Immunologic response to infection with Giardia lamblia in children: effect of different clinical settings.

Infection with Giardia lamblia varies in both its severity and duration. A high incidence of giardiasis in immunoglobulin-deficient individuals suggests a role for the humoral immune response in resistance to Giardia infection. Levels of specific anti-Giardia antibodies were determined in three populations of children infected with the parasite: in children attending a day-care centre in which strict hygiene measures were practised and in whom all Giardia infections were asymptomatic; in a rural population residing under poor hygienic conditions in close proximity to farm animals in which children with Giardia-associated diarrhoeal episodes were studied; and in Bedouin infants followed from birth and in whom a previous study has shown that Giardia infection is almost universal by the age of 2 years. In day-care children, infection was accompanied by a significant increase in anti-Giardia IgM levels, compatible with an initial exposure to the parasite. In populations in which exposure to the parasite occurs at an early age and the prevalence of infestation is high, the pattern of specific antibodies to the parasite is rather uniform and cannot differentiate between current infection and previous exposure. Thus, other immune parameters such as salivary or urinary secretory IgA, which reflect the intestinal IgA response, should be studied in order to delineate further the humoral immune response to Giardia.