Temporal study of acquired resistance in infections of mice with Giardia muris.

Swiss CD-1 mice infected with cysts of Giardia muris are protected against a challenge infection. A temporal study of this phenomenon was undertaken using two different approaches. First, the time needed for mice to acquire resistance was assessed by terminating the first infection using metronidazole on days 3, 6, 12, 24 or 48. These animals received a challenge infection 7 days later. Second, the duration of the protection was determined by giving mice a challenge infection on days 30, 60, 90, 120 or 150 after the primary infection. In all cases, a significant reduction in both cyst output and trophozoite numbers in the small intestine was observed after challenge. The reduction in cyst output following challenge was similar to the reduction in trophozoite numbers. The acquired resistance of some inbred strains of mice to G. muris was similar to that of CD-1 Swiss mice. These results show that mice can acquire a significant resistance against G. muris even after a short period of contact with the parasite (3 days) and that the resistance may last up to 21 weeks.