Blastocystis: A Mysterious Disregarded Parasite

Abstract

Blastocystis is anaerobic protozoal parasite colonizing the intestinal tract of humans and many animals. It still has not been elucidated whether it is a commensal organism or a pathogen. Its prevalence varies both between the countries, and between certain population groups within individual countries. Due to poor hygienic conditions, common exposure to animals and intake of contaminated water and food, people in the developing countries have got a higher prevalence of Blastocystis but developed countries have not been spared either. 22 subtypes of Blastocystis have been so far identified, but only 10 subtypes were identified in humans. The parasite is transferred by the fecal-oral route. A variety of hosts have been identified, and animal-to-human transmission and vice versa have been documented. Blastocystis is polymorphic with only few of forms such as vacuolar, granular, amoeboid, and the cyst form being commonly known. It has been associated with the irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and urticaria. The diagnosis can be made using the microscopy, staining, cultivation, serodiagnosis, and by using molecular methods. The infection caused by the parasite does not always require treatment. In symptomatic patients, the first line medical treatment is metronidazole.