Biology of Isospora spp. from humans, nonhuman primates, and domestic animals

Abstract

Coccidial parasites of the genus Isospora cause intestinal disease in several mammalian host species. These protozoal parasites have asexual and sexual stages within intestinal cells of their hosts and produce an environmentally resistant cyst stage, the oocyst. Infections are acquired by the ingestion of infective (sporulated) oocysts in contaminated food or water. Some species of mammalian Isospora have evolved the ability to use paratenic (transport) hosts. In these cases, infections can be acquired by ingestion of an infected paratenic host. Human intestinal isosporiasis is caused by Isospora belli. Symptoms of I. belli infection in immunocompetent patients include diarrhea, steatorrhea, headache, fever, malaise, abdominal pain, vomiting, dehydration, and weight loss, blood is not usually present in the feces. The disease is often chronic, with parasites present in the feces or biopsy specimens for several months to years. Recurrences are common, Symptoms are more severe in AIDS patients, with the diarrhea being more watery. Extraintestinal stages of I. belli have been observed in AIDS patients but not immunocompetent patients. Treatment of I. belli infection with trimethoprim-sulfamethoxazole usually results in a rapid clinical response. Maintenance treatment with trimethoprim-sulfamethoxazole is needed because relapses often occur once treatment is stopped.

Taxonomic position of the human intestinal protozoan parasite Isospora belli as based on ribosomal RNA sequences

“…Human isosporiasis is clinically indistinguishable from cryptosporidiosis, giardiasis, cyclosporiasis, and microsporidiosis, and I. belli causes symptoms that may range from mild gastrointestinal distress to serious and sometimes fatal disease in immunocompetent and immunocompromised hosts. I. belli infections are essentially cosmopolitan in distribution but are more common in tropical and subtropical regions, especially Haiti, Mexico, Brazil, El Salvador, tropical Africa, the Middle East, and Southeast Asia (Lindsay et al 1997).…”

“…It is thought to be the only Isospora species infecting humans, which are the organism's only known host, and there is no evidence that I. belli is capable of infecting nonhuman hosts or that animal Isospora spp. infect humans (Ackers 1997;Goodgame 1996;Kirkpatrick and Dubey 1987;Lindsay et al 1997). Sporulated oocysts of Isospora species resemble the sporulated oocysts of the related genera Toxoplasma, Eimeria, and Sarcocystis, which led to much confusion during the period ranging from the late 1800s to the mid-1970s, when the life cycles of these parasites were not known.…”

Determination of the genera of cyst-forming coccidia

“…When the facultative heteroxeny of species was recognized, the genus Cystoisospora was created (Frenkel 1977). Some authors consider the intermediate host to be merely a paratenic host (Lindsay et al 1997), because, contrary to our first impressions ) no multiplication appears to takes place in the paratenic host. However, the biological importance of heteroxeny, and of paratenic or intermediary hosts, is similar.…”

“…C. belli shed in human feces forms unizoic cysts in extra-intestinal tissues of humans, the definitive host (Lindsay et al 1997;Frenkel et al 2003); their intermediate host has not been identified. These species were described originally in the genus Isospora, in the belief that they were monoxenous organisms.…”

Safety of 5% Ponazuril (Toltrazuril sulfone) Oral Suspension and Efficacy against Naturally Acquired Cystoisospora ohioensislike Infection in Beagle Puppies

“…These species are Cystoisospora ohioensis, C. neorivolta and C. burrowsi (Lindsay et al 1997). Because the oocysts cannot be discriminated during routine faecal examination, this species complex is termed "C. ohioensis-like" for diagnostic purposes.…”