Cryptosporidium
Cryptosporidium are protozoan that infects humans and non-human hosts. Fifteen species are infectious for non-human vertebrate host; however only seven of these (Cryptosporidium baileyi, Cryptosporidium canis, Cryptosporidium felis, Cryptosporidium hominis, Cryptosporidium meleagridis, Cryptosporidium muris and parvum) have been report to infect humans. The majority of species of Cryptosporidium appear to have some host specificity but are not strictly host specific.
Data has shown that Cryptosporidium hominis is common in humans whereas Cryptosporidium parvum is common in zoonotic species. The remaining species that have caused infections occurred mainly in patients with weak immune system.
Cryptosporidium species exists as a spherical oocyst (5um diameter) in the environment. The wall of the oocyst is made up of complex carbohydrates and lipids which surround four banana shaped sporozoites. This makes the oocyst extremely resistant to the environment.
After ingestion and exystation, the sporozoites stage enters into the host cells and begins a complex infection process. Asexual reproduction is followed by sexual reproduction where female macrogamonts and male microgamots develop and fertilisation occurs.
The resulting zygote zygote then develops a thick walled infectious oocyst that will exit the host or developed a thinned walled oocyst that will auto-infect the host.
