Evaluating changing malaria transmission in a rural village, in coastal Tanzania, by assessment of IgG antibodies against Plasmodium falciparum and Anopheles gambiae antigens
The changing epidemiology of malaria in Sub-Saharan Africa over the last decade needs further understanding. A longitudinal project on the epidemiology of malaria was set up in the Nyamisati village, Rufiji District, Tanzania in 1985. Cross-sectional surveys have revealed a gradual decrease in parasite prevalence over the last 25 years, from >90% to 13% (by PCR), despite the absence of large scale control interventions. Although PCR provides good detection of low level parasitemia, assessment of parasite prevalence alone may not fully reflect the level of exposure in a population. In order to further understand the long-term dynamics of malaria transmission in this setting, we combined an assessment of parasite prevalence with analyses of IgG antibodies against antigens of the P. falciparum parasite and a salivary antigen of the Anopheles vector. The study included children 1–16 years old participating in cross-sectional surveys in Nyamisati village in 1995, 1999 and 2010. Parasite prevalence was established by PCR. Detection and quantification of IgG antibodies against P. falciparum crude schizont extract (PfSE) and Anopheles gambiae salivary gland protein 6 (gSG6) were performed with enzyme-linked immunosorbent assay (ELISA). Levels of IgG antibodies against merozoite surface protein 1–19 (MSP-119) and merozoite surface protein 2 (MSP-2) were assessed using a multiplexed bead-based immunoassay. Parasite prevalence and the prevalence and levels of IgG antibodies against PfSE, MSP-119 and MSP-2 decreased between 1999 and 2010, with the most marked reduction among the youngest children (1–4 years of age). The prevalence and levels of anti-gSG6 IgG antibodies showed a similar pattern. These findings suggest a substantially decreased intensity of malaria transmission in the Nyamisati area over the past 10 years, together with an evident decrease in the population level of exposure to the malaria vector
