Submitted to: Journal of Eukaryotic Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2002
Publication Date: 12/31/2002
Citation: Morgan-Ryan, U.M., Fall, A., Ward, L.A., Hijjawi, N., Sulaiman, I., Fayer, R., Thompson, R., Olson, M., Lal, A., Xiao, L. 2002. Cryptosporidium hominis n. sp. (Apicomplexa: Cryptosporididae) from humans, homo sapiens. Journal of Eukaryotic Microbiology. 49(6):433-440. Interpretive Summary: Parasites of the genus Cryptosporidium infect reptiles, birds, and over 150 species of mammals including food animals and humans, often causing diarrheal illness and sometimes death. Identification of species has been difficult because the stage found in the environment, the fecally transmitted oocyst stage, is virtually identical from species to species. Identification, important for determining the source of the parasite and other potential hosts, requires testing for genetic traits. Those found with unique genotypic traits also possess unique biological traits such as infectivity for humans or some animal species but not others. The present study clearly distinguishes the parasite that specifically infects humans and rarely infects other animals from all other species of Cryptosporidium on the basis of genetic and biological characteristics and proposes the name of a new species- Cryptosporidium hominis.
Technical Abstract: The structure and infectivity of the oocysts of a new species of Cryptosporidium from the feces of humans are described. Oocysts are structurally indistinguishable from those of Cryptosporidium parvum. Oocysts of the new species are passed fully sporulated, lack sporocysts, and measure 4.6 - 5.4 m (mean = 5.0) X 3.8 - 4.7 m (mean = 4.3 m) with a length to width ratio 1.16 (n=50). Oocysts were not infectious for ARC Swiss mice, nude mice, Wistar rat pups, puppies, kittens or calves, but were infectious to neonatal gnotobiotic pigs. Pathogenicity studies in the gnotobiotic pig model revealed significant differences in site of infection and oocyst output between C. parvum and this newly described species from humans. In vitro cultivation studies have also revealed growth differences between the two species. Multi-locus analysis of numerous unlinked loci, including a preliminary sequence scan of the entire genome demonstrates this species to be distinct from C. parvum and also demonstrates a lack of recombination, providing further support for species status. Based on biological and molecular data, this Cryptosporidium infecting the intestine of humans is a new species and the name Cryptosporidium hominis n. sp. is proposed for this parasite.