Control of mosquito-borne diseases rests largely on avoidance of exposure, elimination of breeding sites, and destruction of mosquitoes or their larvae by methods discussed in Chapter 15. Control of alphavirus infections of humans is generally undertaken only in the face of threats of outbreaks, especially of encephalitis. Immunization of humans is currently impractical, but because encephalitis in horses is a serious disease, and because amplification in this host may increase the risk of human cases, immunization of horses each spring is an important control measure in areas subject to outbreaks. Inactivated cell culture vaccines are used for eastern, western, and Venezuelan equine encephalitides, and also an attenuated live-virus vaccine for Venezuelan equine encephalitis. Mosquito larviciding programs are carried out routinely in many areas; in short-term emergency situations, such as during an outbreak or when sentinel surveillance indicates the likelihood of an outbreak, such programs are supplemented by aerial spraying with ultra-low-volume insecticides, such as malathion or synthetic pyrethrins. Also important is public education regarding (1) source reduction, by destroying potential mosquito breeding sites, and (2) contact reduction, by avoidance of mosquito habitats, especially at dawn and dusk, and use of protective clothing, insect repellents, screening of doors and windows, bednets (particularly for infants), air-conditioning, and so on.
Currently, the only vaccines available are those described above for eastern, western, and Venezuelan equine encephalitis viruses, which are used only in horses, at-risk laboratory workers, penned pheasants, and whooping cranes! The wide prevalence of chikungunya virus in Asia and Africa, and the presence of competent Aedes aegypti and Aedes albopictus vectors in the Americas, argues for a vaccine against this agent; an experimental chikungunya vaccine is currently undergoing clinical trial in humans.
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