Effect of oral chronic intoxication with sodium arsenite on murine giardiasis.
Chronic exposure to toxicants alters immune function that can affect the ability of the host to mount a response to infection. Giardiasis is a gastrointestinal disease in which subtle alteration in immunity of the host can transform the normal acute infection into a chronic one. In this work we used a murine giardiasis model to evaluate the effect of chronic oral intoxication with sodium arsenite on the characteristics of giardiasis. BALB/c mice were intoxicated during 45 days with water containing 50, 125 or 250 microg/mL sodium arsenite. Each group was then inoculated with G. muris cysts. Cysts excreted in the feces were isolated and quantified. The toxic effect of arsenic on intestinal trophozoites was evaluated using G. lamblia trophozoites cultured in vitro with different arsenic concentrations, corresponding to equivalent concentrations of arsenic found in the gut lumen of intoxicated mice. Mice intoxicated with 125 and 250 microg/mL of sodium arsenite and infected with G. muris cysts displayed a shorter period of cysts excretion and were resistant to secondary infection with the parasite. In vitro studies showed that G. lamblia trophozoites were able to grow in presence of high sodium arsenite concentrations, suggesting the absence of a direct toxic effect on the parasite in the gut. Since a longer period of Giardia cysts excretion is associated with suppression of the immune system, the earlier clearance of primary G. muris infection in intoxicated mice suggests the induction of an immune modification that leads to an improved ability of mice to overcome the infection.