Ehrlichiosis overview
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Overview
Ehrlichiosis is a tickborne[1] bacterial infection,[2] caused by bacteria of the family Anaplasmataceae, genera Ehrlichia and Anaplasma. These obligate intracellular bacteria infect and kill the white blood cells. Ehrlichiae are transmitted to humans by the bite of an infected tick. Usually, symptoms occur within 1-2 weeks following a tick bite. [3]
Historical Perspective
Ehrlichiosis was first observed in the 19th century by the German microbiologist, Paul Ehrlich. Originally it was classified under the genus Rickettsia, however further observation led to a reclassification of the bacteria as a separate genus, Ehrlichia. The first Ehrlichia based infection was reported in South Africa in 1900. In the 1980's, Ehrlichiosis was recognized as a disease present in the United States. By 1999, Ehrlichia became a disease reportable to the Centers for Disease Control and Prevention.
Classification
Three strains of Ehrlichia (E. ewingii, E. chaffeensis, and E. Muris) are responsible for human infection. These resulting infections present themselves with very similar, if not the same, clinical manifestations. Endemic regions are different among the different diseases which may be used to diagnose the organism of infection.[4]
Pathophysiology
Differentiating Ehrlichiosis from other Diseases
Ehrlichiosis must be differentiated from other diseases that cause fever, chills, headaches, body ache, and rash. When trying to differentiate Ehrlichiosis from other infections, it is important to recognize that the clinical manifestations of Ehrlichiosis greatly resemble those of other tick-borne illnesses, especially those caused by the Rickettsiae family. Examples of misdiagnoses, with the umbrella of tick-borne diseases include typhus-spotted fevers and Colorado tick fever.
Epidemiology and Demographics
Ehrlichiosis was deemed a reportable disease by the United States Center for Disease Control and Prevention in 1999. Since the year 2000 the number of reported cases has increased from 200 (in 2000) to 961 in 2008. However it should be noted that amount of reported cases was lessened in 2010.
The majority of cases are currently reported in Oklahoma, Missouri, and Arkansas. Other endemic areas include the South central and Southeastern United States. Incidents are highest among males and adults between the ages of 60 to 64 years of age. Cases have also been reported at higher rates among individuals with compromised immune systems.
Risk Factors
The primary risk factors associated with Ehrlichiosis are exposure to endemic environment and the time of that exposure. Lone Star ticks have been identified as the primary vector of E. ewingii and E. chaffeensis infections, thus being bitten in an endemic area may result in the contraction of the disease. (The primary vector of E. muris has not yet been verified.)[4]
Natural History, Complications and Prognosis
References
- ↑ CDC "Questions and Answers" page for tickborne rickettsial diseases
- ↑ Dawson, Jacqueline E., Marty, Aileen M. (1997). "Ehrlichiosis". In Horsburgh CR, Nelson AM. Pathology of emerging Infections. 1. American Society for Microbiology.
- ↑ CDC Ehrlichiosis main information page
- ↑ 4.0 4.1 Ehrlichiosis Symptoms. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/ehrlichiosis/symptoms/index.html Accessed on December 30, 2015