WildLife Group of the SAVA
Cryptosporidiosis in Wildlife
Dr Rick Last Specialist Veterinary Pathologist
Introduction
Cryptosporidia are small ( 2-6 um ), Apicomplexan protozoan parasites found on the surface of gastrointestinal and respiratory tract epithelium in mammals , birds , reptiles and fish . In African wildlife cryptosporidia have been identified in various antelope species , Buffalo and African elephant . Explosive outbreaks of clinical disease have been observed in antelope calves ( sable , roan ) in captive breeding facilities . Cryptosporidium parvum , Cryptosporidium ubiquitim and Cryptosporidium bovis have been identified . There are numerous reports in captive reptiles . Cryptosporidiosis is a disease of intensification and therefore more commonly observed in captive / farmed species .
Life Cycle and Pathogenesis
Cryptosporidium are coccidian waterborne protozoal parasites transmitted by environmentally hardy , thickwalled oocysts shed in the feces and transmission occurring by ingestion of these thick-walled oocysts in fecal contaminated food or water . After ingestion of the thick-walled cysts there is excystation with release of sporozoites which infect the intestinal epithelial tissue becoming trophozoites . Asexual reproduction of trophozoites ( schizogony ) produces meronts with merozoites . Some of the merozoites released can cause autoinfection by reattaching to the epithelial cells . Others develop into gamonts with sexual reproduction producing zygotes and eventually oocysts . 2 forms of oocysts are produced namely thin-walled oocysts which can rupture within the intestinal tract with release of sporozoites resulting in reinfection . Thickwalled oocysts are excreted into the environment . These oocysts are fully mature and infective on excretion .
The minimum infective dose is small relative to that of other enteric pathogens , while oocyst production during the infective stage is high , resulting in heavy environmental contamination and explosive clinical outbreaks . Some oocysts produced are thin walled and sporulate continuing the infection in the same individual ( auto-infection ), resulting in frequent relapses and debilitating infection . Other thick-walled cysts are excreted in feces . Excreted oocysts are fully sporulated and immediately infective , in stark contrast to coccidiosis where sporulation occurs in the environment .
Gastrointestinal cryptosporidiosis usually presents in 1 of 4 forms namely asymptomatic infection , acute infection ( less than 2 weeks duration ), recurrent acute infections in which symptoms reappear following a brief period of recovery for up to 30 days and a chronic infection ( more than 2 weeks ) in which symptoms are persistent . Dissemination to other organ systems is less common but may include the hepatobiliary system , pancreas , upper gastrointestinal tract , urinary bladder , respiratory system and kidney .
Infection is associated with gastrointestinal tract disease and diarrhea due to the severe villous atrophy induced by this parasite . Organisms typically are most heavily distributed in the distal half of the small intestine , especially in ileum , although occasionally cryptosporidium may occur in the cecum and colon . Neonatal animals (< 4 weeks of
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