fall, she said she saw more dogs than usual with a long-lasting upper respiratory infection who then developed pneumonia from a secondary bacterial infection.
Of the dogs she treated, she said most who developed pneumonia responded to antibiotics, and many with the long-lasting cough recovered with time and never got pneumonia. But of those who developed the severe pneumonia, some died or had to be euthanized.
"That really bad pneumonia, historically, is very, very rare. Maybe I would see one case a year," but last fall alone, Cavanagh saw a "handful," she said.
How many dogs have died from the mystery illness?
Because most states are not tracking case numbers, it's not known exactly how many dogs have died from the illness.
The Oregon Department of Agriculture tells TODAY.com that it does not know how many dogs have died from the illness in the state.
However, it is confirmed that some dogs in the U.S. have died from the mystery illness.
The Colorado Department of Agriculture said in a statement that "in rare cases, the canine patients progress quickly from pneumonia to death." Colorado State University College of Veterinary Medicine and Biological Sciences also said the illness has resulted in "some fatalities."
Ganzer and Cavanagh both have had several canine patients die from what they believe to be the condition. Rhode Island Veterinary Medical Association President Shelly Pancoast told WJAR that she's seen five to 10 dogs die from the mystery illness.
“We still don’t have a great handle on how exactly we should be treating these dogs,” Pancoast said. “A vast majority of them are making full recovery, it’s just unlike anything we’ve seen in previous years with kennel cough."
What states have the mystery dog illness?
According to various expert groups, cases that match the description of the mystery dog illness have been reported, officially or anecdotally, in:
- Colorado
- California
- Florida
- Georgia
- Idaho
- Illinois
- Indiana
- Maine
- Maryland
- Massachusetts
- New Hampshire
- Nevada
- Oregon
- Pennsylvania
- Rhode Island
- Tennessee
- Vermont
- Washington
- Wisconsin
This above list of states comes from the AVMA, the Tennessee Veterinary Medical Association, the Louisiana State University School of Veterinary Medicine and the Wisconsin Veterinary Diagnostic Laboratory at University of Wisconsin-Madison.
Mystery dog illness 2023 symptoms
Symptoms of the mystery dog illness include:
- Coughing that doesn't get better on its own after a week or so
- Sneezing
- Nasal or eye discharge
- Red eyes
- Lethargy
- Trouble breathing, especially from the stomach
- Blue or purple gums (due to not getting enough oxygen)
Related: What does coughing in a dog sound like? Vet explains in viral video
Signs of coughing in dogs
For many dog owners, the signs of coughing can be difficult to recognize, Dr. Michele Forbes, Dr. Michele Forbes, owner of Compassionate Care Hospital in Ann Arbor, Michigan, says.
"Rarely do (dog owners) identify a cough until it becomes an overt problem and it’s clearly coming from the chest,” Forbes explained in a now-viral TikTok.
As a result of owners not noticing coughing or confusing it for something else, like throat-clearing or gagging, some dogs are arriving at vet facilities in more advanced stages of the condition, which can make it more difficult to treat, Forbes told TODAY.com.
Some tips to help identify signs of coughing in dogs:
- The sound dogs make when they're choking can be confused for coughing.
- Some dogs sound like they're honking, kind of like a goose.
- Coughing can also sound like the dog is gagging or clearing its throat.
- The chest may heave or the abdomen may move while the dog is coughing.
- For some dogs, it looks like they're trying to cough up a hair ball and they may produce some liquid.
- A wet cough may produce a gargling sound.
- If a dog is coughing a lot, they may end up vomiting, which dog owners often confuse for a gastrointestinal issue.
- Reverse-sneezing can be confused for coughing but it's not usually a reason to call the vet unless it's paired with actual coughing, nasal discharge or any other concerning symptoms.
When to see the vet for the mystery dog illness
Other signs that your dog should see the vet, per the AVMA, include:
- Lingering cough
- Weakness
- Loss of appetite
- Difficulty breathing
- Worsening of illness
- Cough that is sufficiently severe that it causes the dog to vomit or makes it hard for the animal to breathe
Tips to prevent mystery dog illness from vets
Dogs are most likely to contract the illness when in close contact with other dogs, so previous guidance was to keep dogs away from other dogs. But case rates have essentially returned to normal, Weese noted in his blog.
To keep your dog safe and healthy overall, the AVMA recommends keeping up to date with vaccinations. "While the existing vaccines may not specifically target this unknown infection, maintaining overall health through routine vaccinations can help support a dog’s immune system in combating various infections," it said.
The AVMA stressed the following vaccines: Bordetella, Adenovirus type 2, and parainfluenza combined with the injectable influenza H3N2 vaccine.
Be sure to give your dog two weeks after vaccination before interacting with other dogs so they can build up immunity.
If your dog is sick, consult a vet as soon as possible, as early testing can help with treatment, and keep the dog away from other dogs to avoid spreading the illness, experts advise.
While it's unlikely a humans can get sick with the respiratory illness, because the cause is still unknown, the AVMA suggests thoroughly washing hands after handling any dogs.
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Caroline Kee contributed reporting.
