A mysterious respiratory illness that infects dogs is spreading across the US. Here's how to protect your pooch, and what to do if you think they have it.

• Dogs across the country have been falling ill with an unidentified sickness.
• Its symptoms include coughing, sneezing, runny nose, and energy loss.
• If symptoms persist, the disease can develop into pneumonia, which has been fatal in a few cases.

A mysterious respiratory illness is spreading between dogs across the US, and veterinarians aren't sure what's causing it. In some cases, it's been deadly.

It's not uncommon for dogs to develop a cough this time of year, Dr. Sorin McKnight, an associate veterinarian at Wellborn Road Veterinary Medical Center in Texas, told Business Insider.

But what's concerning about this disease, which McKnight herself hasn't witnessed, is that vets don't yet know if it's caused by a familiar bug, like the flu, or something new entirely.

If they don't know what it is they don't know how to treat it, McKnight said, "so the unknown part I think like, is the unsettling part."

A group of scientists at the University of New Hampshire's Veterinary Diagnosis Laboratory and the Hubbard Center for Genome Studies thinks they may have identified a bacteria that could be responsible, but it hasn't been confirmed yet, NBC news reported.

But these reports could be caused by different bugs, and it's important not to panic, veterinarian Dr. Silene St. Bernard, who is the regional medical director working with VCA animal hospitals, told BI.

Some of the first known reports of the disease started in Oregon in early August. Since then, the state has recorded more than 200 case reports of the disease, Andrea Cantu-Schomus, communications director of the Oregon Department of Agriculture, told the American Veterinary Medical Association.

Other states that have reported cases include Colorado, New Hampshire, and Massachusetts.

Here's what to look out for in your pooch, and how to do your best to protect your dog against infection.

How to protect your pup

The first line of defense in dogs is the same as humans — staying up to date with vaccinations, McKnight said. The shots are helpful in keeping your dog protected against other sicknesses that might make their immune systems weaker, St. Bernard said.

But the easiest way to avoid it is just to keep your dog away from others. Like kids at school, infection spreads easily in areas of high traffic, like dog parks, boarders, and groomers, McKnight said.

It probably spreads through direct contact with an infected dog or by coming into contact with fluids from an infected dog, St.Bernard said.

"I think we've all learned more than we ever wanted to know about respiratory disease and how it passes over the last few years. But it wouldn't be any different really in dogs than it would people," she said.

So with transmission in mind, keeping your dog away from others for a little while, "would be the best way to avoid it. You know, just trying to stay away to not get infected," McKnight said.

It's especially prudent to take note of this ahead of the holidays when many people opt to board their dogs as they travel.

What to do if you think your dog got infected

Symptoms differ from case to case but tend to mirror that which you might see in humans: cough, sneezing, runny nose, and low energy, the Associated Press reported.

Sometimes, these symptoms come on fast and leave just as quickly. So as soon as you notice these symptoms, if you're able to, McKnight said you should get your dog to a veterinarian and have them take a chest X-ray.

Other times though, these symptoms persist, and the dog can develop pneumonia or other lung problems. These are the sicknesses that can result in death, according to McKnight.

McKnight said that if your dog's cough persists and they start seeming more tired and less interested in food, it could be a sign that they've developed something more serious.

If you haven't already, you should bring your dog to a veterinarian at this point.

Though this illness is something to watch out for, St. Bernard told BI that she wasn't sure this disease is any more deadly than the normal bugs that dogs can catch this time of year.

"I wouldn't panic at this point. I understand mystery illnesses, sounds exciting and scary, and all those things. But lots of illnesses are mysteries. We don't know what causes everything," St. Bernard said.