Some cats carry Giardia strains that can infect people, but the risk is manageable. A large 2026 study found the parasite in 6.3% of cat stool samples tested across North America, and 18.5% of those infected cats carried strains with the potential to spread to humans.
The good news is that a simple stool test can detect it, and good litter box habits go a long way toward protecting your whole household.
Giardia is a microscopic intestinal parasite that lives in the gut of cats, dogs, people, and other mammals. It spreads through tiny, hardy cysts passed in feces.
A cat becomes infected by swallowing those cysts. That can happen through contaminated water, grooming, contact with other animals, or an unclean litter environment.
In people, the illness is often called "beaver fever." The CDC lists Giardia as one of the most common causes of waterborne intestinal illness in the United States.
Researchers analyzed 157,616 cat stool samples from 49 U.S. states, Washington D.C., and five Canadian provinces. The study was published in PLOS One on October 7, 2026.
Key findings include:
The researchers note an important limit. The study confirms these strains are present in cats, but it did not track whether any cat actually passed Giardia to a person.
Kittens carry the highest risk. Their immune systems are still developing, and they often come from shelters or multi-cat environments with greater exposure.
Other patterns from the study:
That seasonal pattern makes autumn a smart time for Oklahoma cat owners to pay closer attention.
It is possible, but most cats with Giardia carry a cat-specific strain that does not infect people. Only the A and B strains carry zoonotic potential, meaning they can move between animals and humans.
The researchers also raised a two-way possibility. Some cats may have picked up human strains from people in the first place.
Households that should take extra care include those with:
Many cats with Giardia show no signs at all. That is why the study's authors recommend routine stool testing rather than waiting for symptoms.
When symptoms do appear, they may include:
The Merck Veterinary Manual offers additional detail on how Giardia affects the digestive tract in animals.
Most mild diarrhea can wait for your primary care veterinarian. Some signs, however, call for prompt emergency care.
Oklahoma Veterinary Specialists is open 24 hours a day, 7 days a week, 365 days a year. No appointment is needed for emergencies.
Simple daily habits reduce the risk for both pets and people.
Most Giardia cases are diagnosed and treated by your primary care veterinarian. Some cats, however, have digestive symptoms that persist after treatment or point to something more complex.
The board-certified Internal Medicine specialists at Oklahoma Veterinary Specialists work alongside your primary care veterinarian when chronic gastrointestinal disease needs a closer look. Our team uses advanced diagnostics, including abdominal ultrasound, to help find answers when standard testing is inconclusive.
We see ourselves as a partner to your family veterinarian. Together, we focus on getting your cat comfortable and back to their routine.
If your cat is showing signs of a digestive emergency, our Tulsa hospital is here day and night. Call Oklahoma Veterinary Specialists at 918-299-4900 or visit okvets.com to learn more.
Oklahoma Veterinary Specialists delivers 24-hour emergency care and board-certified specialty services with advanced technology and compassionate treatment.
