This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Giardia duodenalis is a microscopic, flagellated parasite that often calls the human and animal gut its home. In most cases, it coexists harmlessly with its host, and most infected pets and people show no signs of illness.
However, when it becomes pathogenic, it can cause diarrhea, digestive issues or weight loss. Cats can carry a pathogenic version of the gut parasite that also infects humans, but how common is it among pet cats, and how often do they harbor such strains? A recent study investigated these questions by analyzing stool test data from 157,616 pet cats across 49 U.S. states and five Canadian provinces between March 2022 and August 2023.
The results showed that 6.3% of the cats tested positive for Giardia duodenalis. Among the infected cats, 18.5% carried assemblages A or B, genetic groups that can infect both humans and animals. The remaining majority carried strains associated primarily with cats, particularly assemblage F, which generally do not pose a risk to humans.
Giardia duodenalis has found its way across the globe and can hitch a ride through contaminated water, food, surfaces and objects, or pass directly from one person to another. Once inside the small intestine, it sheds its protective shell and starts multiplying, splitting into two. As the parasites grow in number, they begin absorbing nutrients from their host.
In the U.S., the parasite shows up in 1.4% of people. Among animals, reported infection rates range from 3.7% to 100% in cattle, 1.1% to 56.8% in dogs and 0.2% to 44.4% in cats. A 2023 study proposed splitting Giardia into eight separate species, labeled A through H.
Most show clear host preferences: C and D favor dogs, E hoofed animals, F cats, G rodents and H pinnipeds such as seals. Assemblages A and B break the pattern, infecting humans along with a wide range of other mammals, making them the most important for public health. Earlier research on Giardia in cats relied on small sample sizes or focused on very specific locations, such as individual shelters or a few select states.
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