Foto: BB.LV / кот зимой
When it comes to parasites that cats can potentially transmit to humans, Toxoplasma gondii is often the first that comes to mind. However, there is another microscopic organism that many pet owners know very little about. This is Giardia duodenalis — a single-celled parasite that causes giardiasis. The disease can be asymptomatic but sometimes leads to diarrhea, abdominal pain, weakness, and other health issues. In young animals, the infection can also negatively affect growth and development. Researchers aimed to determine how widespread this parasite is among domestic cats and which animals are at the highest risk of infection. The study was led by veterinarian Margaret Wingerd from the VCA SouthPaws veterinary center in Virginia, USA. Scientists analyzed over 157,000 fecal samples from domestic cats collected in the United States and Canada. According to the authors, this is the largest study to date on the prevalence of Giardia duodenalis among domestic cats in North America. Using PCR testing, the parasite was found in 9,962 samples. Thus, a positive result was obtained in 6.3% of cases — approximately one in every sixteen cats examined. ### Kittens are infected significantly more often One of the most notable findings of the study was the correlation between the frequency of infection and the age of the animal. Among kittens, the parasite was found in 10.7% of samples. For cats aged ten years and older, this figure was only 1.3%. Thus, positive results were found more than eight times more often in young animals.  Researchers suggest that this may be explained by the development of immune protection. As cats age, they acquire immunity to certain infections, which reduces the likelihood of infection. Additionally, kittens may come into contact with sources of infection more frequently due to their behavior and living conditions. Other patterns also emerged. Male cats were found to be infected slightly more often than females, and among adult animals, unneutered and unspayed individuals were more likely to carry the parasite. Possible reasons include more active movements, contacts with other animals, and differences in living conditions. However, the study does not establish which specific factor plays a decisive role. ### Why the parasite is found more often in winter The researchers also discovered pronounced seasonal differences. In summer, Giardia duodenalis was detected in 4.6% of the examined samples, while in winter, it was found in 8.1%. According to the authors, the reason may lie in the parasite's ability to survive in the external environment. Giardia duodenalis forms resilient cysts that can persist for a long time in cool and moist conditions. Hot and dry weather, on the contrary, reduces their survival. This may explain why infections are detected less frequently in summer. At the same time, these results pertain to the study conducted in North America. Local data is needed to assess seasonal risks in Latvia. ### Can a cat infect a human? The researchers paid special attention to the genetic variants of Giardia duodenalis. Not all variants of the parasite are equally dangerous to humans. Some primarily infect animals, while genetic groups A and B have zoonotic potential, meaning they can also infect humans. Among the 9,962 positive samples, such variants were found in 1,840 cases — approximately 18.5% of infected cats. Considering all examined samples, the proportion of potentially dangerous variants for humans was about 1.2%. This is a relatively small figure; however, the authors emphasize that it deserves attention. At the same time, the detection of a potentially zoonotic variant of the parasite in a cat does not necessarily mean that the animal will infect its owner. Giardia is transmitted via the fecal-oral route, particularly through contaminated water, food, and surfaces. ### Which cats should be given special attention The researchers recommend regularly testing the feces of domestic cats, especially if the animal belongs to a high-risk group. Particular attention should be paid to kittens, as well as cats living in households with small children, elderly people, or individuals with weakened immune systems. If an animal shows prolonged diarrhea, a decrease in appetite, weight loss, or other signs of gastrointestinal disease, it should be taken to a veterinarian. To prevent infection, it is important to regularly clean the cat litter box, wash hands after contact with it, and ensure the cleanliness of water and the animals' living areas. The study's authors note that Giardia duodenalis can infect a wide range of hosts, making it a concern not only for veterinary medicine but also for public health. The main conclusion of the study is that even an outwardly healthy cat can be a carrier of intestinal parasites. Moreover, young animals are the most vulnerable, and the likelihood of detecting the infection significantly increases in winter. The results of this large-scale study were published in the scientific journal [PLOS One](https://doi.org/10.1371/journal.pone.0358546).
