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The course of Giardia lamblia infection in primary and secondary infection and early and late treated Swiss albino mice was studied. Animals treated after 3 days of infection did not show any resistance to a second challenge, whereas those treated after 9 days did show resistance to reinfection. Reinfected animals eliminated the parasites faster than the other groups. The maximum antibody levels in primary, reinfected, early and late treated groups were observed on the 20th, 10th, 20th and 15th post infection days respectively.

Activity of calmodulin and uptake of Ca2+, Na+ and Cl- was studied in control and Giardia lamblia infected mice. The activity of calmodulin was found to be significantly increased (p less than 0.001) in the experimental group as compared to control group. The uptake of Ca2+ increased significantly (p less than 0.001) while that of Na+ and Cl- decreased (p less than 0.001) in brush border membrane (BBM) vesicles from experimental group as compared to control group. In the presence of calmodulin inhibitor, trifluoperazine (TFP), the transport of Na+ and Cl- increased significantly (p less than 0.05) as compared to in the absence of inhibitor while transport of Ca2+ remained unaltered.

Direct and antibody-dependent, cell-mediated cytotoxic responses exhibited against Giardia lamblia trophozoites by peritoneal macrophages of infected animals were studied. On first exposure, the infection persisted for 30 days and peak cytotoxic responses were noticed on the 20th day post infection. In reinfected animals, peak response was on 10th day and these animals were capable of clearing the infection much faster compared with animals infected for the first time. Macrophages in Giardia infection, therefore, seem to play an important role in providing resistance to infected animals as evident from significant augmentation of their cytotoxic responses in the infected animals.

Preschool children of two villages of Kharar Taluka, Ropar district, Punjab (India) were screened for the prevalence of giardiasis. Cysts of Giardia lamblia were found in 35.1% of the stool samples and other parasites were rarely seen. The incidence of diarrhoea in association with G. lamblia positivity was 16.5% in subjects whose stool examination was positive on one or more than one occasion. No difference in the incidence of giardiasis could be seen in well nourished and undernourished children living in these endemic areas.

We measured the levels of specific secretory IgA in human milk by using an enzyme-linked immunosorbent assay. We studied Giardia lamblia-infected and -uninfected mothers to determine the role of such IgA in providing protection against Giardia infection to their children. Titers of specific secretory IgA in the milk of infected mothers were significantly higher than were those of uninfected mothers (P less than .01). Only 16% of infants of mothers with high titers of antibodies (higher OD) in their milk were infected with Giardia. In contrast, there was an infection rate of 63.0% in infants of mothers with low titers of antibody in their milk (lower OD; P less than .01).