''Ehrlichia chaffeensis'' is an obligate intracellular, Gram-negative species of Rickettsiales

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. It is a zoonotic pathogen transmitted to humans by the lone star tick (''Amblyomma americanum''). It is the causative agent of human monocytic ehrlichiosis. Human monocytic ehrlichiosis caused by ''E. chaffeensis'' is known to spread through tick infection primarily in the Southern, South-central and Mid-Atlantic regions of the United States. In recent years, the lone star tick has expanded its range along 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 Fort Chaffee Joint Maneuver Training Center, also known as Fort Chaffee, is an Arkansas Army National Guard Military base, installation located in western Arkansas, adjacent to the city of Fort Smith, Arkansas, Fort Smith. Established as Camp C ...

, where the bacterium 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 The white-tailed deer (''Odocoileus virginianus''), also known Common name, commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, North, Central America, Central and South America. It is the ...

(''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. Some evidence shows 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 uninfected 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 uninfected reservoir organisms. Transovarial transmission is not known to occur, so eggs and unfed larvae are not believed to be infected.

Pathogenesis

''E. chaffeensis'' causes human monocytic ehrlichiosis and is known to infect monocytes. It has also been known to infect other cell types such as lymphocytes, atypical lymphocytes, myelocytes, and neutrophils, but monocytes appear to best harbor the infection. ''E. chaffeensis'' has also been shown to infect canines both naturally and artificially.Baneth, G. (2010). ''Ehrlichia and anaplasma infections''. Paper presented at World small animal veterinary congress. Retrieved from http://www.ivis.org/proceedings/wsava/2010/d12.pdf Symptoms in canine infections are hard to differentiate between ''E. chaffeensis'' infection and ''E. canis'', which is the species of ''Ehrlichia'' that most commonly affects canines.

Signs and symptoms

Patients display early symptoms within 1 to 2 weeks after tick infection. Early symptoms include fever, headache, malaise, low-back pain, or gastrointestinal symptoms. Some patients may also have myalgias or arthralgias, and an estimated 10–40% of patients may develop coughing, pharyngitis, diarrhea, vomiting, abdominal pain, and changes in mental status.

Diagnosis or detection

A variety of procedures have been used to detect ''E. chaffeensis'' in humans and reservoir organisms. Most commonly, serologic testing and PCR amplification are used.

Treatment

''E. chaffeensis'' is susceptible to tetracyclines. Doxycycline treatment is suggested for any patients presenting symptoms of an ''Ehrlichia'' infection during the appropriate season and potential tick exposure.

References