MURINE INFECTION MODEL FOR MAINTENANCE AND AMPLIFICATION OF CRYPTOSPORIDIUM-PARVUM OOCYSTS

Propagation of Cryptosporidium parvum is problematic because in vitro development of the parasite is poor and animals are only briefly susce ptible as neonates. At present oocysts of the parasite are usually pro cured by passage in neonatal sheep or cattle. In the present study, la rge numbers of oocysts of C. parvum could be isolated following infect ion of dexamethasone-treated adult C57BL/6 mice. The amount of immunos uppressive drug and the regimen of administration were critical for su ccessful maintenance of the parasite, however. Routinely, 10 mice (age , 8 to 12 weeks) were injected four times on alternate days with 1.0 m g of dexamethasone, and the last injection was given on the same day a s oral inoculation with 10(6) oocysts. By using a simplified procedure for oocyst purification from mouse feces, approximately 10(9) oocysts were obtained. This model is inexpensive and comparatively safe to ha ndle, and the numbers of animals inoculated can be varied to obtain th e required number of oocysts. Thus, this murine infection model would be a suitable alternative to the use of neonatal calves or sheep for e fficient oocyst propagation.