ABSTRACT
Several members of protozoa belonging to the phylum Apicomplexa are human parasites; they include the genera Plasmodium and Babesia infecting mainly erythrocytes, Toxoplasma and Sarcocystis inhabiting various tissues, and enteric coccidia in the genera Isospora, Cyclospora, and Cryptosporidium mainly involving intestinal epithelial cells. All enteric coccidian protozoa cause indistinguishable gastrointestinal symptoms; therefore, a laboratory investigation is crucial to make de‘nite diagnosis and, as a consequence, a proper management. Isospora belli is the only species pathogenic to humans, causing isosporiasis. I. belli is a coccidian protozoa that parasitizes epithelium cells of human small intestines, causing isosporiasis. Historically, the description of characteristic oocysts of I. belli in stools was initially observed among military personnel stationed in Egypt, the Middle East, and eastern Mediterranean countries during 1914 and 1921 [1]. Nowadays, it is well recognized that isosporiasis has a cosmopolitan distribution. Although oocysts of I. natalensis were reportedly found in human fecal samples, several studies have failed to reaf‘rm the presence of these oocysts as a causative agent of diarrheal illness in humans since its ‘rst report in 1953, raising the possibility that it may not be a valid pathogenic species in humans [2]. Most of the enteric coccidian parasites of man are considered to be opportunistic pathogens except the genus Sarcocystis. Thus, the prevalence of these coccidian infections seems to increase as the number of immunocompromised patients increases, especially after the acquired immunode‘ciency
syndrome (AIDS) becomes pandemic. In general, the severity of illness caused by I. belli seems to be more aggressive in patients with compromised immunity than those with normal immune status. However, chronic emaciating infections have been reported in immunocompetent patients, suggesting that host immunity per se may not determine the severity of isosporiasis [3,4]. Meanwhile, difference in intrinsic virulence of this organism has not yet been explored.
