Balantidium coli is a type of large ciliated protozoan, and notably, it's the sole ciliate known to cause infections in humans. Its primary host reservoir is commonly found in swine.

Cysts play a crucial role in transmitting balantidiasis. These cysts are typically acquired by the host through consuming contaminated food or water. Once ingested, they undergo excystation within the small intestine, leading to the colonization of the large intestine by trophozoites. These trophozoites take residence in the large intestine and sometimes the appendix of both humans and animals. Inside these intestines, they undergo replication through binary fission, with a possibility of conjugation. Eventually, the trophozoites transform into cysts, which are the infective form.

While some trophozoites may invade the colon wall, causing ulcers, others return to the intestine's lumen and disintegrate. Mature cysts are then excreted in feces, completing the cycle of transmission.


  • Worldwide
  • Pigs are the primary reservoir
  • Human infections occur more frequently in areas where pigs are raised and sanitation is inadequate.

Clinical Findings

The majority of cases show no symptoms. However, when symptoms do arise, they can either be sudden or long-lasting, leading to abdominal discomfort. In prolonged infections, complications like diarrhea or dysentery may arise. For individuals already weakened or with compromised immune systems, these symptoms can be quite severe and, in some cases, fatal.

While it's uncommon, infections outside the intestines can be serious and occur as a result of the initial intestinal infection. Instances of peritonitis or liver abscesses have been observed, usually stemming from intestinal perforation or the rupture of severe colonic ulcers. Infection of the urogenital tract may occur due to contamination from the anal area or through fistulae formed by severe infection.



Laboratory diagnosis

The diagnosis of Balantidium coli infection relies on identifying trophozoites in stool samples obtained from individuals displaying symptoms or in tissues collected during endoscopic procedures. Cysts are less commonly found and are more likely to be detected in well-formed stool samples.

Balantidium coli cysts are not consistently passed in stool and are quickly degraded once outside the colon. Therefore, multiple stool samples should be collected and promptly examined or preserved to improve the chances of detecting the parasite. Concentration methods like sedimentation or flotation can enhance the likelihood of recovering the parasite. While Lugol's iodine staining is occasionally used for visualization, it might obscure some internal morphological details of the organism.

Prevention and control

  • Follow standard safety procedures
  • Using appropriate personal protective equipment (PPE)
  • Working within a biosafety cabinet

These precautions are necessary to prevent accidental exposure to cysts present in unfixed stool specimens, as these cysts have the potential to be infectious to laboratory personnel.