Tritrichomonas foetus is a sexually transmitted protozoan. It is responsible for most recurrent diarrhea in cats. T. foetus is present in the large intestine in the form of active trophozoites (developmental stage) that are excreted in the feces of the sick animal. Only in freshly cut faeces it is possible to identify the presence of trophozoites. The infection occurs by gastrointestinal route during contact with faeces from sick cats. Parasites do not produce cysts. It is believed that the main reservoir of parasites are infected cats being asymptomatic carrier. T. fetus infections in cattle are responsible, among others, for miscarriage, uteritis and infertility. The microorganism can cause intestinal inflammation associated with difficult to treat and prolonged diarrhea. Thickening of the intestinal mucosa can be seen in the ultrasound examination. From a histological point of view it is not possible to distinguish the inflammatory bowel disease caused by this protozoa from other inflammatory conditions.