Anaplasma phagocytophilum, Coltivirus (Colorado Tick Fever), and Ehrlichia Species

  • Diagnosis
  • Algorithms
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Influenza-like illness after exposure to tick

Laboratory Testing

  • For laboratory testing suggestions, refer to the CDC's publication, Tickborne Diseases of the U.S.
  • Clinical laboratory testing offers little help in initial diagnosis when immediate therapeutic decisions are required
  • Initial testing
    • CBC with differential
      • Thrombocytopenia and leukopenia – suggest Anaplasma phagocytophilum infection (anaplasmosis), but consider Babesia microti and coltivirus (Colorado tick fever) testing, depending on exposure region
      • Peripheral smear (Wright or Giemsa stain)
        • Morulae presence (limited sensitivity for diagnosis)
          • In granulocytes – Anaplasma infection is more common, but Ehrlichia ewingii also infects granulocytes
          • In monocytes – E. chaffeensis most common
          • Peripheral smear most useful for Anaplasma because many patients can be positive; ≤10% for Ehrlichia spp
    • Liver function tests
      • Mild elevation is suggestive for Anaplasma or Ehrlichia spp, but normal results cannot rule out either
  • If rash is present in patient in endemic region, suggest co-testing for AnaplasmaEhrlichia spp, and Borrelia spp (see Tickborne Disease Testing algorithm)
  • PCR – most sensitive method to confirm Ehrlichia spp and Anaplasma infection (particularly during early phase of disease)
    • Preferred test option for
      • Timely and accurate diagnosis
      • Rapid turn-around time
  • Antibody testing (IFA)
    • Single acute phase testing usually inadequate (most testing in first week is negative)
    • Repeat IFA serologies in 10-14 days may be helpful  
      • Seroconversion is typically best demonstrated by testing of specimens spaced 3-6 weeks apart
    • Antibodies to Ehrlichia spp and Anaplasma are highly cross-reactive (limited specificity for diagnosis)
      • Both organisms should be tested for in all suspected cases
    • Patients treated with tetracycline-class antibiotics early in infection may not seroconvert
  • Culture
    • Difficult to perform
    • May require several weeks to isolate

Differential Diagnosis

Tickborne diseases in the U.S. include

  • Anaplasmosis (or human granulocytic anaplasmosis) (Anaplasma phagocytophilum)
  • Babesiosis (Babesia microti)
  • Colorado tick fever (coltivirus)
  • Ehrlichioses (or human monocytic ehrlichiosis) (Ehrlichia chaffeensis, E. ewingii, and E. muris-like [EML])
  • Lyme disease (Borrelia burgdorferi)
  • Rocky Mountain spotted fever (Rickettsia rickettsii)
  • Spotted fever rickettsioses (Rickettsii parkeri and Rickettsii species 364D)
  • Tickborne relapsing fever
  • Tularemia (Francisella tularensis)
  • Powassan virus (deer tick virus)

Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Tick-Borne Disease Panel by PCR, Blood 2008670
Method: Qualitative Polymerase Chain Reaction

Ehrlichia and Anaplasma Species by Real-Time PCR 2007862
Method: Qualitative Polymerase Chain Reaction


Rare E. ewingii and E. canis infections cannot be differentiated by this test

Babesia Species by PCR 2008665
Method: Qualitative Polymerase Chain Reaction

Ehrlichia chaffeensis Antibodies, IgG & IgM by IFA 0051002
Method: Semi-Quantitative Indirect Fluorescent Antibody

Follow Up

May require acute and convalescent specimens to determine presence of disease

Anaplasma phagocytophilum (HGA) Antibodies, IgG and IgM 0097303
Method: Semi-Quantitative Indirect Fluorescent Antibody

Follow Up

May require acute and convalescent samples to determine presence of disease

Babesia microti Antibodies, IgG and IgM by IFA 0093048
Method: Semi-Quantitative Indirect Fluorescent Antibody


Will not detect B. duncani or strain MO-1

Follow Up

May require acute and convalescent specimens to determine presence of disease

Related Tests


Holly M. Biggs, Behravesh CBarton, Bradley KK., et al. Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever and Other Spotted Fever Group Rickettsioses, Ehrlichioses, and Anaplasmosis. 65(2);1–44. Centers for Disease Control and Prevention. Atlanta, GA [Last Updated May 2016; Accessed: May 2016]

General References

Bakken JS, Dumler S. Human granulocytic anaplasmosis. Infect Dis Clin North Am. 2008; 22(3): 433-48, viii. PubMed

Bakken JS, Dumler S. Human granulocytic anaplasmosis. Infect Dis Clin North Am. 2015; 29(2): 341-55. PubMed

Dana AN. Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations. Dermatol Ther. 2009; 22(4): 293-326. PubMed

Dumler S, Madigan JE, Pusterla N, Bakken JS. Ehrlichioses in humans: epidemiology, clinical presentation, diagnosis, and treatment. Clin Infect Dis. 2007; 45 Suppl 1: S45-51. PubMed

Harris RM, Couturier BA, Sample SC, Coulter KS, Casey KK, Schlaberg R. Expanded Geographic Distribution and Clinical Characteristics of Ehrlichia ewingii Infections, United States Emerg Infect Dis. 2016; 22(5): 862-5. PubMed

Ismail N, Bloch KC, McBride JW. Human ehrlichiosis and anaplasmosis. Clin Lab Med. 2010; 30(1): 261-92. PubMed

Romero JR, Simonsen KA. Powassan encephalitis and Colorado tick fever. Infect Dis Clin North Am. 2008; 22(3): 545-59, x. PubMed

Sanchez E, Vannier E, Wormser GP, Hu LT. Diagnosis, Treatment, and Prevention of Lyme Disease, Human Granulocytic Anaplasmosis, and Babesiosis: A Review JAMA. 2016; 315(16): 1767-77. PubMed

St Clair K, Decker CF. Ehrlichioses: anaplasmosis and human ehrlichiosis. Dis Mon. 2012; 58(6): 346-54. PubMed

Walker DH, Paddock CD, Dumler S. Emerging and re-emerging tick-transmitted rickettsial and ehrlichial infections. Med Clin North Am. 2008; 92(6): 1345-61, x. PubMed

Medical Reviewers

Last Update: June 2016