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<br />APPEND IX B <br /> <br />Public Health and Socia-Economic Importance of Vector Problems <br />Associated with Water Resource Developments <br /> <br />Several groups of arthropods and rodents associated with the <br />development and utilization of water resources may create serious <br />public healtrr and socio-economic problems. These include species <br />that are vectors of disease organisms or serve as reservoirs of <br />~ese organisms or which otherwise interfere with man's health and <br />welfare. <br /> <br />Mosquitoes <br /> <br />Approximatel~ a dozen species of mosquitoes of public health and <br />socio-economic importance may be produced in habitats associated with <br />irrigation, impoundments, and other water resource developments. <br />Encephalitis, commonly known as sleeping sickness or brain fever, is <br />now the most important mosquito-borne disease in the United States. <br />Mosquitoes obtain the encephalitis viruses from wild vertebrates <br />and then transmit them to horses and humans. There are no effective <br />chemotherapeutic measures for preventing or treating human cases; <br />and some individuals, particularly children, who recover from <br />encephalitis often suffer permanent mental disability. Three prin- <br />cipal types of mosquito-borne encephalitis occur in the United States. <br />Eastern encephalitis (EE) occurs mainly in the Atlantic and Gulf Coast <br />States from New Hampshire to Texas, but sometimes extends as far inland <br />as Wisconsin. St. Louis encephalitis (SLE) occurs chiefly west of the <br />Mississippi River and in several of the Central States. The third type, <br />western encephalitis (WE), is confined primarily to the states west <br />of the Mississippi River. <br /> <br />Culiseta melanura and several species of Aedes mosquitoes are <br />believed to be involved in the transmission of EE. The principal <br />vector of both WE and SLE in the Far West is Culex tarsalis, a <br />mosquito which is widely distributed west of the Mississippi River. <br />In the Central States, Culex pipiens and Culex QuinQuefssciatus are <br />believed to be important in the transmission of SLE. Aedes and other <br />mosquitoes may also be involved as secondary vectors of encephalitis. <br />Both western and St. Louis encephalitis are endemic in many western <br />areas, and outbreaks of WE among horses and of WE and SLE among humans <br />have been rather widespread. In recent years, outbreaks of encephalitis <br />have occurred in irrigated areas in the Texas High Plains (l956), in <br />the Intermountain States (l957), in the Lower Rio Grande Valley (1957), <br />in Utah and New Mexico (1958), and in Wyoming (l960). <br /> <br />B-l <br />