Approach Considerations
Lumbar puncture may be necessary in patients with fever and severe headache to rule out meningitis.
Buffy coat examination may reveal morulae, which are diagnostic characteristics of HME/HGA. Morulae are observed in the cytoplasm of neutrophils in patients with HGA and in monocytes in patients with HME. Only a minority of patients with HME have detectable morulae.
Lab Studies
The diagnosis of human monocytic ehrlichiosis (HME) or human granulocytic anaplasmosis (HGA) rests on (1) a single elevated immunoglobulin G (IgG) immunofluorescent antibody (IFA) Ehrlichia titer or (2) demonstration of a 4-fold or greater increase between acute and convalescent IFA Ehrlichia titers.[1]
Ehrlichiosis may also be diagnosed by demonstrating characteristic morulae in the cytoplasm of leukocytes. Morulae are diagnostic of ehrlichiosis and occur more frequently in HGA than in HME. The microbiology laboratory should be alerted to look carefully in the blood smear for them.
The infecting organism is extremely difficult to culture from blood. Detection of the organism with polymerase chain reaction (PCR) assay is possible.[11]
A complete blood cell (CBC) count should be obtained for possible neutropenia, relative lymphopenia, and/or thrombocytopenia. Anemia is not a feature of ehrlichiosis and, if present, is not a hemolytic anemia, as in babesiosis.
Atypical lymphocytes have been reported in patients with ehrlichiosis. The erythrocyte sedimentation rate (ESR) is minimally/moderately elevated in ehrlichiosis.
Elevated C-reactive protein (CRP) levels are common in the first week of illness and typically resolve by the end of the second week.
Serum transaminases should be evaluated, because they are frequently mildly elevated in ehrlichiosis, as well as in other tick-borne infectious diseases. Abnormal liver enzymes are found in 86% of patients.
DIC may be diagnosed in patients with a cutaneous bleeding diathesis who have thrombocytopenia and in whom schistocytes are observed in the peripheral smear.
If other infectious diseases are suspected, appropriate tests should be obtained to rule out these diagnoses. If coinfection with RMSF or babesiosis is suspected, appropriate serology should be obtained to diagnose each of these infectious diseases.
Microscopic examination (by an experienced microbiologist) of blood smears stained with eosin-azure type dyes, such as Wright-Giemsa stain, may reveal morulae in the cytoplasm of leukocytes. As many as 20% of patients with HME and 20-80% of patients with HGA may demonstrate this in the first week of infection. A negative result should not be taken as proof of noninfection.
Hyponatremia (< 130 mEq/L) is found in 40% of patients.
CDC. Ehrlichiosis. Accessed May 16 2011. Available at http://www.cdc.gov/ehrlichiosis.
Chapman AS, Bakken JS, Folk SM, et al. Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever, ehrlichioses, and anaplasmosis--United States: a practical guide for physicians and other health-care and public health professionals. MMWR Recomm Rep. Mar 31 2006;55:1-27. [Medline].
Buller RS, Arens M, Hmiel SP, et al. Ehrlichia ewingii, a newly recognized agent of human ehrlichiosis. N Engl J Med. Jul 15 1999;341(3):148-55. [Medline].
Aguero-Rosenfeld ME, Horowitz HW, Wormser GP, et al. Human granulocytic ehrlichiosis: a case series from a medical center in New York State. Ann Intern Med. Dec 1 1996;125(11):904-8. [Medline].
Bakken JS, Dumler JS, Chen SM, et al. Human granulocytic ehrlichiosis in the upper Midwest United States. A new species emerging?. JAMA. Jul 20 1994;272(3):212-8. [Medline].
Heilpern KL. Update: human ehrlichiosis--Maryland and Wisconsin, 1994. Ann Emerg Med. Jul 1998;32(1):108-10. [Medline].
Lovrich SD, Jobe DA, Kowalski TJ, Policepatil SM, Callister SM. Expansion of the midwestern focus for human granulocytic anaplasmosis into the region surrounding la crosse, wisconsin. J Clin Microbiol. Nov 2011;49(11):3855-9. [Medline].
Pritt BS, Sloan LM, Johnson DK, Munderloh UG, Paskewitz SM, McElroy KM, et al. Emergence of a new pathogenic Ehrlichia species, Wisconsin and Minnesota, 2009. N Engl J Med. Aug 4 2011;365(5):422-9. [Medline].
Strle F. Human granulocytic ehrlichiosis in Europe. Int J Med Microbiol. Apr 2004;293 Suppl 37:27-35. [Medline].
Hamburg BJ, Storch GA, Micek ST, Kollef MH. The importance of early treatment with doxycycline in human ehrlichiosis. Medicine (Baltimore). Mar 2008;87(2):53-60. [Medline].
Everett ED, Evans KA, Henry RB, McDonald G. Human ehrlichiosis in adults after tick exposure. Diagnosis using polymerase chain reaction. Ann Intern Med. May 1 1994;120(9):730-5. [Medline].
| Human monocytic ehrlichiosis (HME) | Human granulocytic anaplasmosis (HGA) | |
| Cell type Affected | Monocytes | Granulocytes |
| Organism | E chaffeensis | A phagocytophilum |
| Vector | Amblyomma americanum (Lone Star tick) | Ixodes scapularis (black-legged tick), Ixodes pacificus (Western black-legged tick) in California, Ixodes ricinus in Europe, and probably Ixodes persulcatus in parts of Asia |
| Location | Southeastern and south-central United States | Wisconsin and Minnesota, less active in New York and Connecticut, also California |
| Rash | 30% of adults, 60% of children | Rare |
| Prognosis | ~3% mortality | < 1% mortality |
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