The effect of short-term malaria chemoprophylaxis on the immune response of semi-immune adult volunteers.

In 17 semi-immune adult volunteers, chemoprophylaxis with 300 mg chloroquine base weekly for six months was found to be effective in suppressing malaria. However, following 3 months of chemoprophylaxis, a significant reduction of IFA titres was seen lasting up to 2 months after chloroquine withdrawal. There was resurgence of malaria in the post-intervention phase. 2 months after drug withdrawal, serum concentrations of IgG and factor B were significantly reduced. 3 months after initiation of chloroquine prophylaxis, a temporary but significant decrease of IgG and IgM serum concentrations was found with a corresponding decline in the number of B-lymphocytes and regulatory T-cells. These returned to normal at 6 months of chemoprophylaxis. Our findings suggest that short-term malaria chemoprophylaxis may significantly interfere with humoral and cell-mediated immunity in areas of intensive P. falciparum transmission.