Inhibitory effect of selenium on Cryptosporidium parvum infection in vitro and in vivo.

The anticryptosporidial effect of sodium selenite (selenium) was evaluated in a bovine fallopian tube epithelial (BFrE) cell culture system and an immunosuppressed C57BL/6N adult mouse model. Parasite numbers in cell culture were significantly reduced (p<0.01) following treatment with selenium (Se) at concentrations of 6, 9, and 12 microM at 48 h postinoculation (PI) and at 1.5, 3, and 6 microM at 96 h PI. Parasite reduction was greater than 50% at 48 h PI when 9 and 12 microM Se was used, and at 96 h PI when 6 pM Se was used. Such Se-induced reduction of Cryptosporidium parvum infection was significantly (p<0.0001) blocked when using free-radical scavengers such as mannitol (20 mM). A combined solution of mannitol (20 mM) and reduced glutathione (0.5 mM) enhanced the blockage to almost 100%. Adult C57BL/6N mice were immunosuppressed with dexamethasone phosphate administered ad libitum (16 microg/mL) in drinking water and inoculated with 10(5) oocysts/ mouse. Significantly fewer (p<0.001) oocysts were shed in the feces of mice treated with Se administered ad libitum (12 microM) in drinking water than in untreated mice. The survival time of mice was also significantly increased (p<0.001) following Se treatment. Collectively, these results indicate that Se plays an important role in cryptosporidiosis, and oxidative stress caused by Se is probably a major mechanism in inhibition of C. parvum infection.