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Ehrlichia is a genus of rickettsiales bacteria. They are transmitted by ticks. Several species can cause infection (Ehrlichiosis) in humans. The genus is named after German microbiologist Paul Ehrlich. These diseases are considered zoonotic as the main reservoir for the pathogen is in animal, usually mammal species.
Ehrlichia are obligately intracellular pathogens and are transported between cells through the host cell filopodia during initial stages of infection, whereas, in the final stages of infection the pathogen ruptures the host cell membrane.
A new species of Ehrlichia has been discovered inside the deer tick Ixodes scapularis. This newly found organism has only been isolated from deer ticks in Wisconsin and Minnesota in the USA. The species is known as Ehrlichia Wisconsin HM543746.
The first ehrlichial disease was first recognized in South Africa during the 19th century. Its tick-borne nature was determined in 1900. The organism itself was demonstrated 1925 when it was recognized to be a rickettsia. It was initially named Rickettsia ruminantium, and is currently named Ehrlichia ruminantium. In 1945 a "infection and treatment" method for livestock was developed. This is still the only commercially available "vaccine" against the disease, which is not a true vaccine, but intentional exposure to the disease with monitoring and antibiotic treatment if needed. In 1985 the organism was first propagated reliably in tissue culture.
Ehrlichia have evolved greatly since they first emerged on Earth. They have shown evidence of active genomic modifications, such as high substituiton rates, truncated genes, independent long-period tandem repeats, and pseudogenes. The most pronounced evidence of evolution in Erhlichia is the presence of the tandem repeats. These repeats vary highly among individuals and species. Over time, individuals may expand or contract parts of their genes and alleles which adds genetic variation and may sometimes affect phenotype. 
- Cowdria ruminantium (Ehrlichia ruminantium)
- Ehrlichiosis (canine)
- Human granulocytic ehrlichiosis (now called Human granulocytic anaplasmosis)
- Human monocytic ehrlichiosis
- Garrity, George (2005). Bergey's Manual of Systematic Bacteriology. Springer. ISBN 0-387-24145-0.
- Thomas S, Popov VL, Walker DH (2010) Exit Mechanisms of the Intracellular Bacterium Ehrlichia. PLoS ONE 5(12): e15775. http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0015775
- Frutos, Roger. 2007. Ehrlichia ruminantium: genomic and evolutionary features. Trends in Parasitology. 23: 414-419. http://hy2ju6vj2n.scholar.serialssolutions.com/?sid=google&auinit=R&aulast=Frutos&atitle=Ehrlichia+ruminantium:+genomic+and+evolutionary+features&id=doi:10.1016/j.pt.2007.07.007&title=Trends+in+parasitology&volume=23&issue=9&date=2007&spage=414&issn=1471-4922
- Ehrlichia genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID
- Ehrlichia at the US National Library of Medicine Medical Subject Headings (MeSH)
- Forum discution and clinical presentation (RO) Clinical experiences about ehrlichia and coinfections at dogs in Romania
-  Newly discovered species of Ehrlichia found in deer ticks
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