Babesia microti

Indications for Testing

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

Laboratory Testing

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
IFA testing
- High sensitivity and specificity in Babesia detection
- Test of choice for laboratory diagnosis
- 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 HGA

Differential Diagnosis

Plasmodium spp (malaria)
Borrelia burgdorferi (Lyme disease)
Rickettsial disease
- Rickettsia rickettsii (Rocky Mountain spotted fever)
- Rickettsia typhi (typhus)
Ehrlichiosis
Colorado tick fever
Human granulocytic anaplasmosis (HGA)
Brucella spp (brucellosis)
Dengue fever virus
Francisella tularensis (tularemia)
Leptospira spp
Parvovirus

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 the 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 the 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 and 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, resulting in capillary blockage in the spleen, liver, kidneys and central nervous system
Immunocompromised patients may experience persistent or relapsing disease
Complications
- Acute respiratory failure
- Congestive heart failure
- Renal failure

Treatment

Generally treated for at least 7-10 days with one of the following combinations of medications
- Atovaquone and azithromycin
- Clindamycin and quinine (severely ill patients)
  - These drugs are FDA-approved but considered investigational for babesiosis treatment
Some severely ill patients may also require supportive care
- Antipyretics to reduce fever
- Vasopressors to increase blood pressure (if low)
- Blood transfusions
- Exchange transfusions
- Mechanical ventilation
- Dialysis

Prevention

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

Tests generally appear in the order most useful for common clinical situations

Test name: CBC with Platelet Count & Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count with Flow Cell Differential

Use:

Screening test to help differentiate between bacterial and viral disease

Test name: Parasites Smear (Giemsa Stain), Blood

ARUP #: 0049025

Methodology: Stain

Use:

Use in conjunction with B. microti antibody in patients with history of travel or residence in endemic area

Thick smears of hemolyzed blood are most useful for screening purposes in cases with low-level parasitemia; thin smears are used for parasite classification

Limitations:

False-negative results may occur due to low parasite levels

Time-sensitive

Test name: Babesia microti Antibodies, IgG & IgM by IFA

ARUP #: 0093048

Methodology: Semi-Quantitative Indirect Fluorescent Antibody

Use:

Detect B. microti-specific IgG and IgM antibodies in patients with history of travel or residence in endemic area

Additional Tests Available

Test name: Babesia microti Antibody, IgG by IFA

ARUP #: 0093049

Methodology: Semi-Quantitative Indirect Fluorescent Antibody