Can you catch a hidden virus from a dog kiss or a cat cuddle?

"Get ready for a silly question," one reader wrote in response to our series on "hidden viruses" that jump from animals to people.

"I love my pups very much – and I think they love me too because I get lots of kisses. Is that bad from a spillover virus perspective – for me or my dogs? Should I train my pups to be less ... kissy? That's gonna be tough. I may just accept the risk :)"

This question isn't silly, at all. The vast majority of time that you get sick, you''re infected by another human. But that's not always the case. You can absolutely catch viruses from your pets, including dogs and cats.

And it isn't just from getting pet kisses. If you're physically close with your dog or cat – like snuggling on the couch together or sleeping in the same room, you're exposed to their viruses even without the saliva directly on your face. So kissing isn't really adding that much more exposure.

One virologist tried to figure out what new viruses his own cats might be carrying. "One of them likes to sleep on my head," says John Lednicky, who's at the University of Florida.

And he wasn't disappointed.

For years, Lednicky had a cat named Gibbs. "He was named after the singer Barry Gibb." And Gibbs loved to bring Lednicky "gifts."

"He used to bring me presents every single day. Rodents. Half-eaten rabbits. Snakes, birds, frogs. He was also making friends with opossums, too. So who knows what viruses my cat might be bringing into our home."

Lednicky's cat had a few ticks. "My backyard is full of raccoons and deer, which carry ticks," he says. He plucked a few ticks off the cat and took them into his lab and looked to see what viruses lurked inside.

"I pulled out Heartland virus from the ticks," he says. Scientists first identified Heartland virus back in 2012 in Missouri. Although thought to be rare in the U.S. the virus can cause a serious illness that can require hospitalization.

According to the Centers for Disease and Prevention, the U.S. has recorded about 60 cases of Heartland virus – and none in Florida. But Lednicky thinks some people in the state have probably caught Heartland, perhaps from ticks on their pets. "It's probably been diagnosed as a flu or something else," he says. Lednicky doesn't think Heartland is a major concern in Florida. He just thinks it's a bit more widespread than previously thought. "Just because I found it doesn't mean it's a problem." It just means some cases are going undetected.

Of course, dogs carry ticks, too. And they can also carry some interesting viruses.

As we explained in a previous article in our series, scientists think a new coronavirus – found in Arkansas, Haiti, Malaysia and Thailand – likely jumps from dogs into people.

"The virus probably circulates widely around the world, but no one has paid attention to it," Lednicky says. And if you've been around dogs frequently, he says, you might have caught this virus, which has a very technical name: CCoV-HuPn-2018.

But that doesn't mean you necessarily fell ill. The vast majority of time, these viruses from your pets don't make you very sick or even sick at all. For example, the new coronavirus that Lednicky cited may cause pneumonia in younger children but, in adults, it causes only mild symptoms, which resemble a cold or mild flu, or no symptoms at all. So you wouldn't probably even realize your dog infected you.

And as Lednicky points out, being exposed to viruses from your dogs, such as the new coronavirus, probably gives you immunity to that virus and similar ones.

Also, what viruses your pets have depends largely on their behavior. If your cat or dog is a homebody, who eats mostly from a can or bag stored in the kitchen, then they will likely not be infected with Heartland virus or some other exotic virus – except, that is, for the viruses you bring into the home.

Yes, we spill over our viruses to animals all the time, Lednicky says. It's called reverse spillover or reverse zoonosis. People don't realize how often we, the humans, pass along viruses to our pets, Lednicky says. "We don't understand reverse zoonosis well."

Take for instance, he says, what happens to cats after graduate students have parties at the University of Florida.

"I hear the same story over and over again from grad students: 'We had a party and my cat is now hiding in the closet," Lednicky explains, seemingly because the large number of people freaked out the cat.

"I always ask, 'How do you know your cat's not sick?' Sick cats hide because they don't want other members of the species to see them as weak."

And so, finally, Lednicky tested his hypothesis. He took samples from a hiding cat and tested it. "The cat turned out to have influenza virus – a human influenza." [Copyright 2023 NPR]