The Ciliophora’s group of protozoan parasites are most commonly known as ciliates. The term cilia refer to hair-like structures present in a large number at the surface of the parasite and involved in the motility. The total number of existing ciliates parasites are estimated to be up to 30 000 species, but Balantidium coli is the only known species able to parasitize humans. It is also considered as the largest protozoan parasite able to infect humans.
Human is therefore considered as an accidental host for Balantidium coli, meaning that it is not a normal host for this parasite. As such, this type of infection is considered to be quite rare. The usual animal hosts for this protozoan parasite include notably pigs, but also other wild animals, such as wild boars or non-human primates. Transmission of the disease to human is mostly due to the ingestion of parasites’ cysts in water contaminated with pigs’ faeces. Very close contacts between pigs and humans can also contribute to the disease propagation. As such, the human infection, called balantidiasis, is considered to be a zoonotic disease. In some endemic area, water contaminated with faeces from infected individuals can also contribute to the transmission of the disease.
The parasite is present worldwide, but is especially a problem in developing countries with poor water sanitation. This disease is particularly common in the Philippines, in Bolivia and in Papua New Guinea, particularly in areas where people almost cohabit with pigs. This disease is also more common in people with weaken immune system or suffering from malnutrition, because their stomach is usually less acid than others. Actually, the normal stomach acidity of healthy individuals can be able to prevent the disease by the destruction of the ingested cysts.
Balantidiasis is usually asymptomatic because of a certain balance established between the parasite and the normal human’s flora during the time that the parasite adapts to its unusual host. However, symptomatic form of the disease is very severe, including explosive diarrhoea leading occasionally to dysentery. It can also be life-threatening if the colon is perforated during the acute phase of the disease.
Diagnosis is made from the presence of parasites in the faeces or in tissues collected during a colonoscopy. However, as this parasite is not frequent in human, it could take a while to obtain a proper diagnosis. Furthermore, this disease is usually treatable using anti-parasitic drugs.
Source: Centers for Disease Control and Prevention