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171 - Ehrlichiosis and anaplasmosis
- from Part XXI - Specific organisms: Rickettsia, Ehrlichia, and Anaplasma
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- By Johan S. Bakken, St. Luke’s Hospital, J. Stephen Dumler, University of Maryland School of Medicine
- Edited by David Schlossberg, Temple University, Philadelphia
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- Book:
- Clinical Infectious Disease
- Published online:
- 05 April 2015
- Print publication:
- 23 April 2015, pp 1098-1102
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Summary
Ehrlichiosis is the collective name for infections caused by obligate intracellular gram-negative bacteria in the genera Ehrlichia, Anaplasma, and Neoehrlichia, family Anaplasmataceae. Members of these genera cycle between invertebrate (arthropod) and vertebrate hosts, and some cause human zoonoses. At least seven species cause human tick-borne infection in the United States and Europe, including Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis (HME), Ehrlichia ewingii, the agent of human ewingii ehrlichiosis (HEE), Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis (HGA), an Ehrlichia muris-like agent (EMLA), the Panola Mountain ehrlichia, an agent phylogenetically similar to Ehrlichia ruminantium that has caused fever in humans in the United States, Ehrlichia canis, thought limited to canids but identified as an agent of human febrile illness in Venezuela, and Candidatus Neoehrlichia mikurensis, which has caused severe sepsis-like conditions in Europe, but mild febrile disease in Asia. While human infection by Neorickettsia sennetsu periodically surfaces in Asia, the transmission and disease processes are distinct and it will not be considered here.
Most Anaplasmataceae reside in ixodid (hard-body) ticks, and the bacteria are acquired during the larval stage and passed transstadially with each successive tick stage. Amblyomma americanum (the Lone Star tick) is the vector for E. chaffeensis and E. ewingii, and its range is throughout the south and eastern United States from Maine to Texas. In addition, all documented reports of human infections are limited to North America, although some evidence suggests that they exist in ticks in South America and Asia. In contrast, A. phagocytophilum and the E. muris-like agent cycle within Ixodes species ticks. Ixodes scapularis (the black-legged or deer tick) is found in the eastern United States and is a vector for both species. In addition, Ixodes pacificus (the western black-legged tick), found in regions of the US Pacific coast (northern California, Oregon, and Washington), and Ixodes ricinus and Ixodes persulcatus, found in Europe and Asia, respectively, are competent vectors for A. phagocytophilum. Ixodes species ticks are also vectors for Borrelia burgdorferi (the agent of Lyme borreliosis), and most cases of HGA are reported from areas where Lyme borreliosis is endemic.
169 - Ehrlichiosis and Anaplasmosis
- from Part XXI - Specific Organisms – Rickettsia, Ehrlichia, and Anaplasma
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- By Johan S. Bakken, St. Luke's Infectious Disease Associates, J. Stephen Dumler, The Johns Hopkins School of Medicine
- Edited by David Schlossberg
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- Book:
- Clinical Infectious Disease
- Published online:
- 05 March 2013
- Print publication:
- 12 May 2008, pp 1173-1176
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- Chapter
- Export citation
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Summary
Ehrlichiosis is the collective name for infections caused by obligate intracellular gram-negative bacteria in the genera Ehrlichia and Anaplasma that belong to the family Anaplasmataceae. Members of these two genera cycle in nature between invertebrate (arthropod) and vertebrate (mammalian) hosts, and some species occasionally cause zoonotic infections in humans. Three species are currently known to cause human tick-borne infection in the United States and Europe and include Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis (HME), Ehrlichia ewingii, the agent of human ewingii ehrlichiosis (HEE), and Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis (HGA).
In nature Ehrlichia and Anaplasma species reside in specific hard-body tick hosts, and the bacteria are passaged transstadially with each successive developmental tick stage. Amblyomma americanum (the Lone Star tick) is the tick vector for E. chaffeensis and E. ewingii, and the endemic range of the Lone Star tick is predominately in the south and southeastern United States from Maryland to Texas. In addition, all documented reports of human infections with these species have been limited to the North American continent. In contrast, A. phagocytophilum cycles within Ixodes species ticks, including Ixodes scapularis (the deer tick) in the eastern United States, Ixodes pacificus (the black-legged tick) in some regions of the U.S. Pacific coast (northern California, Oregon, and Washington), and Ixodes ricinus (the wood tick) and Ixodes persulcatus in Europe and Asia. Ixodes species ticks are also vectors for Borrelia burgdorferi (the agent of Lyme borreliosis), and most cases of HGA have been reported from the same areas where Lyme borreliosis occurs endemically.
Lyme borreliosis (Lyme disease): molecular and cellular pathobiology and prospects for prevention, diagnosis and treatment
- Paul G. Auwaerter, John Aucott, J. Stephen Dumler
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- Journal:
- Expert Reviews in Molecular Medicine / Volume 6 / Issue 2 / 19 January 2004
- Published online by Cambridge University Press:
- 11 March 2004, pp. 1-22
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- Article
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Lyme borreliosis is a systemic infection caused by the spirochaete Borrelia burgdorferi, which is transmitted by tick bites and maintained in a delicately balanced ecological cycle. Recent increases in the population densities of tick hosts, the abundance of ticks and the proximity of man to natural tick habitats have led to an escalating worldwide incidence of Lyme borreliosis, and nonspecific clinical manifestations have yielded significant misunderstanding of the disease. After entry, B. burgdorferi activates local inflammation, yet evades host defences and facilitates dissemination by potentially masquerading with host components such as plasmin and complement. The extent of tissue injury is determined by the aggressiveness of host inflammation and immunological reactions, as well as by genetic attributes of the spirochaete. The clinical presentation can be highly varied, including early manifestations that are limited to erythema migrans and ranging to disseminated infection with arthritis, carditis, cranial nerve palsy, peripheral neuropathy, meningitis, or other manifestations. Diagnostic tests have improved, but are unhelpful during certain stages of infection. Therapy varies depending on the degree of involvement, and recovery is usually rapid and complete. Post-treatment clinical manifestations in the absence of evidence for active infection are still poorly understood. The understanding of how B. burgdorferi survives in the environment and interacts with human and mammalian hosts has improved. However, further advances in prevention and therapy depend on continued investigation of the ecological risks and improved understanding of the pathobiology of this obligate bacterial parasite.