Elsevier

Veterinary Parasitology

Volume 167, Issues 2–4, 10 February 2010, Pages 149-154
Veterinary Parasitology

Review
Factors contributing to emergence of Ehrlichia and Anaplasma spp. as human pathogens

https://doi.org/10.1016/j.vetpar.2009.09.016Get rights and content

Abstract

Ehrlichioses and anaplasmoses are caused by α-proteobacteria within the family of Anaplasmataceae. These diseases have been known for a long time in veterinary medicine and recently in human medicine. These tick-borne zoonoses are considered as emerging diseases. The first case of human monocytotropic ehrlichiosis occurred in 1986. Human granulocytic anaplasmosis was described as a separate entity in 1994 and ehrlichiosis caused by Ehrlichia ewingii was reported in humans in 1999. The number of cases has been rising steadily due to better diagnostic techniques and better surveillance worldwide. In this review, we will present human and animal ehrlichioses and anaplasmoses as emerging diseases and present candidate(s) for the future.

Section snippets

Human monocytotropic ehrlichiosis

In 1986, the first case of human monocytotropic ehrlichiosis (HME) was described when an astute physician saw peculiar intracytoplasmic inclusions in several monocytes in a blood smear of a severely ill man. This patient had been bitten several times by ticks in Fort Chaffee, Arkansas 2 weeks earlier. The inclusions were identified as possible clusters of bacteria belonging to the genus Ehrlichia, based on the similarity of these inclusions with E. canis, a well-known canine pathogen in the

E. ewingii: animal and human pathogen in the United States

E. ewingii was first described in 1971 in a dog in Arkansas (Ewing et al., 1971) then recognized as the agent of canine granulocytic ehrlichiosis in 1992 (Anderson et al., 1992). Canine granulocytic ehrlichiosis occurs mostly in the southcentral and southeastern United States, and its vector is the same as for E. chaffeensis (A. americanum) (Anziani et al., 1990). The main reservoir is most likely the white-tailed deer (Yabsley et al., 2002). Polymorphonuclear neutrophils are the target cells

Human anaplasmosis in the United States

The first human case of granulocytic anaplasmosis was reported in the United States in 1994 (Chen et al., 1994). Six patients with a febrile illness from Minnesota and Wisconsin had granulocytic cytoplasmic morula which suggested ehrlichiosis. Two cases had a fatal outcome. A 1.5-kb DNA product was amplified with 16S rDNA analysis from one patient. Analysis of the sequence revealed a product very similar to Ehrlichia phagocytophila (99.9%) and Ehrlichia equi (99.8%) which had never been

Is Ehrlichia canis a human pathogen?

E. canis is an intracellular bacterium with a tropism for canine monocytes and macrophages. It is transmitted by the brown dog tick, Rhipicephalus sanguineus (Lewis et al., 1977). E. canis causes canine monocytic ehrlichiosis (CME). It was first described in 1935 in Algeria (Donatien and Lestoquard, 1935) and is currently reported all around the world with high frequencies in tropical and subtropical areas (Hua et al., 2000, Suksawat et al., 2001). Previously, E. canis was not considered as a

Ehrlichia ruminantium: a human pathogen?

E. ruminantium is transmitted by tick of the genus Amblyomma and causes heartwater in ruminants in sub-Saharan Africa, Madagascar and some Caribbean Islands. No reliable vaccine is available and infected animals frequently die before treatment with tetracycline can be initiated. Serological tests for E. ruminantium lack specificity and the most reliable technique for diagnosis is PCR and probing for a section of the organism's genome. Recently, three patients were reported in South Africa, two

Other anaplasmataceae of unknown pathogenicity

In recent years, several bacteria in the family Anaplasmatacea have been detected or isolated from ticks in different countries. Two new organisms from the E. canis group were identified in ticks from Mali and Niger using polymerase chain reaction (PCR) and sequence analysis of amplified products (Parola et al., 2001). In addition, a molecular survey of Ehrlichia infection in ticks collected from animals in Japan revealed a new Ehrlichia spp. in Ixodes ovatus ticks by PCR. Subsequent sequence

Conclusion

Ehrlichioses and anaplasmoses have been known for a long time in veterinary medicine but these diseases are considered as emerging diseases in human medicine because of their relatively recent description and their steady increase in incidence in several parts of the world. Various factors have contributed to the emergence of these tick-borne illnesses, including better awareness by physicians; better diagnostic tools, including modern techniques in molecular biology; changes in the environment

Conflict of interest

None declared.

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