Verity, a rescued black labrador puppy, was in Colorado for eight days when her new foster family realized she was sick.

Rocky Mountain Lab Rescue board member Jo Schroeder heard from Verity’s foster family on Aug. 10, just one day after they had taken in the eight-week-old puppy.

Verity looked thinner and was less active, her foster family said. Her symptoms quickly worsened — goopy eyes, fever, unwillingness to eat, a cough and rapid breathing. Schroeder and the foster family took Verity to the vet, but they couldn’t figure out what the puppy had caught and referred the group to emergency services.

Verity was hospitalized for three days as veterinary staff tried to treat her symptoms and wait for test results, but she kept getting worse.

“She was just too tiny to fight it, she didn’t even have an immune system built up yet,” Schroeder said. “She was in the hospital from the 11th to the 14th of August, and the doctor said she just couldn’t fight it anymore and we had to put her down.”

An illness with similar symptoms has been officially reported in at least four states: Colorado, Massachusetts, Oregon and Rhode Island. The first alarm bells were raised in August, when the Oregon Department of Agriculture began receiving reports of an “atypical canine infectious respiratory disease” circulating in the Portland metro and Willamette Valley areas.

Maggie Baldwin, state veterinarian with the Colorado Department of Agriculture, said it’s too early to say whether this is a new illness.

“We don’t know exactly what we are seeing, and we don’t know if it’s something new,” she said.

It’s not uncommon to see outbreaks of respiratory diseases in dogs, Baldwin said.

What’s different about this illness is how many dogs are being affected — Baldwin estimates it’s double the amount the state would normally see in an outbreak, though the department isn’t keeping an official count — and how long it lasts.

A typical respiratory illness might make a dog sick for a week or 10 days and will respond to treatment, Baldwin said. But with this illness, dogs are getting sick for weeks or months, and standard treatments aren’t helping.

Dogs develop symptoms that include coughing that doesn’t get better on its own after a week or so; sneezing; nasal and eye discharge; lethargy; tiredness; trouble breathing or rapid breathing; and blue or purple gums.

Experts aren’t sure yet if the illness is viral or bacterial, but in a Nov. 16 news release, Colorado State University veterinarians said the infection has been linked to cases of severe pneumonia and has resulted in some fatalities.

Clinical findings and tests to date suggest that this mysterious illness is a virus targeting dogs’ respiratory system, leading to a secondary bacterial infection and pneumonia, according to CSU officials.

Colorado is working with CSU and the U.S. Department of Agriculture to gather advanced diagnostic data about the illness, which will help determine whether this is a new disease or something that’s already known, Baldwin said.

Lindsey Ganzer, a veterinarian and CEO of North Springs Veterinary Referral Center in Colorado Springs, said the hospital has seen around 35 cases since the end of October.

“My main concern is with all of these cases we’ve seen, they have the commonality of having been at a doggy daycare, a boarding facility or somewhere where there’s a lot of dogs in a small area,” Ganzer said.

“However it’s spreading in those close contact areas, the holidays are coming up and a lot of owners are going to be boarding their pets, and I do think we’re going to see an increase in those cases,” she said.

For Rachael Noff, a homeowner in Parker, fear of the disease means changing schedules and locations she and her “fur baby” go to on a regular basis.

While Noff used to visit the dog park and play frisbee with her dog at least four times a week, now they use an open field behind a nearby building to get their energy out.

“The other issue is we don’t know how this mysterious disease can spread,” she said. “If dogs get it when they just happen to walk through another dog’s urine or sniff their poop? It’s pretty scary.”

Other Colorado residents commented on social media that they’ve stopped putting out communal dog water for their neighborhood pets and have canceled stays at doggy daycares or trips altogether to prevent housing their dog somewhere new.

On Saturday, the Sniff Shack — a doggy daycare, boarding, and bathing service in Denver — was one of several businesses to send out an email to its customers warning them of the potentially deadly disease.

“We are deeply concerned about this illness, yet know the upcoming Thanksgiving holiday is one of the primary weeks where you rely on us to care for your dogs as you travel to be with friends and family,” the Sniff Shack wrote in the email. “We want to keep all of our beloved Sniffers healthy and we’re going to take the following proactive steps to help minimize potential exposure to this illness.”

The Shack canceled daycare from Nov. 20 to Nov. 26 to lessen the number of dogs present to just the boarders, eliminated communal water bowls in playrooms and implemented additional cleaning and sanitizing measures.

Baldwin said people should be cautious but shouldn’t panic about the illness.

Owners should make sure their dogs are up to date on their vaccines, including for common respiratory illnesses. If a dog does become sick, owners should contact their veterinarians early to figure out the best way to move forward, Baldwin said.

Ganzer said she’s advising people to avoid communal areas for dogs, like boarding and daycare.

“If owners are going out of town for the holidays, try to find someone to come to your house to take care of your pets rather than going to a boarding facility,” she said.