What is babesiosis?

Babesiosis: A Tick-Borne Parasitic Disease

Babesiosis is an intraerythrocytic protozoal infection caused primarily by Babesia microti in the United States, transmitted by Ixodes scapularis ticks, with clinical manifestations ranging from asymptomatic infection to life-threatening disease characterized by hemolytic anemia, organ failure, and potential death. 1

Etiology and Transmission

• Caused by intraerythrocytic protozoa of the genus Babesia
• In the United States, B. microti is the most common species 1
• In Europe, B. divergens is more prevalent 2
• Other species causing human infection include B. duncani in California and Washington, and B. divergens-like organisms in Missouri, Kentucky, Washington, and Arkansas 1
• Primarily transmitted by Ixodes scapularis ticks, which may also transmit Lyme disease (Borrelia burgdorferi) and anaplasmosis (Anaplasma phagocytophilum) 1
• Can also be transmitted through blood transfusion or, rarely, transplacentally 3

Clinical Features

Babesiosis presents with a spectrum of clinical manifestations:

• Asymptomatic infection: Approximately 25% of infected adults and 50% of children may be asymptomatic or have such mild illness that diagnosis occurs incidentally 1

• Mild to moderate disease: Most symptomatic patients experience:

  • Viral-like illness with fever, chills, sweats
  • Myalgia, arthralgia
  • Fatigue, malaise
  • Anorexia, nausea, vomiting 1

• Physical examination findings:

  • Fever
  • Splenomegaly
  • Hepatomegaly
  • Jaundice 1

• Laboratory abnormalities:

  • Hemolytic anemia with elevated reticulocyte count
  • Thrombocytopenia
  • Proteinuria
  • Elevated liver enzymes
  • Elevated blood urea nitrogen and creatinine 1

• Severe disease: Can include complications such as:

  • Acute respiratory failure
  • Disseminated intravascular coagulation
  • Congestive heart failure
  • Coma
  • Renal failure 1

Risk Factors for Severe Disease

• Immunocompromised status
• Asplenia (lack of a spleen)
• Malignancy
• HIV infection
• Age >50 years 1

Diagnosis

Diagnosis of babesiosis requires a combination of:

1. Epidemiologic information:

   • Residence in or travel to endemic areas (northeastern and upper midwestern United States)
   • Blood transfusion within previous 9 weeks 1

2. Laboratory testing:

   • Gold standard: Microscopic examination of Giemsa-stained thin blood smears showing intraerythrocytic parasites 1
   • Parasites may be sparse (often <1% of erythrocytes), requiring careful examination 4
   • Thick blood films may help detect parasites but may not differentiate between Babesia and Plasmodium species 1
   • Serologic testing: Useful supplementary evidence as robust antibody response characterizes infection 4
   • PCR: Comparable sensitivity and specificity to microscopy for detection of babesial DNA 4

Treatment

Treatment should be based on disease severity:

Mild to Moderate Disease

First-line therapy: Atovaquone (750 mg every 12 hours) plus azithromycin (500 mg on day 1, then 250 mg daily) for 7-10 days 5

• Associated with fewer adverse effects than alternative regimens
• Equal effectiveness to clindamycin plus quinine 5, 4

Alternative therapy: Clindamycin (600 mg every 8 hours) plus quinine (650 mg every 8 hours) for 7-10 days 5

• Higher rate of adverse effects including tinnitus, diarrhea, and decreased hearing 5
• Approximately 75% of patients experience adverse drug reactions 1
• One-third may need to decrease dose or discontinue medication 1

Severe Disease

For patients with:

• Parasitemia >10%
• Significant hemolysis
• Organ dysfunction

Management includes:

• Antimicrobial therapy as above
• Consideration of partial or complete red blood cell exchange transfusion 5, 3
• Higher doses of azithromycin (600-1000 mg daily) may be needed 5
• Consultation with infectious disease specialists and hematologists is recommended 5

Note: While parasitemia >10% has traditionally been used as a threshold for exchange transfusion, clinical status and evidence of end-organ failure should be considered in the decision to perform this procedure 3

Monitoring and Treatment Response

• Clinical improvement should occur within 48-72 hours of initiating appropriate therapy 5
• Monitor for:
  • Resolution of fever
  • Improvement in laboratory parameters
  • Decrease in parasitemia levels until clearance 5

Prevention

• Avoid areas where ticks, deer, and mice thrive (tall grass and brush)
• Use protective clothing and tick repellents
• Check entire body for ticks daily
• Promptly remove attached ticks 4

Key Pitfalls to Avoid

1. Misdiagnosis: Babesiosis can be confused with malaria due to similar intraerythrocytic appearance
2. Overlooking co-infections: I. scapularis ticks may transmit Lyme disease and anaplasmosis along with babesiosis
3. Delayed diagnosis: Parasites may be sparse and easily missed on blood smears
4. Inappropriate treatment: Doxycycline is effective for anaplasmosis but not for babesiosis 5
5. Failure to recognize severe disease: Immunocompromised patients are at higher risk for severe, potentially fatal disease