The Effect of Multiple Vectors on Arbovirus Transmission.

Many mosquito-borne arboviruses have more than one competent vector. These vectors may or may not overlap in space and time, and may interact differently with vertebrate hosts. 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 previously developed for West Nile and St. Louis encephalitis viruses and Culex nigripalpus was expanded to consider two vector species. These vectors differed in their abundance through the year, but were otherwise similar. The model was used to examine the consequences of different combinations of abundance patterns on the transmission dynamics of the virus. The abundance pattern based on Cx. nigripalpus dominated the system and was a key factor in generating epidemics in the wild bird population. The presence of two vectors often resulted in multiple epidemic peaks of transmission. A species which was active in the winter could enable virus persistence until another vector became active in the spring, summer, or fall. 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. The number of epidemic peaks influenced the overall proportion of birds infected. The implications of these results for assessing the relative importance of different vector species are discussed.