PARASITOLOGYBlastocystis and its pathogenic potential: latest aspectsVassalos, Constantine Ma,b; Vakalis, Nicholasa; Papadopoulou, Chryssanthyb Author Information aDepartment of Parasitology, Entomology and Tropical Diseases, National School of Public Health, Athens, Greece bDepartment of Microbiology, Medical School, University of Ioannina, Ioannina, Greece. Received 24 January, 2009 Accepted 26 January, 2009 Correspondence to Constantine M. Vassalos, Department of Parasitology, Entomology and Tropical Diseases, National School of Public Health, Alexandras Avenue, 196, GR-115 21, Athens, Greece. Tel: +30 6972025952; fax: +30 2107625322; e-mail: [email protected] Reviews in Medical Microbiology 19(4):p 87-97, October 2008. | DOI: 10.1097/MRM.0b013e32832d87ec Buy Metrics Abstract Blastocystis is a ubiquitous intestinal protozoan isolated from human and other animals and is frequently found in human stools. Various morphological forms and wide genetic diversity have been observed. Research results have been gradually unraveling the conundrums of parasite's life cycle and pathogenicity. The presence of amoeboid forms in Blastocystis xenic culture might facilitate checking for possible pathogenic isolates between or within subtypes, probably under specific conditions. This review focuses on the latest aspects in Blastocystis pathogenicity in association with interspecific or intraspecific variation. We also focus on differences in morphology, surface properties and between amoeboid and nonamoeboid forms and other putative virulence factors. Asymptomatic infections have been reported; immunocompromised individuals might have diarrhoeal disease related to Blastocystis; and immununocompetent patients with Blastocystis might present with irritable bowel syndrome-like symptoms, skin and other extraintestinal manifestations. Drug susceptibility testing is not currently available; metronidazole is the drug of choice, but resistance has developed. Other therapeutic options include nitazoxanide and trimethoprim–sulfomethoxazole. Paromomycin was reported to be successful in treating urticarial manifestations of Blastocystis infection. Further investigations are required to study virulence regulation at genetic level or by other host factors and to identify new targets for drugs. © 2008 Lippincott Williams & Wilkins, Inc.