Cats live in nearly 80 million American households, but a new study suggests nearly one out of fifteen cats are infected with a common parasite, and one out of five infected cats can transmit it to humans.
In the study, published in PLoS One, researchers tested over 150,000 samples from cats in 49 states and five Canadian provinces for Giardia duodenalis, a gastrointestinal parasite found in the United States that can cause frequent diarrhea in both animals and humans.
"Because some strains of Giardia can affect both animal and human health, understanding how commonly it occurs can help support earlier detection, appropriate treatment, and conversations about practical steps pet owners can take to help protect both their pets and their households," Dr. Anne Kimmerlein, co-author of the study and Global Veterinary Epidemiologist at Mars Veterinary Health, told ABC News.
Giardia duodenalis, commonly known as "beaver fever," is a parasite that can infect both humans and animals. The nickname became popular in the 1970s after outbreaks were linked to contaminated water in areas where beavers lived.
Giardia can cause diarrhea up to five times daily, along with other symptoms such as upset stomach and bloating, according to the Centers for Disease Control and Prevention (CDC). Infected pets may exhibit similar symptoms, or no symptoms at all.
Severe cases can cause long-term symptoms lasting years, such as joint inflammation, irritable bowel syndrome, chronic diarrhea or nutritional deficiencies, according to the CDC.
Individuals with vulnerable immune systems, such as children, are at increased risk of complications.
Giardia live in the intestines of infected people and animals and spread through their stool.
Only a few parasites are needed to make an individual sick, which allows it to spread very easily.
Humans are most often infected after drinking unclean water or being in close contact with the fecal material of infected individuals or pets.
Symptoms generally begin one to two weeks after exposure and resolve in under six weeks.
Giardia infections can sometimes resolve on their own without treatment, particularly in people with mild or no symptoms.
However, doctors may prescribe medication and supportive therapy for people with persistent symptoms, those at higher risk of complications or those at risk of spreading the infection to others.
In pets, veterinarians may also prescribe medicine.
"If your cat is diagnosed with Giardia, thoroughly cleaning all litter boxes, water and food bowls is imperative. Clean any areas that accidents may have occurred and keep them separated from young children or immunocompromised individuals until treatment and re-testing is complete," Dr Stevie Aitken, an emergency veterinarian, told ABC News.
Some cats may be more likely than others to become infected with Giardia, possibly due to differences in environmental exposures or behavior.
Researchers found that kittens were more likely to test positive than older cats, and male cats were more likely to be infected than female cats.
Neutered kittens, more often seen in shelters where neutering happens at a younger age, also had a markedly higher likelihood of infection, which may be due to exposure to other rescue animals.
Where a cat lives and the time of year may also play a role. Giardia was detected less often during the summer months, which researchers said may be because the parasite survives better in cooler and moist conditions.
Cats in the Midwest also had higher rates of infection compared with cats in other parts of the United States, which researchers believe may be due to differences in environment and reporting.
Researchers found that some of the same factors linked to a higher chance of infection were also associated with carrying forms of Giardia that may be able to infect people.
Because Giardia is easily spread and can infect humans and animals alike, it has the potential to spread among many humans and animals quickly.
Aitken believes routine testing annually during pet wellness visits or when symptomatic is sufficient but recommends more frequent screening if there are young children or immunocompromised individuals in the house.
"Giardia, while prevalent and occasionally problematic, is typically very treatable. Wash your hands, don't let animals lick your face or your mouth, and keep kids away from litter boxes. And if you're ever concerned about exposure or your cat's health, call your veterinarian," Aitken said.
Dr. Allen Chang is a Geriatric Medicine subspecialist at Dalhousie University and a member of the ABC News Medical Unit.