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Ehrlichia chaffeensis is an obligate intracellular gram-negative species of rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick (''Amblyomma americanum''). It is the causative agent of human monocytic ehrlichiosis. Genetic studies support the endosymbiotic theory that a subset of these organisms evolved to live inside mammalian cells as mitochondria to provide cellular energy to the cells in return for protection and sustenance. ATP production in the rickettsia is biochemically identical to that in mammalian mitochondria. Human monocytic ehrlichiosis caused by ''E. chaffeensis'' is known to spread through tick infection primarily in the southern, southcentral and mid-Atlantic regions of the United States.〔Barker, R. W. (2000). Naturally occurring ehrlichia chaffeensis infection in coyotes from oklahoma. ‘’Emerging Infectious Diseases’’, 6(5), 477.〕 In recent years the lone star tick has expanded its range up the East Coast to New England, putting more humans at risk for tick-borne infections.〔Little, S. E. (2007, January). ''New developments in managing vector-borne diseases''. Retrieved from http://www.iknowledgenow.com/tocnavc2007smallanimal.cfm〕 It is named for Fort Chaffee where the bacteria was first discovered in blood samples of infected patients.〔 ==Transmission Cycle== ''E. chaffeensis'' is maintained in nature through a complex zoonotic relationship. The white-tailed deer (''Odocoileus virginianus'') is known to be the main competent reservoir for ''E. chaffeensis''〔 and the lone star tick (''Amblyomma americanum'') is the principal vector for human transmission.〔 There is some evidence that other organisms may serve as reservoirs for the bacteria such as domestic goats, domestic dogs, raccoons,〔 and coyotes.〔 ''E. chaffeensis'' can be transmitted to non-infected tick larvae when feeding on the blood from an infected host. The infection is then maintained and can be transmitted to a reservoir organism or humans at the nymphal stage. Adult ticks can maintain the infection or be infected from feeding on the blood of an infected reservoir organism and may also pass ''E. chaffeensis'' to humans or other non-infected reservoir organisms.〔 Transovarial transmission is not known to occur so eggs and unfed larvae are not believed to be infected.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ehrlichia chaffeensis」の詳細全文を読む スポンサード リンク
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