Effect of two vector species on arbovirus transmission

Many mosquito-borne arboviruses have more than one competent vector. These vectors are likely to have different spatial and seasonal distributions, and interact with vertebrate hosts differently. The presence of multiple vectors for a particular virus at one location over time will influence the epidemiology of the system, and could be important in the design of intervention strategies to protect particular hosts. A simulation model of West Nile and St. Louis encephalitis viruses and Culex nigripalpus was expanded to consider two vector species. If the vectors differed only in their seasonal abundance, the presence of two vectors affected the dynamics and often resulted in multiple epidemic peaks of transmission. The abundance pattern based on Cx. nigripalpus dominated the system and was a key factor in generating epidemics in the wild bird population. The day the virus was introduced into the system was critical in determining how many epidemic peaks were observed and when the first peak occurred. Other aspects of vector competence and the differences between the two vector species also affected the likelihood of epidemics. The implications of these results for assessing the relative importance of different vector species are discussed.