Middle East DVEP - Armed Forces Pest Management Board

(but not pneumonic plague) in most recipients for several months. Booster injections arenecessary every six months. Vaccination should not be relied upon as the sole preventivemeasure.M. West Nile Fever.West Nile fever is a mosquito-borne illness characterized by fever, headache, muscularpain, and rash. Occasionally, serious complications involve the liver and nervous system.The etiological agent, West Nile virus (WNV), is named after the district of Ugandawhere the virus was first isolated. It is a Flavivirus closely related to viruses causingJapanese encephalitis and St. Louis encephalitis. Infection with WNV is most oftenasymptomatic. The incubation period ranges from 1 to 6 days and clinically resembles amild dengue-like illness.Military Impact and Historical Perspective. WNV was isolated in 1937 and was oneof the earliest human arboviral infections to be documented. Undoubtedly, WNV hasbeen the cause of many cases classified as fevers of unknown origin in militarypersonnel. In view of the mild illness and the infrequent occurrence of epidemics, themilitary impact of this illness would be minor, particularly in comparison with otherdiseases in the Middle East. Infection with WNV will complicate diagnoses by medicalpersonnel, since West Nile fever cannot be clinically distinguished from many otherarboviral fevers.Disease Distribution. WNV has been isolated in many areas of Africa, Europe, Indiaand Pakistan. Viral isolations from vertebrate hosts and mosquitoes, and serologicalsurveys of humans and suspected reservoir hosts indicate WNV is widespread throughoutthe Middle East.Transmission Cycle(s). WNV has been isolated from numerous wild birds andmammals. Serological surveys have demonstrated WNV antibodies in wild and domesticbird species, wild mammals such as lemurs, rodents and bats, and domestic animals suchas camels, horses, mules, donkeys, goats, cattle, water buffalo, sheep, pigs and dogs.However, birds are considered to be the primary reservoir for WNV and may reintroducethe virus during seasonal migrations. Infections in most mammals fail to produceviremias high enough to infect potential vectors. WNV has been isolated from severalspecies of mosquitoes in nature, and they are recognized as the major vectors, especiallyCulex spp. WNV has also been recovered from bird-feeding ticks and mites. A naturalbird-tick zoonotic cycle has been suggested, but the role of ticks in the naturaltransmission of WNV has not been well defined. Mosquitoes are clearly implicated inthe transmission of WNV to humans. WNV replicates quickly in mosquitoes whentemperatures exceed 25 o C. Infected mosquitoes can transmit WNV for life.Vector Ecology Profiles.Culex univittatus is the primary vector. Anopheles coustani, Cx. antennatus, Cx. pipienspipiens, Cx. p. molestus and Cx. perexiguus are potential vectors. The tick Ornithodoroscapensis is a possible zoonotic vector of the virus in colonial birds inhabiting islands inthe Caspian Sea off the coast of Azerbaijan.102