Ehrlichiosis is a name used to describe several bacterial diseases that affect both animals and humans. They are caused by organisms in the genus Ehrlichia.

Ehrlichia chaffeensis causes human monocytic ehrlichiosis (HME). Ehrlichia ewingii can also infect humans.

Number of Ehrlichiosis cases (caused by Ehrlichia chaffeensis) reported to CDC by state health departments, 1999-2006.

Number of Ehrlichiosis cases

(Source: CDC National Electronic Telecommunications System for Surveillance (NETSS) data)

Ehrlichia HME or HGE (rickettsial diseases related to RMSF) may be fatal, however, milder and chronic forms do exist. Usually Ehrlichiosis symptoms appear within the first two weeks after exposure. Ehrlichiosis is most often transmitted by the bite of an infected tick. It is possible that individuals who become infected with Ehrlichia develop only very mild symptoms.

The number of reported cases of Ehrlichia do not reflect the true numbers.

Blood transfusions from infected individuals to uninfected individuals are a serious problem that has been responsible for a number of deaths.

IMPORTANT- Treat the patient, not the test!

Symptoms- Headaches, fever, chills, myalgias, fatigue, nausea, vomiting, and cough are some of the more prominent symptoms. It can be mistaken for the flu in milder cases. Tests can vary from lab to lab and may not detect the infection.

Treatment- Treat suspected Ehrlichia immediately. Doxycycline is the treatment of choice for adults. Doses may need to be increased or extended due to the severity or duration of the illness and co-infections involved.


J Med Entomol. 2000 May;37(3):349-56.

Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) infection in Amblyomma americanum (Acari: Ixodidae) at Aberdeen Proving Ground, Maryland.

Stromdahl EY, Randolph MP, O'Brien JJ, Gutierrez AG.

Entomological Sciences Program, U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5403, USA.


Human monocytic ehrlichiosis (HME) is a sometimes fatal, emerging tick-borne disease caused by the bacterium Ehrlichia chaffeensis. It is frequently misdiagnosed because its symptoms mimic those of the flu. Current evidence indicates that Amblyomma americanum (L.), the lone star tick, is the major vector of HME.

To determine if E. chaffeensis is present in ticks at Aberdeen Proving Ground, MD, questing A. americanum ticks were collected from 33 sites. Nucleic acid was extracted from 34 adult and 81 nymphal pools. Sequences diagnostic for E. chaffeensis from three different loci (16S rRNA, 120-kDa protein, and a variable-length polymerase chain reaction [PCR] target, or VLPT) were targeted for amplification by the PCR.

Fifty-two percent of the collection sites yielded pools infected with E. chaffeensis, confirming the presence and widespread distribution of E. chaffeensis at Aberdeen Proving Ground. Analysis with the both the 120-kDa protein primers and the VLPT primers showed that genetic variance exists. A novel combination of variance for the two loci was detected in two tick pools. The pathogenic implications of genetic variation in E. chaffeensis are as yet unknown.

PMID: 15535577 [PubMed - indexed for MEDLINE]