A parasite that can cause digestive problems in both cats and humans has been detected in thousands of feline samples across North America. A large new study suggests that Giardia duodenalis is more common in cats than many families might realize, with approximately one in fifteen cats testing positive. Researchers also identified strains with the potential to infect humans, raising important questions about household hygiene, early detection, and how cat parents can protect their pets without becoming unnecessarily worried about everyday companionship.
The findings come from an extensive investigation involving more than 150,000 feline samples collected across 49 U.S. states and five Canadian provinces. While the results deserve attention, veterinarians emphasize that Giardia infections are generally treatable and that simple preventive habits can help reduce exposure.
What Researchers Discovered About Giardia in Cats
The study, published in the scientific journal PLOS ONE, examined samples for Giardia duodenalis, a microscopic intestinal parasite that can infect animals and people. Researchers found evidence of infection in approximately 6.7 percent of the cats tested.
Among infected cats, roughly one in five carried forms of Giardia with the potential to infect humans. However, this does not mean that one in five infected cats will actually transmit the parasite to a person.
Dr. Anne Kimmerlein, a study coauthor and Global Veterinary Epidemiologist at Mars Veterinary Health, explained to ABC News that understanding how frequently Giardia occurs can help veterinarians recognize infections earlier and guide families toward appropriate treatment and prevention.
The findings are especially relevant because cats do not always show obvious signs of infection. A cat may appear healthy while carrying the parasite, making hygiene and veterinary attention important even when everything seems normal.
Which Cats Are More Likely to Become Infected?
Researchers identified several factors associated with higher rates of Giardia infection. Kittens were more likely to test positive than adult cats, while male cats showed higher infection rates than females.
Neutered kittens also had a noticeably greater likelihood of infection. Researchers suggested that this association might reflect exposure in shelters and rescue environments, where young cats may have more opportunities to encounter infected animals.
Geography and seasonal conditions appeared to matter as well. Cats in the Midwestern United States had higher infection rates than cats in other regions, although environmental differences and testing patterns may help explain those findings.
Giardia was detected less frequently during summer. Researchers noted that the parasite can survive more readily in cool, moist environments, potentially contributing to seasonal differences.
These patterns do not mean that every kitten, shelter cat, or male cat is infected. They simply identify groups in which positive test results were more common.
How Giardia Spreads and What Symptoms to Watch For
Giardia lives in the intestines of infected animals and humans and spreads through fecal contamination. Infection can occur when someone accidentally swallows the parasite after contact with contaminated water, surfaces, or other materials.
The parasite is sometimes called “beaver fever,” a nickname that became popular following waterborne outbreaks associated with areas inhabited by beavers. Infected cats may develop diarrhea and other digestive problems, although some show no symptoms. In humans, Giardia can cause frequent diarrhea, stomach discomfort, bloating, and other gastrointestinal symptoms.
According to the Centers for Disease Control and Prevention, symptoms in humans typically begin one to two weeks after exposure. Many infections resolve within several weeks, but some people experience longer-lasting complications.
Young children and people with weakened immune systems may face additional risks. However, the presence of Giardia in a household cat does not automatically mean that family members will become infected.
The CDC also notes that people are generally unlikely to acquire Giardia directly from their cats or dogs because the types that commonly infect people are often different from those found in pets.
Simple Ways Cat Parents Can Reduce the Risk
Veterinarians recommend maintaining clean litter boxes, washing hands after handling cat waste, and keeping food and water bowls clean. These everyday practices help reduce opportunities for parasites to spread.
Dr. Stevie Aitken, an emergency veterinarian interviewed by ABC News, emphasized thorough cleaning when a cat receives a Giardia diagnosis. This includes litter boxes, feeding equipment, and areas where accidents may have occurred.
Families with young children or immunocompromised household members may need additional precautions. Aitken also recommended discussing more frequent screening with a veterinarian when household circumstances warrant it.
If a cat develops persistent diarrhea or other concerning digestive symptoms, a veterinarian can determine whether testing is necessary. Treatment may involve prescribed medication along with cleaning measures intended to reduce reinfection.
For cat parents, the findings offer a reason to stay attentive rather than alarmed. Giardia is a recognized and usually treatable infection, and understanding how the parasite spreads can help families respond appropriately.
A clean litter box, regular veterinary care, and careful handwashing remain practical ways to protect the health of cats and the people who love them.