A dangerous parasite for humans has been discovered in domestic cats

Your domestic cat may be a hidden carrier of a parasite dangerous to humans. This is the conclusion reached by the authors of a large-scale study, the results of which were published in the scientific journal PLOS One.

Specialists from Antech Diagnostics and Mars Petcare Science & Diagnostics analyzed test data from more than 157,600 domestic cats in the USA and Canada, collected from March 2022 to August 2023.

It was found that 6.3% of cats were carriers of the intestinal parasite Giardia duodenalis. Among the infected animals, 18.5% carried genetic variants of assemblages A or B — precisely the ones capable of being transmitted from animals to humans. The vast majority of cases, however, involved strains characteristic of cats, particularly assemblage F, which generally does not pose a threat to humans.

Giardia duodenalis, more commonly known as giardia, is a microscopic parasite that inhabits the intestines of humans and animals. Most often it coexists peacefully with its host, showing no symptoms whatsoever. However, when it transitions to a pathogenic form, it can cause diarrhea, digestive disorders, and weight loss.

Giardia is found worldwide and is transmitted through contaminated water, food, objects and surfaces, as well as through direct contact between people. In the USA, the parasite is detected in 1.4% of the population. In animals, the picture is even more varied: infection rates range from 3.7% to 100% in cattle, from 1.1% to 56.8% in dogs, and from 0.2% to 44.4% in cats.

In 2023, scientists proposed dividing Giardia into eight separate species — from A to H. Most of them are tied to specific hosts: C and D affect dogs, E — ungulates, F — cats, G — rodents, H — pinnipeds. Assemblages A and B stand apart — they infect humans and a wide range of other mammals, making them the primary threat to public health.

The cat's age turned out to be a key risk factor. In kittens, the infection rate reached 10.7%, while in elderly cats it was only 1.3%. At the same time, among infected kittens, approximately one in five carried types A or B, which are potentially dangerous to humans.

Geography and time of year also played a significant role. The lowest infection rates were recorded in summer (4.6%), while the peak occurred in winter (8.1%) and autumn (7.7%).

The study authors recommend that cat owners — especially families with young children, elderly individuals, or relatives with weakened immune systems — regularly have their pets' feces tested. Identifying the specific Giardia assemblage will allow veterinarians to make more precise treatment decisions and more effectively protect the health of the entire family.