Babesiosis

Key Features

Essentials of Diagnosis

• History of tick bite or exposure to ticks

• Fever, flu-like symptoms, anemia

• Intraerythrocytic parasites on Giemsa-stained blood smears

• Positive serologic tests

General Considerations

• An uncommon intraerythrocytic infection caused mainly by Babesia species and transmitted by Ixodes ticks

• Most cases in the United States occurs in the coastal northeast, with some cases also in the upper midwest

• The incidence of the disease appears to be increasing in some areas

  • Caused by Babesia divergens in Europe

  • Caused by Babesia venatorum in China

• Can be transmitted by blood transfusion, but blood supplies are not screened

• A survey of a large set of blood samples from endemic regions of the United States identified ~0.4% as potentially infectious for B microti

Clinical Findings

• Serosurveys suggest that asymptomatic infections are common in endemic areas

• With B microti infections

  • Symptoms appear 1 to several weeks after a tick bite

  • Parasitemia is evident after 2–4 weeks

• Typical flu-like illness develops gradually and is characterized by

  • Fever

  • Malaise

  • Fatigue

  • Headache

  • Anorexia

  • Myalgia

• Other findings may include nausea, vomiting, abdominal pain, arthralgia, sore throat, depression, emotional lability, anemia, thrombocytopenia, elevated transaminases, and splenomegaly

• B divergens infections

  • Most cases seen in Europe in patients who have had splenectomy

  • These infections progress rapidly with

    • High fever

    • Severe hemolytic anemia

    • Jaundice

    • Hemoglobinuria

    • Acute kidney injury

  • Mortality rates are over 40%

Diagnosis

• Identification of the intraerythrocytic parasite on Giemsa-stained blood smears establishes the diagnosis

• Repeated smears are often necessary because well under 1% of erythrocytes may be infected, especially early in infection, although parasitemias can exceed 10%

• Diagnosis can also be made by PCR, which is more sensitive than blood smear

• An indirect immunofluorescent antibody test for B microti is available from the CDC

  • Antibody is detectable within 2–4 weeks after the onset of symptoms and persists for months

  • A four-fold increase in antibody titer between acute and convalescent sera confirms acute infection

Treatment

Medications

• Standard therapy for mild to moderate disease is a 7-day course of atovaquone (750 mg orally every 12 hours) plus azithromycin (600 mg orally once daily), which is equally effective and better tolerated than the alternative regimen, a 7-day course of quinine (650 mg orally three times daily) plus clindamycin (600 mg orally three times daily)

• However, there is more experience using quinine plus clindamycin, and this regimen is recommended by some experts for severe disease

Therapeutic Procedures

• Exchange transfusion has been used successfully in severely ill asplenic patients and those with parasitemia > 10%

Outcomes

Complications

• Severe complications are most likely to ...