MALARIA TRANSMISSION IN URBAN SUB-SAHARAN AFRICA

TLDR

Rapid urbanization worldwide alters malaria epidemiology, with evidence of ongoing transmission across sub‑Saharan African cities, marked inter‑city and intra‑city variation, and potential shifts in immunity and vector ecology that may affect epidemic risk. The article synthesizes past literature to construct a conceptual framework explaining heterogeneity in urban malaria transmission. Meta‑analysis shows a weak negative correlation between mean annual entomologic inoculation rates and urbanicity, with EIRs of 7.1 in city centers, 45.8 in peri‑urban areas, and 167.7 in rural zones, and indicates that urbanization reduces transmission more strongly in low‑rainfall, seasonal regions.

Abstract

The rapid increase in the world’s urban population has major implications for the epidemiology of malaria. A review of malaria transmission in sub-Saharan African cities shows the strong likelihood of transmission occurring within these sprawling cities, whatever the size or characteristics of their bioecologic environment. A meta-analysis of results from studies of malaria transmission in sub-Saharan Africa shows a loose linear negative relationship between mean annual entomologic inoculation rates (EIR) and the level of urbanicity. Few studies have failed to find entomologic evidence of some transmission. Our results show mean annual EIRs of 7.1 in the city centers, 45.8 in periurban areas, and 167.7 in rural areas. The impact of urbanization in reducing transmission is more marked in areas where the mean rainfall is low and seasonal. Considerable variation in the level of transmission exists among cities and within different districts in the same city. This article presents evidence from past literature to build a conceptual framework to begin to explain this heterogeneity. The potential for malaria epidemics owing to decreasing levels of natural immunity may be offset by negative impacts of urbanization on the larval ecology of anopheline mosquitoes. Malaria control in urban environments may be simpler as a result of urbanization; however, much of what we know about malaria transmission in rural environments might not hold in the urban context.