A mystery illness sickening dogs across the U.S. is continuing to spread and concern veterinarians. At least 19 states have seen cases, according to expert groups.

The American Veterinary Medical Association explained in a statement on the mysterious canine respiratory infection that it’s difficult to track because there is no national data tracking for canine illnesses. Anecdotally, veterinarians in critical care settings tell TODAY.com that they’ve seen dozens of cases since the fall.

The illness itself usually starts out as a cough, which can last for weeks to months and does not respond to typical treatment, such as antibiotics or antivirals. In some dogs, the cough progresses to pneumonia, and in some cases, the pneumonia can turn fatal if the dog ends up struggling to get enough oxygen.

Since early November, multiple groups, including the Colorado and Oregon departments of agriculture, the AVMA and the Rhode Island Department of Environmental Management, have 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 or canine infectious respiratory disease,” 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.”

Dr. Lindsey Ganzer, veterinarian and CEO at North Springs Veterinary Referral Center in Colorado Springs, Colorado, tells TODAY.com that since October she’s seen upwards of 30 dogs with what she believes is the condition. Many of the dogs coming require hospitalization, and several have died.

“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,” she says.

Ganzer notes that the illness seems to be affecting dogs regardless of age, size or breed, but it’s most common in dogs who recently spent time with other dogs, such as at a kennel or doggy day care.

That’s why many veterinarians and expert groups are urging dog owners to keep their canines out of boarding facilities, groomers and anywhere else dogs tend to gather in groups for the time being.

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 have seen 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 is the high number of dogs who are developing 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.

According to pet insurance company Trupanion, claims for dogs with respiratory illness are on the rise in several states.

Marshall estimated that Rhode Island has seen 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 day care, dog parks, groomers or boarding kennels, Ganzer explains.

Between mid-August and mid-November, the Oregon Department of Agriculture has received reports of over 200 cases of the illness from veterinarians in the state, and they’re still coming in.

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 and are recovering. The department is still collecting data on the other 14. “This is the time of year that dogs tend to get respiratory illnesses, but veterinarians report that the majority of cases are recovering. A small portion of animals do experience serious disease,” the statement noted.

The Colorado Department of Agriculture also shared that “veterinarians (in the state) are currently reporting that they are seeing double the number of cases than what is typically seen during a canine infectious respiratory disease outbreak.”

The Wisconsin State Journal reported that since late October, clinics around the state have seen between 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, tells TODAY.com this past summer she started seeing cases of dogs with coughs lasting several weeks or longer, and the trend has continued into the fall. She estimates her caseload of coughing dogs has doubled over the past month or so.

While dogs with a contagious cough are common in veterinary settings, Cavanagh notes 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 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 has witnessed all three scenarios play out at her hospital. Recently, she’s seen more dogs than usual with a long-lasting upper respiratory infection who then develop pneumonia from a secondary bacterial infection. In a small subset of these dogs, the pneumonia can be “really severe,” she explains.

Of the dogs she’s treated, she says most who develop pneumonia respond to antibiotics, and many with a long-lasting cough recover with time and never get pneumonia. But of those who develop the severe pneumonia, some have died or had to be euthanized.

“That really bad pneumonia, historically, is very, very rare. Maybe I would see one case a year,” Cavanagh says. “We’ve seen a handful of them in the past weeks to months.”

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.”

Why is respiratory illness in dogs rising?

While this mystery dog illness is making headlines in 2023, Ganzer notes that it’s been around since last year. Her hospital has been sending off samples from the dogs to University of New Hampshire’s Veterinary Diagnosis Laboratory, which has been studying the illness since 2022.

One of the biggest challenges of this mystery illness is defining what cases “fall under this umbrella of this particular entity that we’re all investigating,” explains Dr. Kurt Williams, director of the Oregon Veterinary Diagnostic Laboratory, which has been investigating the illness since the fall. That’s because dogs can develop a cough for many reasons, and it takes time to rule out known causes.

“We’re still trying to pin down a potential cause or causes for the entity. At least in Oregon, it’s given us some some challenges,” Williams tells TODAY.com.

Researchers at University of New Hampshire’s Veterinary Diagnosis Laboratory told NBC News that they’ve identified a bacterium that could be behind the surge in respiratory illness in dogs, but more testing is needed to confirm.

It’s also possible that the cause is a bacteria or virus that has been around for a while but hasn’t been identified before, according to Dr. Scott Weese, a pathobiology professor at the University of Guelph Ontario Veterinary College and director of the university’s Centre for Public Health and Zoonoses.

“The current disease patterns don’t really fit with emergence of a new highly transmissible pathogen,” he said, according to an AVMA statement. ““Of course, we’re always worried about a new bug, (but) most times the strange cases we see are just the usual suspects behaving a little bit differently.”

Another possible reason for the rise in severe respiratory illness in dogs in 2023 is that they may be getting infected with multiple viruses or bacteria at a time, Dr. Deborah Silverstein, section chief of emergency medicine and critical care at the Ryan Veterinary Hospital at the University of Pennsylvania, told NBC News.

Some dogs may also have lowered immunity due to pandemic-era restrictions on boarding and day care, and vaccination rates in dogs are also dropping, experts say.

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.

In recent weeks, there have also been multiple reports of outbreaks of a deadly respiratory illness in dogs at animal shelters in the U.S. The San Diego Humane Society has lost four dogs to a “severe respiratory canine illness,” according to a Nov. 15 press release.

However, the outbreak at San Diego Humane Society has been linked to two particular bacteria, Strep zoo and Mycoplasma. Dr. Zarah Hedge, chief medical officer at San Diego Humane Society, tells TODAY.com that she believes the outbreak at her shelter and others she’s heard about — such as one in Las Vegas — are not related to the mystery dog illness. That’s because Strep zoo and Mycoplasma are easily treatable with the right antibiotics, which saved many dogs at her shelter during the recent outbreak. Also, the sick dogs she saw didn’t have a long-term cough, she says.

The AVMA also confirmed there’s no indication of a connection between the outbreaks.

That said, Hedge is still concerned about the damage that severe respiratory infections, both known and unknown, can cause in dogs, especially in shelters.

“We are seeing numbers of dogs coming into shelters that we haven’t seen in a very long time,” Hedge says. “A lot of shelters across the country are overcrowded, and it just sets you up for disease outbreaks.”

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

“Owners should monitor their dogs closely for progressive coughing that may be accompanied by signs of ocular or nasal discharges and sneezing,” the AVMA said in a statement.

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 tells 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

Ganzer says her No. 1 tip is to keep dogs from areas where they’re likely to come into contact with other dogs (but do not delay taking your dog to the vet for needed medical care). Cavanagh advises dog owners across the country, regardless of whether they live in a state where cases have been reported, to follow this guidance.

Keeping dogs out of these situations may be difficult for many families during the holidays because many people rely on boarding kennels when they travel. However, Ganzer says to avoid boarding dogs over the holidays “if at all possible.”

“I understand that there are circumstances that are unavoidable and that some people have to (board their dogs), but I would not take this lightly,” she explains. “If there’s somebody that can even just come to your house and let your dog out, that’s a better option.”

In light of the situation, Cavanagh says she’s been keeping her two dogs at home and avoiding settings where they may come in contact with other dogs. She also suggests avoiding any nose-to-nose street greetings between strange dogs.

“In the same way that people spread germs and illnesses by interacting with other people, dogs transmit disease when congregating with other dogs,” Marshall said. “For this reason, and particularly until the agent causing the illness is known, we are recommending that dog owners avoid needless risks of exposure.”

Williams agrees that it’s “prudent” to be concerned right now about putting dogs in scenarios where they may come into contact with many other dogs. If you need to put your dog in such a situation, he suggests contacting your vet ahead of time for guidance.

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. It stresses 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 right away, as early testing can help with treatment, and keep the dog away from other dogs to avoid spreading the illness, the Colorado Department of Agriculture advises.

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.

If your dog has been diagnosed with the mystery coughing illness, Ganzer suggests asking your veterinarian about submitting a sample to a research lab to help with the efforts to identify the cause.

Caroline Kee contributed reporting.