Heterogeneity in malaria transmission: underlying factors and implications for disease control

Abstract

In this chapter, we describe the current evidence for the existence of hotspots of malaria transmission. Heterogeneity is a common element of many infectious diseases, whereby infection and disease are concentrated in a small proportion of individuals and not distributed evenly across the population. In malaria this heterogeneity is manifested as small groups of households, or hotspots, within malaria endemic communities that are at a substantially increased risk of malaria transmission compared to surrounding households. These hotspots exist in all transmission settings, but are most easily detected at low transmission. The ecological, human and entomological factors that influence the occurrence of hotspots are currently not fully understood. Human genetic components are strongly related to the risk of (severe) clinical disease but their role in determining the location and intensity of hotspots remains uncertain. The roles of factors related to mosquito exposure are more apparent in defining geographical patterns in transmission intensity. The importance for malaria control and elimination lies in the fact that hotspots maintain transmission in low transmission seasons, representing the source of infection to the general community when vector densities increase. Hotspots of malaria transmission thereby form small geographical areas where malaria transmission is more intense and from where malaria may spread to the remainder of the community. Interventions targeted to hotspots of malaria transmission hold promise to reduce transmission intensity in the community as a whole. Before hotspots can be targeted, operationally attractive approaches to identify them need to be defined. Some of these approaches are described in this chapter together with a tool-box for hotspot-targeted interventions.