The entomological inoculation rate and Plasmodium falciparum infection in African children

Abstract

Ronald Ross won the 1902 Nobel prize for discovering the role of the mosquito in the parasite life cycle, but his later work on mathematical models for the study of its epidemiology was perhaps even more impressive. The Ross malaria model, still referred to, assumes that humans have an equal chance of a mosquito bite, and that infection clearance is unaltered by re-infection. We now know that some people are bitten more often than others, and that repeat infections slow parasite clearance. These and other new data have been incorporated in a mathematical framework to update the Ross model for the twenty-first century. Combined with data on over 90 communities infected by malaria, this reveals that variations in biting and/or susceptibility to infection are key factors determining the prevalence of infection: 20% of people receive 80% of all infections. This finding can be used to direct malaria controls at those most likely to benefit. Malaria is an important cause of global morbidity and mortality. The fact that some people are bitten more often than others has a large effect on the relationship between risk factors and prevalence of vector-borne diseases1,2,3. Here we develop a mathematical framework that allows us to estimate the heterogeneity of infection rates from the relationship between rates of infectious bites and community prevalence. We apply this framework to a large, published data set that combines malaria measurements from more than 90 communities4. We find strong evidence that heterogeneous biting or heterogeneous susceptibility to infection are important and pervasive factors determining the prevalence of infection: 20% of people receive 80% of all infections. We also find that individual infections last about six months on average, per infectious bite, and children who clear infections are not immune to new infections. The results have important implications for public health interventions: the success of malaria control will depend heavily on whether efforts are targeted at those who are most at risk of infection.