Ehrlichiosis Information for Health Professionals
Ehrlichiosis is a bacterial disease transmitted to humans by a variety of different organisms. Ehrlichia chaffeensis and Ehrlichia ewingii are transmitted by the lone star tick in the southeastern and southcentral United States. Ehrlichiosis due to E. chaffeensis is not a common vectorborne disease in Minnesota at this time, but a small number of cases have been reported, some of which have traveled to southern states where the disease is more common. In 2009, another related form of ehrlichiosis caused by Ehrlichia muris subspecies eauclairensis was identified in a small number of patients residing in or traveling to Minnesota and Wisconsin. The blacklegged (deer) tick is the suspected vector for this disease agent as it has been found in collected ticks in both Minnesota and Wisconsin. Since its discovery in 2009, low numbers of cases have been reported in both states.
Onset of illness typically occurs within a few weeks after exposure to an infected tick. Common signs and symptoms include fever, malaise, headache, and myalgia. Nausea, vomiting, and rash 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.
Patients with immunosuppressive conditions may be at higher risk of severe illness due to ehrlichiosis. Hospitalization may be necessary for severely ill patients. Because Ehrlichia organisms infect the white blood cells and circulate in the blood stream, these pathogens may pose a risk to be transmitted through blood transfusions. To date no cases of ehrlichiosis have been confirmed that can be attributed to this route of transmission. However, patients who develop ehrlichiosis within a month of receiving a blood transfusion or solid organ transplant should be reported to state health officials for prompt investigation.
Any two of the following three tests for evidence of infection with Ehrlichia species are recommended.
- Polymerase chain reaction (PCR) assays are recommended, particularly for acute cases, to detect bacterial DNA and distinguish between Ehrlichia and Anaplasma species.
- The most common serologic test for diagnosis of ehrlichiosis is the indirect immunofluorescence assay (IFA) using E. chaffeensis antigen, performed on paired serum samples to demonstrate a significant (four-fold) rise in antibody titers.
- The first sample should be taken as early in the disease as possible, preferably in the first week of symptoms, and the second sample should be taken 2 to 4 weeks later. Also, IgG titers are preferred over IgM titers since IgM antibodies are less specific than IgG antibodies and more likely to result in a false positive.
- Commercial serologic testing for Ehrlichia species and Anaplasma phagocytophilum may result in cross-reactivity for E. muris eauclairensis. Additional studies are needed to determine how frequently cross-reactivity occurs.
- Intracellular inclusions (morulae) also may be visualized in granulocytes on Wright- or Giemsa- stained blood smears. Sensitivity of this diagnostic method is highest during the first week of illness.
Ehrlichiosis 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 ehrlichiosis 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.
- CDC: Tickborne Diseases of the United States: A Reference Manual for Health Care Providers
CDC Handbook, designed as a way for health care providers to access information on tickborne diseases and tick identification.
- CDC: Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever, Ehrlichiosis, and Anaplasmosis - United States
Morbidity and Mortality Weekly Report: A Practical Guide for Physicians and Other Health-Care and Public Health Professionals
- IDSA: The Clinical Assessment, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis
Clinical Practice Guidelines by the Infectious Diseases Society of America.
- Reporting Ehrlichosis
Minnesota Rules Governing Communicable Diseases require ehrlichiosis (Ehrlichia spp.) to be reported to MDH within one working day.
MDH staff also are available to provide clinical consultation regarding diagnosis and treatment of ehrlichiosis and other tick-borne diseases. Call 651-201-5414 for a clinical consultation.