Scientific Findings of the Southern and Central Africa International Center of Excellence for Malaria Research: Ten Years of Malaria Control Impact Assessments in Hypo-, Meso-, and Holoendemic Transmission Zones in Zambia and Zimbabwe

Abstract

For a decade, the Southern and Central Africa International Center of Excellence for Malaria Research has operated with local partners across study sites in Zambia and Zimbabwe that range from hypo- to holoendemic and vary ecologically and entomologically. The burden of malaria and the impact of control measures were assessed in longitudinal cohorts, cross-sectional surveys, passive and reactive case detection, and other observational designs that incorporated multidisciplinary scientific approaches: classical epidemiology, geospatial science, serosurveillance, parasite and mosquito genetics, and vector bionomics. Findings to date have helped elaborate the patterns and possible causes of sustained low-to-moderate transmission in southern Zambia and eastern Zimbabwe and recalcitrant high transmission and fatality in northern Zambia. Cryptic and novel mosquito vectors, asymptomatic parasite reservoirs in older children, residual parasitemia and gametocytemia after treatment, indoor residual spraying timed dyssynchronously to vector abundance, and stockouts of essential malaria commodities, all in the context of intractable rural poverty, appear to explain the persistent malaria burden despite current interventions. Ongoing studies of high-resolution transmission chains, parasite population structures, long-term malaria periodicity, and molecular entomology are further helping to lay new avenues for malaria control in southern and central Africa and similar settings.

Figure 1.

Epidemic curves of malaria in Choma District showing monthly pediatric hospital admissions for malaria and health facility malaria cases. Health facility surveillance data collection began in August 2008. The median age of children under 5 years hospitalized for severe malaria increased from 2 years in 2003 to 4 years in 2020. The proportion of health facility cases in children under 5 years decreased from 31% in 2008–2010 to 14% in 2018–2020. This figure appears in color at www.ajtmh.org.

Figure 2.

Malaria indicators in Nchelenge District showing persistently high burden despite control efforts. (Top) Parasite prevalence by rapid diagnostic test, inpatient case fatality, and timing of indoor residual spraying (IRS) campaigns, which coincides with the start of the rainy season. In 2013, an insecticide treated net distribution was done in place of IRS. (Bottom) Monthly hospital admissions for malaria and health facility cases across all age groups. Health facility cases are shown at 1/10th scale. Data begin April 2012. This figure appears in color at www.ajtmh.org.

Figure 3.

Malaria indicators in Mutasa District showing persistent seasonal malaria with sustained reductions after indoor residual spraying (IRS) with pirimiphos-methyl starting in 2014 until 2018 when the insecticide was changed to dichlorodiphenyltrichloroethane (DDT) with a subsequent rise in parasite prevalence and health center cases. (Top) Parasite prevalence by rapid diagnostic test and timing of IRS. (Bottom) Health facility malaria cases per month (bars) and cumulative cases (curves) from October to September the following year. This figure appears in color at www.ajtmh.org.