Ehrlichia
| Anaplasmataceae | |
|---|---|
| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Alphaproteobacteria |
| Order: | Rickettsiales |
| Family: |
Anaplasmataceae
|
| Genus: | Ehrlichia |
| Species: | Ehrlichia canis Ehrlichia chaffeensis Ehrlichia ewingii |
Ehrlichia is a genus of rickettsiales bacteria that is transmitted to vertebrates by ticks. This bacteria causes the Ehrlichiosis infection, which is considered zoonotic, because the main reservoir for the disease are animals.
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.
The genus Ehrlichia is named after a German microbiologist Paul Ehrlich.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. A new species of Ehrlichia was 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.
Ehrlichia have evolved greatly since they first emerged. The evolution in their genome has taken many different pathways, some of which have led to an increase in fitness and survival.
The Ehrlichia genome contains many different variants of genes that encode outer membrane proteins. These genes have gone through intense modification over long periods of time.Truncation is the most common modification that may result in a change in protein structure. Truncation can alter protein translation and provide antigenic variants to the organism. These truncated genes could have been the result of a fusion event of two short open reading frames or by a fission event. After the gene has been truncated and duplicated, the resulting protein's structure may be different than the original. This has a profound effect on the fitness of an organism. The survival of Ehrlichia depends greatly on the immune response of its host. With a higher range of outer-membrane proteins, the parasite can evade the immune system of the host more effectively and establish persistent infection.
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