Which protozoal parasite is associated with chronic diarrhea in cats?

• A. Giardia lamblia
• B. Coccidia
• C. Tritrichomonas foetus
• D. Histoplasma

Answer: (C)

Chronic large-bowel diarrhea in cats is most characteristically linked to Tritrichomonas foetus, a flagellated protozoan that colonizes the colon and produces persistent loose stools, often with mucus and frequent straining, especially in young indoor cats. This organism spreads by fecal-oral contact and is commonly seen in cats sharing litter boxes or living in close proximity. Because the parasite can be shed intermittently and be difficult to detect on a single stool test, diagnosis usually relies on stool culture or PCR testing, or specialized methods like InPouch TF culture, rather than quick smear exams.

Treatment centers on clearing the infection, with ronidazole being the drug of choice, though it requires careful dosing due to potential neurotoxicity and other side effects. Environmental control, including diligent litter box hygiene and cleaning, helps reduce transmission and reinfection.

Other protozoa like Giardia lamblia can cause diarrhea in cats, but it is less specifically associated with the chronic large-bowel diarrhea pattern seen in many feline cases. Coccidia can cause diarrhea, particularly in kittens, but it’s not the typical cause of chronic diarrhea in adult cats. Histoplasma is a fungus, not a protozoan parasite, and thus not the correct association here.