Figure 3. An. gambiae entomological inoculation rates and infection outcomes in Africa.

(A) The clinical outcome of P. falciparum sporozoite inoculation by an An. gambiae mosquito depends on many factors and can range from no infection to severe malaria and death. Greenwood et al. (121) estimated that in areas of high transmission, for every 400 infectious bites, 200 result in a parasite infection, half of which will develop uncomplicated malaria, with two cases of severe malaria and one death. (B) Relationship between the mosquito entomological inoculation rate (EIR) and the proportion of individuals infected with P. falciparum (14). Analysis of combined data from over 90 African communities indicated that 20% of people received 80% of infections and that enormous reductions of existing EIRs would be required to achieve even a modest decrease in parasite prevalence. For example, a two-fold reduction in the EIR, from 200 to 100 infectious bites per year, would reduce parasite prevalence by only 4%, whereas a 100-fold reduction in the EIR, from 100 infectious bites to 1 infectious bite, would reduce parasite prevalence from about 70% to 30%. Part B was generated based on data from ref. 14.