Human Anaplasmosis Information for Health Professionals
Human anaplasmosis (HA), 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 HA 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.
Human anaplasmosis / ehrlichiosis
These disease names are often used interchangeably, which is incorrect. Human anaplasmosis (formerly “human granulocytic ehrlichiosis”; etiologic agent Anaplasma phagocytophilum) is endemic to Minnesota and is carried by Ixodes scapularis ticks (Lyme disease vector). In contrast, human ehrlichiosis caused by Ehrlichia chaffeensis is endemic to many southern states and carried by Lone Star ticks. However, another newly-identified form of ehrlichiosis is caused by the Ehrlichia muris-like agent, which is transmitted by I. scapularis ticks.
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 HA acquired through blood transfusions have been documented. Include HA 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.
Any two of the following three tests for evidence of infection with Anaplasma phagocytophilum are recommended.
- An indirect immunofluorescence assay (IFA) is the principal test used to detect HA 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.
- Polymerase chain reaction (PCR) assays are being used increasingly to detect A. phagocytophilum DNA.
HA 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 HA 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.
- Tickborne Diseases of the United States: A Reference Manual for Health Care Providers (PDF: 5,828 KB/21 pages)
CDC Handbook. Attention: Non-MDH link.
- Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever, Ehrlichiosis, and Anaplasmosis - United States
CDC: Morbidity and Mortality Weekly Report: A Practical Guide for Physicians and Other Health-Care and Public Health Professionals Attention: Non-MDH link
- The Clinical Assessment, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis
Clinical Practice Guidelines by the Infectious Diseases Society of America. Attention: Non-MDH link
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 human anaplasmosis (HA) and other tick-borne diseases. Call 651-201-5414 for a clinical consultation.