Parasites and Oncogenesis with a Special Reference to Gastro-Intestinal Neoplasia Induced by Cryptosporidium parvum
In the last years a large number of infectious agents including virus, bacteria and parasites have been identified as direct causes or as risk factors to specific cancers around the world. Among the parasites linked to oncogenesis in humans there are strong associations. Particularly, Schistosoma haematobium is usually recognized as a cause of urinary bladder carcinoma. Some hepatic and colorectal cancers have been linked to infection by S. japonicum or S. mansoni. Moreover, a high proportion of cholangiocarcinoma in Far-East countries was imputable to Opisthorchiidae liver flukes. Among the parasitic Protists, the Apicomplexan Theileria annulata and T. parva, which are the agents of theileriosis in cows, induce often lethal lymphoproliferative process in these animals. The association between Cryptosporidium and digestive carcinomas has also been reported in a clinic study in Poland. More recently, the ability of C. parvum to induce neoplastic changes was established experimentally. This model revealed that C. parvum strains are able to induce gastrointestinal intraepithelial neoplasia in dexamethasone-treated SCID mice. Neoplastic lesions spread often to more than one digestive organ, and severity correlated with the inoculum size and the duration of the infection. Further studies are needed in order to characterize this process in mice, and to explore its occurrence in human cryptosporidiosis.
KeywordsParasites cancer oncogenesis gastro-intestinal neoplasia Cryptosporidium parvum
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