5 Things to Know About Ehrlichiosis and Anaplasmosis

Naomi Drexler, MPH, DrPH


June 21, 2022

Editorial Collaboration

Medscape &

Ehrlichiosis and anaplasmosis are emerging but underrecognized tickborne diseases in the United States. In the United States, three pathogens cause human ehrlichiosis: Ehrlichia chaffeensis, E ewingii, and E muris eauclairensis. Anaplasmosis is caused by infection with the bacterium Anaplasma phagocytophilum. A recent Subcommittee Report to the Tick-borne Disease Working Group recommended additional training of primary medical caregivers on ehrlichiosis and anaplasmosis.[1] Early and accurate diagnosis and treatment can prevent severe illness or death — but only if early signs are recognized. Here are five things you need to know about ehrlichiosis and anaplasmosis.

1. Ehrlichiosis and anaplasmosis cases are on the rise.

The number of reported anaplasmosis and ehrlichiosis cases is rising in the United States. In 2019, nearly 6000 cases of anaplasmosis and more than 2000 cases of ehrlichiosis were reported.[2,3] This is up from 1761 anaplasmosis cases and 740 ehrlichiosis cases in 2010. In 2019, anaplasmosis became the second most commonly reported tickborne disease in the United States, following Lyme disease. Moreover, these diseases are emerging in new areas as the geographic ranges of both blacklegged ticks (the vector of A phagocytophilum and E muris eauclairensis) and lone star ticks (the vector of E chaffeensis and E ewingii) are expanding. Providers and public health professionals need to know which diseases are common in their area so they can help protect communities:

  • E chaffeensis and E ewingii cases are most frequently reported from the southeastern and south-central United States, from the East Coast extending westward to Texas.

  • To date, E muris eauclairensis cases have been reported only from travelers to or residents of Minnesota and Wisconsin.

  • Although the blacklegged tick, the primary vector of A phagocytophilum, is widely distributed across the eastern United States, anaplasmosis is most frequently reported from the upper Midwest and northeastern United States.

2. Illness can be severe and even deadly if not treated early.

Although typically thought of as less severe than Rocky Mountain spotted fever, both ehrlichiosis and anaplasmosis can be life-threatening if not treated early. Early symptoms of both diseases are nonspecific, including fever, headache, and myalgia, sometimes accompanied by nausea, vomiting, and diarrhea. Rash is a rare sign of anaplasmosis but occurs in one third of adult and two thirds of pediatric E chaffeensis cases. Patients with ehrlichiosis and anaplasmosis often experience mild anemia, thrombocytopenia, leukopenia, and mild to moderate elevations in hepatic transaminases. If treatment is delayed, illness may become severe. Patients with severe ehrlichiosis may experience meningitis or meningoencephalitis, acute respiratory distress syndrome (ARDS), septic shock–like syndrome, hemophagocytic lymphohistiocytosis, and organ failure. Patients with severe anaplasmosis often experience ARDS, pneumonia, septic shock–like syndrome, rhabdomyolysis, and renal failure.

Delayed recognition and treatment are the most significant risk factors for severe ehrlichiosis and anaplasmosis. Severe anaplasmosis is more common among older adults, and severe ehrlichiosis is more common among older adults and children younger than 10 years. Immunosuppressed persons may also experience more severe disease. Fewer than 1% of anaplasmosis cases and 1%-3% of E chaffeensis cases result in death. To date, neither E ewingii nor E muris eauclairensis infections have been associated with reported fatalities.

3. Doxycycline is the recommended treatment for ehrlichiosis and anaplasmosis in persons of all ages.

CDC and the American Academy of Pediatrics (AAP) recommend doxycycline as the treatment of choice for ehrlichiosis and anaplasmosis in patients of all age groups. Early treatment is paramount to prevent severe disease and death.

In 1970, the US Food and Drug Administration placed a warning label on all tetracycline-class antibiotics, including doxycycline, noting an association with enamel hypoplasia and tooth discoloration when used during tooth development (last half of pregnancy up to 8 years of age). Newer evidence shows that doxycycline binds less readily to calcium, and a 2013 study by Todd and colleagues showed no evidence of tooth discoloration or enamel hypoplasia in children who had received short courses of doxycycline, even those who had received multiple courses before the age of 8 years.[4] This evidence has been used to update pediatric treatment guidelines by the AAP which approves the use of short courses (< 21 days) of doxycycline in children under 8 years.[5]

4. PCR assays are widely available and provide sensitive and specific test results when a patient is ill.

The most commonly available methods for the diagnosis of ehrlichiosis and anaplasmosis include molecular methods, such as PCR, and serologic assays. PCR of acute whole blood samples for the diagnosis of anaplasmosis and ehrlichiosis is widely available and the sensitivity is high. Samples should be collected within the first 14 days of illness or while the patient is still symptomatic. Sensitivity decreases following appropriate antibiotic treatment.

Several types of serologic tests are available, but the indirect immunofluorescence antibody (IFA) assay is the most widely used. Accurate interpretation relies on comparing the IgG-specific antibody titers from 2 samples: an acute sample, taken during the 2 weeks of illness, and a convalescent sample taken 2-4 weeks later. Samples taken within the first week of illness are often negative.

Other diagnostic methods, including immunohistochemistry and blood-smear microscopy, are less sensitive and rely on a trained microscopist to differentiate clusters of replicating cells (called morulae) from other intracellular structures.

5. Transfusion- and transplant-associated infections have been reported.

People are typically infected with Ehrlichia and Anaplasma species through the bite of infected ticks. In rare cases, the bacteria can be spread by other means, such as blood transfusion or solid organ transplant. A recent review by Mowla and colleagues has summarized the evidence around transfusion- and transplant-associated ehrlichiosis and anaplasmosis to date.[6]

Ehrlichia and Anaplasma infections have been reported from leukoreduced and non-leukoreduced red blood cells and platelets. Donor-derived Ehrlichia infections have been confirmed among kidney and liver recipients, and infections among heart and lung recipients are suspected. Anaplasma infections among kidney and pancreas recipients are also suspected.


Blood products and organs are not routinely screened for the presence of Anaplasma or Ehrlichia bacteria. Healthcare providers should be aware of the possibility of donor-derived infections. Prompt communication among organ procurement organizations, transplant or transfusion centers, and state and federal health authorities may lead to early identification of case clusters, reducing disease morbidity and mortality.


New videos and training tools on the diagnosis, treatment, and management of tickborne diseases are available on CDC's website, including a new clinical module on ehrlichiosis and anaplasmosis. The ehrlichiosis and anaplasmosis clinical module includes an applied clinical scenario and provides opportunities for continuing education credits for CME, CNE, CPE, CEU, CPH, CHES, MCHES, and AAVSB/RACE. See links below.

Clinical Module: Diagnosis and Treatment of Ehrlichiosis and Anaplasmosis

Rickettsial Disease Diagnostic Testing and Interpretation (

Rickettsial Disease Diagnostic Testing and Interpretation for Healthcare Providers

Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis — United States: A Practical Guide for Health Care and Public Health Professionals