Chronic Trypanosoma cruzi infection associated with low incidence of 1,2-dimethylhydrazine-induced colon cancer in rats

Experimental data have demonstrated that chronic infection with intracellul ar parasites may enhance resistance against some types of tumour. This phen omenon has not yet been demonstrated for experimental Trypanosoma cruzi chr onic infection. This study investigated the effect of a specific colon canc er inducing drug, 1,2-dimethylhydrazine (DMH), on chronically T.cruzi infec ted Wistar rats. Infection was obtained by inoculation of 10(5) tripomastig ote forms by subcutaneous (s.c.) route. Acute phase of the infection was mo nitored every other day by examination of a blood smear from each animal un til negativation. In the early chronic phase of the infection, colon adenoc arcinoma was induced by weekly s.c. injections of DMH at a dose of 20 mg/kg body weight for 12 weeks. 102 animals were divided in four test groups: 39 infected rats received DMH (group 1); 32 non-infected rats received DMH (g roup 2); 16 infected rats and 15 non-infected animals were used as control groups. Animals were killed 6 months after the first dose of DMH. The whole colon was removed and prepared for light microscopic examination. Twelve a nimals from group 1 and 22 from group 2 had colon adenocarcinomas, the prop ortion of cancer being 30.7 and 68.7%, respectively (chi (2) = 10.16; P < 0 .05). The relative risk of having a colon tumor in infected animals (group 1) was 0.45 (IC 95% 0.26-0.76), which is a protective risk compared with no n-infected animals. These findings show that chronic infection with T.cruzi is associated with a lower incidence of DMH-induced colon cancer in rats.