A study of Giardia infection in irradiated and thymectomized mice

Thymectomized and irradiated mice were infected with Giardia cysts obtained from a human source. The animals were killed on the third, sixth, ninth, 12th and 15th days post-infection. The intestinal contents were collected and a count of motile trophozoites was made. The results were compared with an infected control group of animals which were similar to the experimental group in age, sex, weight and species. There was a considerable increase in the trophozoites counts in the experimental group on the third, sixth, ninth and 12th days of the experiment with the differences from the control group being highly significant (P less than 0.001) on each comparable day of study. However, no such difference was observed on the 15th day post-infection. Both groups of animals showed an initial rise in the trophozoite counts with the peak on the 9th day post-infection followed by a fall in the counts on the 12th and 15th day. The difference on each successive day of experiment was highly significant. Six out of 30 (20%) mice in the experimental group died, with all the deaths occurring within the first 6 days post-infection. On the other hand, there were no deaths in the control group and in the uninfected thymectomized and irradiated group. These observations were further substantiated by the more severe histological changes in the villi and lymphocyte infiltration in the experimental group than in the control group. Therefore it is surmised that the intensity of Giardia infection in mice with depressed cell mediated immunity is considerably increased. However, it is interesting to note that these animals show a definite trend towards recovery as do normal animals with Giardia infection.