Cryptosporidium hominis

Cryptosporidium hominis, along with Cryptosporidium parvum, is among the medically important Cryptosporidium species.[1] It is an obligate parasite of humans that can colonize the gastrointestinal tract resulting in the gastroenteritis and diarrhea characteristic of cryptosporidiosis. Unlike C. parvum, which has a rather broad host range, C. hominis is almost exclusively a parasite of humans. As a result, C. hominis has a low zoonotic potential compared to C. parvum. It is spread through the fecal-oral route usually by drinking water contaminated with oocyst laden feces.[2] There are many exposure risks that people can encounter in affected areas of the world. Cryptosporidium infections are large contributors of child death and illness in heavily affected areas, yet low importance has been placed on both identifying the species and finding more treatment options outside of nitazoxanide for children and AIDS patients.[3]

Cryptosporidium hominis
Scientific classification
Kingdom: Chromista
Subkingdom: Harosa
Infrakingdom: Halvaria
Superphylum: Alveolata
Phylum: Apicomplexa
Class: Conoidasida
Subclass: Coccidia
Order: Eucoccidiorida
Suborder: Eimeriorina
Family: Cryptosporidiidae
Genus: Cryptosporidium
Species:
C. hominis
Binomial name
Cryptosporidium hominis
Morgan-Ryan, Fall, Ward, Hijjawi, Sulaiman, Fayer, Thompson, Olson, Lal and Xiao, 2002

Characteristics

C. hominis shares many similar characteristics with C. parvum including identical oocyst morphology and life-cycle. The different cryptosporidium species share nearly identical morphological features, so differentiation is only seen at the molecular level.[4] As a result, C. hominis is most easily differentiated from C. parvum through genetic analysis via time-intensive PCR-restriction fragment length polymorphism or gene sequencing.[5]

Life cycle

The life cycle of Cryptosporidium hominis is similar to that of others of the genus with infective sporozoites from ingested oocysts invading gut epithelium. From there, they undergo merogony and generate merozoites, which escape and can reinvade additional cells and form a secondary meront. The secondary meront then releases secondary merozoites which reinvade and undergo gametogony forming micro and macrogametocytes. The gametocytes can then fuse, forming a zygote, which starts the cycle again.

Treatment

Though symptoms in most immunocompetent persons will resolve without treatment, nitazoxanide has been approved for treatment of diarrhea resulting from cryptosporidiosis. The effectiveness of nitazoxanide in immunocompromised patients, however, is uncertain and current treatments revolve around boosting the host immune system to aid in symptom resolution.[6] Current avenues for treatment include scanning the Cryptosporidium hominis genome for possible targets for vaccine development.[7]

References
  1. Leoni F, Amar C, Nichols G, Pedraza-Díaz S, McLauchlin J (June 2006). "Genetic analysis of Cryptosporidium from 2414 humans with diarrhoea in England between 1985 and 2000". J. Med. Microbiol. 55 (Pt 6): 703–7. doi:10.1099/jmm.0.46251-0. PMID 16687587. Archived from the original on 16 April 2013.
  2. Fayer R (December 2004). "Cryptosporidium: a water-borne zoonotic parasite". Vet. Parasitol. 126 (1–2): 37–56. doi:10.1016/j.vetpar.2004.09.004. PMID 15567578.
  3. Sparks, H.; Nair, G.; Castellanos-Gonzalez, A. & White, A. C. (2010). "Treatment of Cryptosporidium: What We Know, Gaps, and the Way Forward". Current Tropical Medicine Reports. 2 (3): 181–187. doi:10.1007/s40475-015-0056-9. PMC 4640180. PMID 26568906.
  4. Power, M. L.; Holley, M.; Ryan, U. M.; Worden, P.; Gillings, M. R.; et al. (2011). "Identification and differentiation of Cryptosporidium species by capillary electrophoresis single-strand conformation polymorphism". FEMS Microbiology Letters. 314 (1): 34–41. doi:10.1111/j.1574-6968.2010.02134.x. PMID 21087296.
  5. Limor, J. R.; Lal, A. A.; Xiao, L.; et al. (2002). "Detection and differentiation of Cryptosporidium parasites that are pathogenic for humans by real-time PCR". Journal of Clinical Microbiology. 40 (7): 2335–8. doi:10.1128/JCM.40.7.2335-2338.2002. PMC 120558. PMID 12089244.
  6. "CDC Cryptosporidiosis Fact Sheet". Archived from the original on 29 February 2000. Retrieved 18 April 2008.
  7. "Virginia Commonwealth University CSBC Cryptosporidium Research Website". Retrieved 18 April 2008.
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