Many people with pets can relate — on sick days, their dog or cat seems to know something is wrong. More so, they refuse to leave their side. They follow them from the bed to the couch and back again.

When pets keep close to their ailing humans, researchers have found it is possible to pass on the pathogen. Although scientists typically focus on animal-borne diseases that spread to humans (like the Avian flu), researchers are increasingly considering how diseases can spread in the reverse.

Scientists are finding that passing pathogens from humans to animals can result in strain mutations that have the possibility to reinfect humans. Researchers are calling for more attention to an understudied but possibly problematic topic. 

Reverse Zoonoses

Zoonosis is when a disease spreads from animals to humans. When pathogens spread from human to animals, it’s called reverse zoonoses. The transmission can happen through a variety of forms including bacterial, parasitical or viral.

Pathogens can spread through direct contact as well as airborne particles. It’s also possible for transmission to occur environmentally. An animal, for example, could come into contact with a pathogen in the soil. Vectors such as ticks can also pass on diseases from one infected host to another.

Read More: What is Zoonoses? Can Our Cats and Dogs Actually Give Us Diseases?

Reverse Zoonoses Could be a Problem

Scientists are concerned about reverse zoonoses for two main reasons. First, animals can be harmed by the illness. And second, it’s possible for the pathogen to mutate and then be transmitted back to humans.

Cats, for example, can get human diseases like Influenza A. There are an estimated 600 million domesticated cats globally. An influenza outbreak among cats could be devastating to the feline population. It could also be harmful if the pathogen mutated and passed back to humans as a treatment-resistant strain. 

Read More: Self-Spreading Animal Vaccines Could Combat Human Pandemics

Diseases From Reverse Zoonoses

Besides Influenza A, there are other types of reverse zoonoses including Ascaris lumbricoides (a type of roundworm); Cryptosporidium parvum (a water-borne pathogen that affects the small bowel); and methicillin-resistant Staphylococcus aureus (MRSA, an antibiotic-resistant staph infection). 

Pandemics like the 1918 Flu and the recent COVID-19 outbreak derived from a zoonotic and reverse zoonosis process. Even though the consequences were globally devastating, scientists have primarily focused on the zoonosis process.

A 2014 literature review in Plos One, examined scientific studies relating to reverse zoonoses and found only 56 examples in the previous decades. The authors concluded that reverse zoonoses are a global threat and more research and attention is needed.

Read More: Can Your Pets Get Coronavirus, and Can You Catch It From Them?

How Viruses Jump from Humans to Animals

Although research into reverse zoonosis has been limited in the past, scientists do have an understanding of how disease spreads from humans to animals.

When a person is infected with a flu virus, for example, the virus enters and then binds itself to a protein called a receptor found on the outside of cells. The virus then injects its material into the cell and replicates.

Whether a virus can bind to a receptor in human and animal cells depends on the type of virus. “In the case of the flu, we know there are some strains that are able to bind to human receptors, canine receptors, and or feline receptors,” says Benjamin D. Anderson, an assistant professor in the College of Public Health and Health Professions at the University of Florida and a member of the Emerging Pathogens Institute.

Read More: Does Munchausen Syndrome Exists in Pets?

Can I Get My Pet Sick?

Depending on the virus, people can get their pets sick. However, Anderson says the symptoms will not be the same. “That has to do with the immune system of the animal and how efficiently that virus can bind,” Anderson says. “Maybe the virus can bind, but it might not bind as efficiently or replicate.” 

If the virus can bind and replicate, Anderson says it has the ability to mutate. The mutation can change the way the virus functions, which means it could be passed back to humans.

“This is the greatest concern we have,” Anderson says.

Read More: Can Dogs Get Sick? How to Keep Your Dog Healthy

Keeping Your Pet Safe

When a person is sick, keeping their pet safe can be as simple as treating them like they were, well… human. Anderson says that people wouldn’t cough or sneeze directly onto friends or family members. They also wouldn’t get too close and they would keep a safe distance until healed.

The same should apply to pets. Although people should still provide care and affection, they should refrain from behaviors like smooching a dog’s face or booping a cat’s nose. People should also wash their hands before feeding the animal. 

And if their animal shows signs of being unwell, Anderson says it’s important to see a veterinarian and let them know about the recent illness in case it needs to be tied to a larger outbreak. 

Read More: How to Tell if Your Cat Is Sick

An Increasing Threat 

Scientists consider reverse zoonoses an increasing health threat. “The number of people who are interacting with animals is greater,” Anderson says. “Not just with domestic pets, but we also have a greater variety of domestic pets. People have dogs and cats but also pet ‘fill-in-the-blank.’” 

Exotic pets mean there is greater diversity in the types of animal-human contact. Another layer to the potential problem is that Anderson says some exotic pet owners give up on their pets and release them into the wild. Although they aren’t native species, some survive and have the potential to introduce new pathogens into the environment.

“We see this in my home state of Florida,” Anderson says. “ If you look in the Everglades, invasive species in the Everglades are traced back to people who had them as pets.” 

It’s another reason Anderson and other researchers say that although zoonosis is an important topic, reverse zoonosis needs attention, too. 

Read More: Watch an Epidemiologist’s Take on Zoonotic Disease and COVID-19

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

Emilie Lucchesi has written for some of the country’s largest newspapers, including The New York Times, Chicago Tribune and Los Angeles Times. She holds a bachelor’s degree in journalism from the University of Missouri and an MA from DePaul University. She also holds a Ph.D. in communication from the University of Illinois-Chicago with an emphasis on media framing, message construction and stigma communication. Emilie has authored three nonfiction books. Her third, “A Light in the Dark: Surviving More Than Ted Bundy,” releases October 3, 2023 from Chicago Review Press and is co-authored with survivor Kathy Kleiner Rubin.