Anti-NANP antibody and treatment efficacy in patients with acute uncomplicated falciparum malaria attacks

African patients originating from the hypoendemic, urban area of Greater Da kar (Senegal, West Africa) who presented wit an acute Plasmodium falciparum infection were studied using an in-vivo chloroquine sensitivity assay for 28 days. Forty-seven patients with acute malaria infections were treated wi th 25 mg/body weight of chloroquine. Adequate responses to treatment were o bserved in 24 patients (51%), whereas 23 (49%) were resistant. On the day o f admission, these two groups of patients were comparable with respect to a ge, level of parasitemia and delay before initiation of treatment, but not with respect to gametocyte prevalence which was higher in patients resistan t to therapy (48%) than in those who responded to treatment (17%). In order to evaluate whether the therapeutic response was associated with any given specific immune response, antibody activities against different stages of the parasite cycle were evaluated: anti-NANP repeats (i.e. antisporozoite s tage antigen), anti-Pfs 45 kDa (i.e. antigametocyte stage antigen), and ant i-MSP3 (i.e. antimerozoite stage antigen) antibodies were measured by ELISA at day 0 (i.e. on the day of admission and before initiation of treatment) , day 7 and da 28. No significant differences between treatment-sensitive a nd treatment-resistant infections were observed for antibody prevalences an d optical densities, except at day 0, when the prevalence of antibodies aga inst NANP repeats was 2.4 times more frequent in the group of patients with a propitious response to treatment; 62.5% of the patients with an infectio n sensitive to chloroquine had anti-NANP antibodies, whereas only 26.1% of the patients resistant to chloroquine treatment had such a humoral response . These observations are discussed in relation to (1) the finding that game tocyte prevalence was markedly increased at a time when resistance to antim alarial treatment was observed; (2) the possibility that the efficacy of th e therapeutic response could be the result of the combined effects of treat ment and the individual immune status of the patients at the time of drug c ure; and (3) the presence of detectable anti-NANP activity as potential ind icator of the level of premunition acquired in an area of low seasonal mala ria transmission.