Genetic studies of human and murine giardiasis.

Wide variation has been observed in the natural history of human and murine giardiasis, which could be due to factors associated with the parasite or with the host. In humans, prolonged infections with Giardia duodenalis have been associated with hypogammaglobulinemia, protein-calorie malnutrition, and prior gastrectomy. The duration of infection or severity of symptoms may also be influenced by the humoral immune response and by other factors such as ABO blood group and HLA antigen type. Elimination of Giardia muris is impaired in hypothymic mice, B-cell-deficient mice expressing the xid gene, and in mice deficient in mast cells. Prolonged infections also occur following depletion of helper/inducer T cells and suppression of antibody production with antisera to IgM. However, quantitative or qualitative defects in immune function do not appear to account for prolonged cyst excretion in C3H/He, C3H/HeJ, and A/J mice. The defect in these strains is influenced by several genes and may involve intermediate or late stages of macrophage activation leading to impaired elimination of the parasite.