Blastocystosis

Blastocystis , the causative agent of blastocystosis, is an intestinal protozoan commonly identified in stool specimens of patients. It is one of the most common parasites inhabiting the human intestinal tract. Clinical symptoms attributed to Blastocystis include recurrent watery diarrhoea, mucous diarrhoea, vomiting, abdominal cramps and flatulence. Blastocystis infects both children and adults and its geographical distribution appears to be global with prevalence ranging from 30 to 50% in developing countries (Stenzel and Boreham 1996).Blastocystis was first described as a distinct organism in 1911 and the name B. enterocola was proposed for this organism (Alexeieff 1911). It was isolated from human faeces and the name B. hominis was coined (Brumpt 1912). At first, it was described as a harmless intestinal yeast and ignored for many decades. Its association with human disease was suggested by a number of reports and eventually work by Zierdt (1991) increased the awareness of Blastocystis infections in humans.In spite of its description about a century ago, the exact role of Blastocystis as a cause of human disease is uncertain. A number of clinical and epidemiological studies implicate the parasite as a potential pathogen (Al-Tawil et al. 1994; El-Shazly et al. 2005; Garavelli et al. 1991; Logar et al. 1994) while others exonerate it as an etiology of intestinal disease (Chen et al. 2003; Leder et al. 2005; Shlim et al. 1995). Significant progress has been achieved on descriptions of the morphology and genetic diversity of Blastocystis but most aspects of its life cycle, molecular biology, and athogenicity remain unresolved (Stenzel and Boreham 1996; Tan 2004).