The availability of potential hosts as a determinant of feeding behavioursand malaria transmission by African mosquito populations

A simple model for the influence of host availability on vector bloodmeal c hoice is applied to estimate the relative availabilities of humans, cattle and other host populations to malaria vectors in African communities, using published human blood indices and ratios of cattle to humans. Cattle were bitten <0.01, 0.021 +/- 0.11,. 1.61 +/- 0.16 and 1.61 +/- 0.46 times as oft en as humans by Anopheles funestus, All. gambiae sensu stricto and An. arab iensis in Segera, Tanzania, and An. gambiae sensu lato in The Gambia, respe ctively. No significant feeding upon host species other than cattle or huma ns was detected. Even though An. gambiae s.l. in The Gambia were mostly An. gambiae s.s., they were 77 times more likely to choose cattle over humans than An. gambiae s.s. in Tanzania. The model accurately predicted cattle bl ood indices for the An. arabiensis population in Tanzania (predicted = 0.99 +/- 0.21 X observed + 0.00 +/- 0.10; r(2) = 0.66). The potential effect of increased cattle abundance upon malaria transmission intensity was simulat ed using fitted relative availability parameters and assuming vector emerge nce rate, feeding cycle length and survivorship were unaffected. The model predicted that increased cattle populations would not affect malaria transm ission in Tanzania but could drastically reduce transmission in The Gambia or where An. arabiensis is the dominant vector. We define the availability of a host as the rate at which a typical individual host-seeking vector enc ounters and feeds upon that host in a single feeding cycle. Mathematical mo dels based on this definition also represent promising tools for quantifyin g the dependence of vector longevity, feeding cycle length and dispersal up on host availability.