The average number of vectors directly infected by the introduction of a single infective host into a fully susceptible vector population is given by the transmission probability kx v multiplied by the initial number of mosquitoes per human N v =N h (N v~A zA e zA i is the sum of all female adult mosquitoes, regardless of the epidemic status) that survive the latent period (probability: v v =(v v zm A )), multiplied by the human infectious period 1=c: