Ehrlichia Infection (Ehrlichiosis)


Ehrlichiosis is a general name for a group of acute, febrile, bacterial illnesses, caused by bacteria from the Anaplasmataceae family. There are three ehrlichial species that cause disease in humans in the United States: Ehrlichia chaffeensis, Ehrlichia ewingii, and Ehrlichia muris-like (EML). The disease is transmitted to humans through bites from an infected tick. Most cases in the United States are transmitted by the lone star tick (Amblyomma americanum), which are primarily found in the southeastern and south-central United States, from the eastern seaboard to Texas. Lone star ticks are not typically found in Arizona.
Lone Star Tick

Signs & Symptoms

Most people will develop symptoms within 7-14 days after exposure to an infected tick. Early symptoms are non-specific and include:
  • Chills
  • Confusion
  • Conjunctival injection
  • Fever
  • Gastrointestinal symptoms (nausea, vomiting, diarrhea, anorexia)
  • Headache
  • Malaise
  • Muscle pain
  • Rash (in up to 60% of children, less than 30% of adults)
It is important to note that few people will develop all symptoms and the number and combination of symptoms vary greatly from person to person.


Antibodies to Ehrlichia are detectable 7-10 days after illness onset. The gold-standard serologic test looks for a four-fold change in IgG-specific antibody titers using immunofluorescence assay (IFA) on paired samples. The first sample should be taken within the first week of illness and the second should be taken 2 to 4 weeks later.
  • Demonstration of a four-fold change in IgG-specific antibody titer by immunofluorescence assay (IFA) test in paired serum samples; or
  • Detection of DNA by PCR on whole blood. This method is most sensitive within the first week of illness; may decrease in sensitivity after administration of antibiotics.
Note: IgM antibodies are less specific than IgG antibodies and are more likely to generate false positive results. IgM results alone should not be used for laboratory diagnosis.

Note: Antibody titers are frequently negative in the first 7-10 days of illness, thus serologic tests may be falsely negative during this time period. For accurate testing of suspect cases an acute and convalescent serum are necessary.

Common laboratory findings suggestive of RMSF include: thrombocytopenia (reduced platelet count), hyponatremia (reduced sodium levels), and elevated liver enzyme levels.


Use doxycycline as first-line treatment for suspected ehrlichiosis in patients of all ages. The use of doxycycline to treat suspected ehrlichiosis in children is recommended by both the CDC and the American Academy of Pediatrics Committee on Infectious Diseases. Use of antibiotics other than doxycycline increases the risk of patient death. At the recommended dose and duration needed to treat ehrlichiosis, no evidence has been shown to cause staining of permanent teeth, even when five courses are given before the age of eight.

In Maricopa County

Although Ehrlichiosis is not present in Arizona, there are still cases in residents who have traveled to an endemic area or relocated to Arizona from an endemic area. From 2005 and 2011, there were 8 probable or confirmed cases of Ehrlichiosis reported to Maricopa County.
Ehrlichiosis Case Graph
A case is a person identified as meeting the confirmed or probable case definition for a particular disease.
These classifications are for surveillance only and are not used for diagnostic purposes.

Note: These data are based on investigation data maintained by Maricopa County Department of Public Health (MCDPH) and may differ from other case counts presented in other reports by MCDPH and/or Arizona Department of Health Service (ADHS).


Reducing exposure to ticks is the best defense against Ehrlichiosis and other tick-borne infections. There are several approaches you and your family can use to prevent and control Ehrlichiosis:
  • Use insect repellants containing from 10% to 35 % DEET when camping and hiking
  • Wear light-colored long pants and long sleeved clothing so that ticks are easier to spot before they attach to the skin.
  • Remove ticks promptly, since attachment of more than 24 hours is required for disease transmission.
  • Avoid overgrown brush by walking in the center of the trail, and remove brush from personal residences.


  1. Office of Epidemiology & Data Services

    Physical Address
    4041 N Central Avenue
    Phoenix, AZ 85012

    Fax 602-372-8935