Ehrlichiosis is caused by obligate, intracellular bacteria. The agents causing ehrlichiosis are related to the genus Rickettsia. Ticks are the vectors. Initial symptoms are flu-like illness with leukopenia, thrombocytopenia, and elevated serum transaminases in a patient with a recent tick bite.

26,750 (US); 125,000 (Global)
Human monocytic ehrlichiosis (HME or Ehrlichia chaffeensis infection); Human granulocytic anaplasmosis (HGA or Anaplasma phagocytophilum infection); Sennetsu fever (Neorickettsia sennetsu); Neoehrlichia mikurensis infection;
7-14 days (14 days for Sennetsu fever); [CCDM]
Flu-like illness with leukopenia, thrombocytopenia, and elevated serum transaminases in a patient with a recent tick bite; [CCDM]
No evidence of person-to-person transmission other than by blood transfusion. [CCDM, p. 186]
1. Ehrlichosis is caused by obligate, intracellular bacteria living in phagosomal vacuoles and may be seen on blood smears as "morulae" in the cytoplasm of monocytes or neutrophils.
2. Human monocytic ehrlichiosis (HME) is caused by Ehrlichia chaffeensis. Human granulocytic anaplasmosis (HGA) is caused by Anaplasma phagocytophilium. Ticks are the vectors for HME and HGA. Meningoencephalitis is present in about 20% of patients. The Japanese form of ehrlichiosis (Sennetsu fever) resembles mononucleosis with sore throat, increased lymphocytes, and enlarged cervical lymph nodes. Neoehrlichia mikurensis infection has recently been described in Europe and Asia among the immunocompromised. [CCDM, p. 183-4]
3. The agents causing ehrlichiosis are related to the genus Rickettsia. HME complications include meningoencephalitis, shock, respiratory distress, and acute renal failure. In one series of cases, 26% of the patients with HME had a rash. Thrombocytopenia, leukopenia, and elevated liver transaminases are characteristic of HME and HGA infections. The case-fatality rate was 3% for HME and <0.5% for HGA. Complications for HGA include shock, seizures, pneumonitis, hemorrhage, rhabdomyolysis, and acute renal failure. Serological surveys show that organisms similar to E. chaffeensis infect humans in Europe, Africa, and Latin America. [Guerrant, p. 339-43]
4. Most HME infections are not diagnosed, but 15,527 cases were reported to the CDC between 1987 and 2017. Hospitalization is required in about 57% of cases, and at least 11% of cases are life threatening. Leukopenia is usually in the range of 1300-4000 cells/microliter, and thrombocytopenia is usually in the range of 50,000-140,000 platelets/microliter. Between 1995 and 2017, 30,759 cases of HGA were reported to the CDC. Rash is present in less than 10% of cases, but most of these are thought to be due to concurrent infection with Lyme disease (erythema migrans). Morulae can be seen in neutrophils in about 20-80% of patients. [PPID, p. 2384-8]
5. The rare human ewingii ehrlichiosis mainly infects canines, but cases in immunocompromised patients have been reported mostly in Missouri, Oklahoma, and Tennessee. [ABX Guide: Ehrlichia species]
6. The Ixodes scapularis ticks that carry Lyme disease may also carry human granulocytic anaplasmosis (HGA) and babesiosis. [IDSA Guidelines. Clinical Infectious Diseases. 2006;43:1089-1134]
7. In HME, rash may rarely affect the palms and soles. [PPID, p. 813]
8. Ehrlichiosis is in the differential diagnosis of rash and splenomegaly/hepatomegaly. [Guerrant, p. 955]
Paired sera (4-fold rise), or >1:256 IFA titer, or PCR detection; Probable case if IFA titer 1:64-128; [ABX Guide: Ehrlichia species]
HME: North & South America; HGA: North America, Europe & Asia; Sennetsu fever: Western Japan, Malaysia; Neoehrlichiosis: N. Europe & Asia; [CCDM]
  • >arthralgia
  • >fatigue, weakness
  • >fever
  • >myalgia
  • E pharyngitis
  • G abdominal pain
  • G diarrhea
  • G hepatomegaly
  • G jaundice
  • G liver function test, abnormal
  • G nausea, vomiting
  • H anemia
  • H leukopenia
  • H lymphadenopathy
  • H splenomegaly
  • H thrombocytopenia
  • N confusion, delirium
  • N headache
  • N seizure
  • N stiff neck
  • R cough
  • R dyspnea
  • S papules or plaques
  • S petechiae and ecchymoses
  • S rash (exanthem)
  • S rash on palms
  • X lung infiltrates
  • *acute renal failure
  • *ARDS
  • *bleeding tendency
  • *cranial neuropathy
  • *encephalitis
  • *meningitis
  • *myocarditis
  • *peripheral neuropathy
  • *pneumonia
  • *pneumonitis
  • *rhabdomyolysis
  • *sepsis
  • *shock
  • *stupor, coma
  • *weight loss




Needle (Includes Drug Abuse), Scalpel or Transfusion
Cattle, Goats and Sheep, Deer, Elk and Antelope, Dogs, Rodents, Human
  • Asplenic patients
  • Travel to endemic area
  • Work or play in tick-infested area
1. (US) Published in MMWR 2011 = 2675; Use correction factor of 10 for reported diseases: 2675 X 10 = 26750;
2. (Global) Guesstimate: assume 5 main areas (US, Europe, Asia, Africa & Latin America with about 25,000 cases in each area = 125,000;