PARASITE INFECTION AND CANCER - WITH SPECIAL EMPHASIS ON SCHISTOSOMA-JAPONICUM INFECTIONS (TREMATODA) - A REVIEW

This article contains a review of current knowledge on the association of parasite infections and cancer formation, especially that of Schis tosoma japonicum (Trematoda) in man and experimental animals. The asso ciation of S. haematobium infection and bladder cancer is well known a nd documented. However, S. japonicum infection has also been reported to be associated with cancer, in this case hepatocellular carcinoma an d/or colorectal cancer. Pathological records and analyses have shown a correlation between this infection and cancer, and pathohistological descriptions have been numerous, together with clinical case reports. Epidemiological analyses have been conducted in China and Japan and su pport a role of S. japonicum infection as one of the risk factors in c ancer formation, along with others, such as hepatitis virus infection and alcoholic intake. Experimental results have also shown that cancer appears early and in larger numbers in experimentally infected animal s given a known carcinogen. In spite of these positive end-point assoc iations, the mechanism of schistosome-mediated enhancement of carcinog enesis is obscure. A suggestive observation is that in S. japonicum-in fected mice carcinogen-metabolizing hepatic activity including P-450 w as decreased so that an administered carcinogen persisted for a longer period than in uninfected mice. Further studies, both epidemiological and experimental, are needed to firmly establish the relationship bet ween schisotosome infection and cancer.