Anaplasmosis Information for Health Professionals - Minnesota Dept. of Health

Anaplasmosis Information for Health Professionals

Anaplasmosis, formerly known human granulocytic ehrlichiosis (HGE), is a bacterial disease transmitted to humans by Ixodes scapularis (blacklegged tick or deer tick), the same tick that transmits Lyme disease. The etiologic agent of anaplasmosis is Anaplasma phagocytophilum, a rickettsial bacterium.

The disease was first recognized during 1993 in several patients from Minnesota and western Wisconsin. Human ehrlichiosis, a similar disease, is caused by Ehrlichia chaffeensis and is found throughout much of southeastern and south-central United States. Human ehrlichiosis is not a common vector-borne disease in Minnesota at this time, but a small number of cases have been reported.

Another related form of ehrlichiosis caused by the Ehrlichia muris-like agent was identified in Minnesota and Wisconsin patients in 2009. Since then, low numbers of cases have been reported in both states.

On this page:
Clinical presentation
Diagnostic tests

Clinical Presentation

Onset of illness occurs 5 to 21 days after exposure to an infected tick. Common signs and symptoms include fever (often over 102°F), chills, headache, and myalgias. Nausea, vomiting, anorexia, acute weight loss, abdominal pain, cough, diarrhea, and change in mental status are reported less frequently. Highly suggestive laboratory findings include leukopenia (WBC< 4,500/mm³), thrombocytopenia (platelets <150,000/mm³), and increased aminotransferase levels. Unusual presentations may be the result of coinfections with Borrelia burgdorferi (Lyme disease agent) and/or Babesia microti (babesiosis agent), as a single feeding tick may transmit multiple disease agents.

Cases of anaplasmosis acquired through blood transfusions have been documented. Include anaplasmosis in the rule-out for patients who develop a febrile illness with thrombocytopenia following blood transfusion. Suspected transfusion-associated anaplasmosis should be reported to MDH and the supplying blood center.

Diagnostic tests

Any two of the following three tests for evidence of infection with Anaplasma phagocytophilum are recommended.

  • Polymerase chain reaction (PCR) assays are recommended, particularly for acute cases, to detect bacterial DNA and distinguish between Ehrlichia and Anaplasma species.
  • An indirect immunofluorescence assay (IFA) is the principal test use to detect anaplasmosis infection. Acute and convalescent phase serum samples can be evaluated to look for a four-fold change in antibody titer to A. phagocytophilum.
  • Intracellular inclusions (morulae) also may be visualized in granulocytes on Wright- or Giemsa- stained blood smears.


Anaplasmosis patients typically respond dramatically to doxycycline therapy (100 mg twice daily until the patient is afebrile for at least 3 days). Other tetracycline drugs also are likely to be effective. In general patients with suspect anaplasmosis and unexplained fever after a tick exposure should receive empiric doxycycline therapy while diagnostic tests are pending, particularly if they experience leukopenia and/or thrombocytopenia.



  • Reporting Anaplasmosis
    Minnesota Rules Governing Communicable Diseases require health care providers to report confirmed or suspected cases of anaplasmosis to the Minnesota Department of Health (MDH) within 1 working day.

    MDH staff also are available to provide clinical consultation regarding diagnosis and treatment of anaplasmosis and other tick-borne diseases. Call 651-201-5414 for a clinical consultation.

Updated Thursday, 14-Feb-2019 08:28:57 CST