No abstract

In a longitudinal study of a malaria-endemic village in southeastern Thailand, circumsporozoite (CS) antibody to sporozoites of Plasmodium falciparum was measured by an enzyme-linked immunosorbent assay to determine its usefulness as a seroepidemiologic marker of malaria transmission. The CS anti-(NANP)n antibody level and prevalence during a 25-month period paralleled the pattern of seasonal transmission consistent with conventional parasitologic and entomologic measurements. The prevalence and level of antibody decreased during the non-transmission wet season, and increased over a 1-2-month transition period between the end of monsoon rains and the onset of dry conditions, an interval of maximum vector activity. Antibody increased with age in the population. The prevalence of antibody to the asexual blood stage as measured by conventional indirect fluorescent antibody assay did not coincide with changes in transmission and was sustained throughout the study period. Thus, CS antibody appeared to reflect the relative population exposure to mosquito inoculation of P. falciparum sporozoites and provided a useful measure of malaria transmission dynamics.

We assessed the prophylactic efficacy of azithromycin (250 mg/day) against malaria in 276 adults in western Thailand in a randomized, double-blind, placebo-controlled trial. After antimalarial suppressive treatment, volunteers were randomized in a 2:1 ratio to either the azithromycin or placebo, respectively. Study medication was given for an average of 74 days. The azithromycin group (n = 179) had five endpoint parasitemias (1 Plasmodium vivax and 4 P. falciparum), and the placebo group (n = 97) had 28 endpoint parasitemias (21 P. vivax, 5 P. falciparum, and 2 mixed infections). Adverse events and compliance and withdrawal rates were similar in both groups. The protective efficacy (PE) of azithromycin was 98% for P. vivax (95% confidence interval [CI] = 88-100%). There were too few cases to reliably estimate the efficacy of azithromycin for P. falciparum (PE =71%, 95% C =-14-94%). We conclude that daily azithromycin was safe, well-tolerated, and had a high efficacy for the prevention of P. vivax malaria.

Antilymphocyte antibodies were found in 51 of 83 serum specimens from Thai children with dengue hemorrhagic fever (DHF). The lymphocytotoxic activity was complement dependent, and cytotoxicity was detected in the 19S immunoglobulin M-associated serum fractions at a temperature optimum of 15°C. Sera with lymphocytotoxic activity were cytotoxic to autologous as well as allogeneic lymphocytes from patients and healthy adult donors and were directed primarily against B cells, with some T cell cross-reactivity. This study suggests that infection with DHF induces predominately cold-reactive antilymphocyte antibodies in DHF patients that could potentially interact with peripheral blood cells of patients and modulate the humoral immune responses of patients during infection.

The circumsporozoite (CS) protein on the surface of sporozoites is the major target for antibody response(s) to the infective stage of the malaria parasite. Sera from malaria endemic areas contain both IgM and IgG antibodies that react with a dominant epitope in the tetrapeptide repeat region of the CS protein. In order to characterize the IgM CS antibody response in Plasmodium falciparum (PF) malaria, a prospective study was conducted in Thai Rangers. Variable IgM responses against the CS protein were detected in 81% of 47 PF-infected subjects. Similar to IgG response kinetics, IgM levels rose to a peak 6-10 days after detection of parasitemia and showed an apparent serum half-life of less than 25 days. The classic difference in isotype ratio (IgG/IgM) between primary and secondary antibody responses was observed to blood-stage, but not CS, antigens.