Babesia microti

Diagnosis

Indications for Testing

  • Strong clinical suspicion in patient with febrile illness after tick exposure or with a high-risk occupation

Laboratory Testing

  • CDC diagnosis recommendations for babesiosis
  • Nonspecific – CBC may demonstrate hemolysis in severe disease
  • Giemsa-stained blood films – in patients from endemic areas
    • Diagnostic, if parasites noted
    • Relatively insensitive due to low parasite level in most patients
    • Thick smears of hemolyzed blood are most useful for screening purposes in cases with low-level parasitemia; thin smears are used for parasite classification
  • Serologic (IFA) testing
    • Test of choice for laboratory diagnosis for patients from endemic areas
    • High sensitivity and specificity in Babesia detection
    • Rises 2-4 weeks after infection and wanes at 6-12 months
    • Strain MO-1 (found in Missouri) and B. duncani (found in Pacific Northwest) will not be detected by B. microti serology
  • PCR – highly sensitive and specific but relatively expensive
    • Available at CDC with limited availability elsewhere
  • In areas of coinfection, consider concurrent testing for Lyme disease and human granulocytic anaplasmosis (HGA)

Differential Diagnosis

Clinical Background

Babesiosis is a zoonosis caused by an intraerythrocytic parasite of the genus Babesia.

Epidemiology

  • Prevalence
    • Found in the same geographic regions as agents responsible for Lyme disease and human granulocytic anaplasmosis (HGA)
      • Most common in Northeast and Midwest U.S.
      • Coinfections of babesiosis, Lyme disease, and HGA occur in 10% of patients
  • Transmission
    • Tick bite – Ixodes spp
      • Vector – Ixodes scapularis (formerly Ixodes dammini)
        • More commonly known as a blacklegged or deer tick (in U.S.)
    • Blood transfusion – rare
    • For more information on causal agents, life cycle, and geographic distribution, see CDC's information on Babesiosis

Organism

  • Protozoal parasite – obligate parasite of red blood cells
  • >100 known species – most common types in U.S. are B. microti and B. divergens

Risk Factors for Severe Disease

  • Splenectomy
  • Immunosuppression
  • Coinfection

Clinical Presentation

  • Most cases of human babesiosis are asymptomatic
  • Symptomatic patients experience fever, headache, nausea, sweats, rigors
    • Symptoms occur 1-6 weeks following tick bite
  • Resemblance to a fulminant malaria-like infection may complicate initial diagnosis
  • Hemolytic anemia and thrombocytopenia may occur in severe disease
    • Parasites fragment red blood cells
      • Results in capillary blockage in the spleen, liver, kidneys, central nervous system
  • Immunocompromised patients may experience persistent or relapsing disease
  • Complications

Prevention

  • Protective clothing (long sleeves and pants) in tick-prone areas
  • DEET on exposed skin

Indications for Laboratory Testing

  • 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
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Screen to help differentiate between bacterial and viral disease

    
Parasites Smear (Giemsa Stain), Blood 0049025
Method: Stain
 Initial test for babesiosis in patients with history of travel or residence in endemic area

False-negative results may occur due to low parasite levels

Time-sensitive

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

Useful if giemsa stain is negative but high suspicion of babesiosis exists

  

If test results are equivocal repeat testing in 10-14 days
Additional Tests Available
 
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Borrelia burgdorferi Antibodies, Total by ELISA 0050216
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay
Borrelia burgdorferi C6 Peptide Antibodies, Total by ELISA 0051044
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay
Anaplasma phagocytophilum (HGA) Antibodies, IgG & IgM 0097303
Method: Semi-Quantitative Indirect Fluorescent Antibody
Babesia microti Antibody, IgG by IFA 0093049
Method: Semi-Quantitative Indirect Fluorescent Antibody
Babesia microti Antibody, IgM by IFA 0093050
Method: Semi-Quantitative Indirect Fluorescent Antibody