Ehrlichiosis: Reporting and Surveillance

Ehrlichiosis is a category II reportable condition in Wisconsin. Health care providers should report to the patient's local public health department:

Reporting should be completed within 72 hours upon recognition of a case. For more information, please visit the DHS Disease Reporting page.

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 Guidance Resources

DHS surveillance resources
Provider resources

 Testing

Ehrlichia and Anaplasma infections can have similar signs and symptoms, so diagnostic tests are important to identify the specific agent causing illness. All patients who warrant testing for Ehrlichia should also be tested for Anaplasma. In Wisconsin, a panel testing for Ehrlichia and Anaplasma should be performed.

Select the tabs below to learn about different laboratory tests for ehrlichiosis.

PCR

PCR is the preferred diagnostic test because it is highly sensitive and specific during the acute disease phase (the first week of illness). PCR testing should be performed using whole blood collected upon the initial physician's visit, before starting antibiotics. A positive PCR result is serologic confirmation of Ehrlichia infection. It is important to note that a negative result does not completely rule out infection, and treatment should not be withheld due to a negative result.

Testing for E. muris eauclairensis species is only currently available commercially by PCR, and is not available by serology. Therefore, it is important for providers who routinely perform serologic testing to collect an additional sample for PCR testing of E. muris eauclairensis species if this agent is suspected.

Serologic Testing (IFA/EIA)

Serologic testing is the most common test performed in Wisconsin, even though it is less specific than the PCR test, and cross-reactivity often occurs among the Anaplasma and Ehrlichia agents. Serologic confirmation of A. phagocytophilum or E. chaffeensis infection requires evidence of a fourfold change (e.g., 1:64 to 1:256, or 1:128 to 1:512, etc.) in immunoglobulin G (IgG) specific antibody titer between paired acute and convalescent sera tested by indirect immunofluorescence assay (IFA).

  • The acute sample should be collected during the first week of illness, and the convalescent sample should be collected two to four weeks later.
  • Positive IgG titers indicate a current infection, while positive IgM titers do not.
  • IgM antibody test results are not as reliable as IgG test results, because they are less specific, and can persist for a long period of time.
  • Serologic tests based on enzyme immunoassay (EIA) only provide a positive or negative result, and cannot be used to measure changes in antibody titers between paired sera.

Cross-reactivity between A. phagocytophilum and E. chaffeensis frequently occurs with serologic testing. Therefore, the agent demonstrating a higher titer (at least fourfold higher) is the most likely agent causing illness. If there is less than a fourfold difference in titer, the agent will be undetermined.

Smear/Morulae

Labs will usually report out monocyte or granulocytes. If the smear found morulae in monocytes, the agent is most likely E. chaffeensis. If the smear found morulae in granulocytes, the agent is most likely A. phagocytophilum. E. ewingii also most commonly infects granulocytes. The target cell for E. muris eauclairensis is not known. If a laboratory routinely performs only peripheral blood smears, the Division of Public Health recommends that the blood smear testing be accompanied by a PCR or an IFA test for more definitive results.

IHC Detection/Cell Culture

These are less commonly reported positive laboratory results, but are considered confirmatory. It is very rare to see these types of test results.

 Clinically Compatible Illness

In addition to having a positive lab result, to be classified as a case of ehrlichiosis, a patient must also have clinically compatible illness. In order for an illness to be clinically compatible, the patient must exhibit:

Fever, sweats, or chills AND at least one of the following:

  • Headache
  • Myalgia (body aches)
  • Anemia (low red blood cell count)
  • Leukopenia (low white blood cell count)
  • Thrombocytopenia (low platelet count)
  • Elevated liver enzymes
  • Eschar (dark scab around the site of tick bite)
  • Rash (in up to 60% of children, less than 30% of adults)

 Treatment

Treatment for ehrlichiosis should not be delayed while awaiting further laboratory test results, or be withheld on the basis of an initial negative laboratory result, but should be started based on clinically compatible signs and symptoms and an assessment of the patient's likelihood of tick exposure. Treatment should be started immediately whenever ehrlichiosis is suspected. Delay in treatment can be extremely dangerous.


Ehrlichiosis can be treated with antibiotics. Doxycycline is the antibiotic of choice. Most people treated with oral antibiotics during the early stages of ehrlichiosis recover completely. Some patients may continue to have a headache, weakness, and malaise for weeks after adequate treatment.

The following table shows the current treatment recommendations from CDC for ehrlichiosis in adults and children.

Treatment for Ehrlichiosis
Age Category Drug Dosage Maximum Duration, Days
Adults Doxycycline 100 mg, twice per day 100 mg/dose Typically 5–7*
Children under 45 kg (100 lbs) Doxycycline 2.2 mg/kg body weight, twice per day 100 mg/dose Typically 5–7*

*Patients with suspected ehrlichiosis should be treated with doxycycline until at least three days after the fever is resolved and until evidence of clinical improvement. The minimum course of antibiotics is five days.

Antibiotic treatment following a tick bite is not recommended to prevent ehrlichiosis. There is no evidence this practice is effective, and this may only delay onset of disease.

Questions about illnesses spread by ticks? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

The recommendations in this webpage were developed in accordance with Wis. Stat. ch. 252 and Wis. Admin. Code ch. DHS 145.

Last Revised: October 27, 2021