Mosquito-Borne Arboviral Surveillance and the Prediction of Disease Outbreaks

Abstract

Mosquito-borne viruses (arboviruses) have the capacity to cause widespread epidemics in humans, as well as epizootics in domestic animals and wildlife. These epidemics and epizootics can be extremely costly and disruptive. Because most mosquito-borne arboviruses can cause encephalitis and encephalomyelitis in host vertebrates, healthcare issues associated with human infections can result in significant economic impact on local economies and health care providers (Villari et al., 1995). Likewise, the loss of domestic animals to encephalitis infection can produce significant adverse financial impacts on local agricultural industries (Wilson et al., 1986; Anon, 2003). Recent mosquito-borne epidemics caused by West Nile virus (family Flaviviridae, genus Flavivirus, WNV) in North America and Chikungunya virus (family Togaviridae, genus Alphavirus, CHIKV) in the islands of the Indian Ocean are examples of how mosquito-borne viruses can severely impact local, regional, and national economies. All mosquito-borne virus disease transmission cycles are driven by four factors: 1) the annual cycle of the pathogen (the specific arbovirus), 2) the annual cycle of the mosquito vector, 3) the annual cycle of the amplification, reservoir, and secondary vertebrate hosts that are infected with a specific viral pathogen, and 4) the environmental factors that drive each biological cycle independently and at times cause these three cycles to synchronize in ways that produce epidemics and epizootics (Day, 2001). Because three biological cycles, pathogen, vector and host, inform the transmission dynamics of a specific arboviral disease, surveillance protocols have been developed to monitor each of these cycles in order to estimate the local risk of arboviral transmission for a specific region. For example, it is possible to use sentinel animals to detect and measure the spatial and temporal distributions of specific arboviruses. Sentinel chickens, pheasants, quail, pigeons, and hamsters have been successfully used to monitor the transmission of St. Louis encephalitis virus (family Flaviviridae, genus Flavivirus, SLEV), WNV, eastern equine encephalitis virus (family Togaviridae, genus Alphavirus, EEEV), and Venezuelan equine encephalitis virus (family Togaviridae, genus Alphavirus, VEEV). Likewise, competent mosquito vectors can be identified for each mosquito-borne arbovirus transmission cycle. Once regional mosquito vectors have been identified, their populations can be tracked and important factors such as abundance, population age structure, and infection status can be monitored and used to