Improving malaria control in West Africa: Interruption of transmission as a paradigm shift

With the paradigm shift from the reduction of morbidity and mortality to the interruption of transmission, the focus of malaria control broadens from symptomatic infections in children ≤5 years of age to include asymptomatic infections in older children and adults. In addition, as control efforts intensify and the number of interventions increases, there will be decreases in prevalence, incidence and transmission with additional decreases in morbidity and mortality. Expected secondary consequences of these changes include upward shifts in the peak ages for infection (parasitemia) and disease, increases in the ages for acquisition of antiparasite humoral and cellular immune responses and increases in false-negative blood smears and rapid diagnostic tests. Strategies to monitor these changes must include: (1) studies of the entire population (that are not restricted to children ≤5 or ≤10 years of age), (2) study sites in both cities and rural areas (because of increasing urbanization across sub-Saharan Africa) and (3) innovative strategies for surveillance as the prevalence of infection decreases and the frequency of false-negative smears and rapid diagnostic tests increases.

Graphical abstractMolecular methods such as real-time PCR provide evidence for simultaneous infection with multiple Plasmodium falciparum parasites in areas with intense transmission such as Mali. Using primers specific for the K1, MAD20 and RO33 allotypes of Block 2 in msp1 (Panel a), the studies shown here demonstrate simultaneous infection in one individual with three K1, one MAD20 and two RO33 parasite genotypes (Panels b–d, respectively). Reproduced with permission from Colborn et al. (2005).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Focusing on the interruption of transmission changes the target population from children ≤5 years of age to include older children and adults. ► Improved malaria control results in fewer parasite genotypes and lower parasite counts which increase the frequency of false-negative smears and rapid diagnostic tests. ► Other consequences of improved control include an upward shift in peak ages for infection and delayed acquisition of antiparasite immune responses.