Babesiosis

Key Features

• Babesia microti is a malaria-like protozoan that infects humans bitten by infected Ixodes scapularis (deer tick)

• After inoculation, the protozoan penetrates erythrocytes and starts an asynchronous cycle that causes hemolysis

• In the United States, the majority of cases occur in the Northeast and upper Midwest from May to October

• Infection is a transfusion-transmissible disease

• Incubation period is 1–4 weeks after tick bite, or 1–9 weeks after blood transfusion

Clinical Findings

• Approximately half of infected children are asymptomatic

• Symptoms are nonspecific and most commonly include

  • Sustained or cyclic fever up to 40.9°C

  • Shaking chills

  • Sweats

• Other associated nonspecific symptoms include

  • Malaise

  • Fatigue

  • Anorexia

  • Arthralgias

  • Myalgias

  • Headache

• Physical examination findings are usually minimal but may include

  • Hepatosplenomegaly

  • Jaundice

  • Dark urine

• Disease is usually self-limited, causing symptoms for 1–2 weeks with fatigue that may persist for months

• Hemolytic anemia and thrombocytopenia are common

Diagnosis

• Babesial parasites are identified in blood by microscopic evaluation of thin or thick blood smears or by polymerase chain reaction (PCR) amplification of babesial DNA

• Babesia parasites are intraerythrocytic organisms that resemble Plasmodium falciparum ring forms

• The tetrad form (Maltese cross), if visualized, is pathognomonic

• Specific serologic tests are also available through the Centers for Disease Control and Prevention (CDC)

Treatment

• Azithromycin (10 mg/kg up to 500 mg on the first day, followed by 5 mg/kg up to 250 mg/day) in combination with atovaquone (20 mg/kg, up to 750 mg, twice a day) for 7–10 days

  • Treatment of choice for mild to moderate disease

  • Causes fewer adverse side effects than other regimens.

• Clindamycin (10 mg/kg, up to 600 mg, every 8 hours) in combination with quinine (8 mg/kg, up to 650 mg, every 8 hours) is standard of care for severely ill patients

• Longer courses of treatment may be needed in immunocompromised patients

• Partial or complete RBC exchange transfusion is indicated for persons with

  • Severe babesiosis, as indicated by high-grade parasitemia (≥ 10%)

  • Significant hemolysis

  • Renal, hepatic, or pulmonary compromise