ABSTRACT
E. chaffeensis. E. chaffeensis was isolated in 1991 and formally named after it caused the Šrst human infection in 1986.3,4 E. chaffeensis exhibits tropism for monocytes/macrophages and causes human monocytotropic ehrlichiosis (HME),
55.1 Introduction ..................................................................................................................................................................... 647 55.1.1 Microbiology, Genetics, and Pathobiology .......................................................................................................... 647
55.1.1.1 Taxonomy and Etiologic Agents ........................................................................................................... 647 55.1.1.2 Morphology ........................................................................................................................................... 648 55.1.1.3 Genetic and Antigenic Features ............................................................................................................ 648 55.1.1.4 Pathobiology ......................................................................................................................................... 649
55.1.2 Epidemiology, Clinical Features, and Pathogenesis ............................................................................................ 650 55.1.2.1 Epidemiology and Public Health .......................................................................................................... 650 55.1.2.2 Human Monocytotropic Ehrlichiosis .................................................................................................... 650 55.1.2.3 Human Ehrlichiosis Ewingii ................................................................................................................. 650 55.1.2.4 Clinical Features of Human Ehrlichosis ............................................................................................... 650 55.1.2.5 Pathogenesis of Human Ehrlichiosis .................................................................................................... 651
55.1.3 Diagnosis of Human Ehrlichiosis ........................................................................................................................ 652 55.1.3.1 Conventional Techniques ...................................................................................................................... 652 55.1.3.2 Molecular Techniques ........................................................................................................................... 652
55.2 Methods ........................................................................................................................................................................... 653 55.2.1 Sample Preparation .............................................................................................................................................. 653 55.2.2 Detection Procedures ........................................................................................................................................... 653
55.3 Conclusion and Future Perspectives ................................................................................................................................ 653 References ................................................................................................................................................................................. 654
a life-threatening zoonosis that is also associated with mild to severe infections in dogs.5,6 In humans, many (40%–60%) E. chaffeensis infections require hospitalization,7,8 and there is a case fatality rate of 3% due to the difŠculty in making an early and accurate diagnosis. E. chaffeensis is maintained in nature in a zoonotic cycle primarily in white-tailed deer, but dogs may also be a signiŠcant natural reservoir.9 The primary vector is the lone star tick, Amblyomma americanum, which is distributed from west central Texas throughout the southeastern, south central and mid-Atlantic states.9,10 E. chaffeensis DNA has been detected in other tick species, including Dermacentor variabilis, Ripicephalus sanguineus, Ixodes paciƒcus, I. rincinus, A. testudinarium, and Haemaphysalis yeni. Larval ticks become infected with E. chaffeensis after feeding on an infected vertebrate hosts and maintain a transstadial but not transovarial infection. The emergence of E. chaffeensis appears to coincide with changes in demographic and ecologic factors including increases in vector and mammalian host populations and human contact with natural foci, immunocompromised and aging human populations, and improved diagnosis and reporting.9 E. chaffeensis can be cultivated in vitro in various mammalian and tick cell lines11 but causes only transient subclinical infection in immunocompetent mice.12
