Cryptosporidium hominis

Overview
Cryptosporidium hominis, along with Cryptosporidium parvum, is among the medically important Cryptosporidium species to humans. It is an obligate parasite 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.

Characteristics
C. hominis shares many similar characteristics with C. parvum including identical oocyst morphology and life-cycle. As a result, C. hominis is most easily differentiated from C. parvum through genetic analysis at specific loci.

In The Netherlands, C. hominis is responsible for an autumnal spike in cases of cryptosporidiosis, though reasons for this spike remain unclear.

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. Current avenues for treatment include scanning the Cryptosporidium hominis genome for possible targets for vaccine development.