Babesia microti

Background

• Causes babesiosis

Microbiology

• Tickborne protozoa
• Different species of Babesia exist
• Seen as Maltese cross on blood smear

Epidemiology

• Tickborne by Ixodes scapularis
• Reservoir is white-footed mice
• Can be transmitted by blood transfusion and, rarely, transplacentally (5 cases)
• More common in the northeastern US, including Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island, and Wisconsin
  • Highly endemic in Nantucket, Martha's Vineyard, the Elizabeth Islands, Block Island, Shelter Island, eastern Long Island, an Fire Island
• Has been found in Canada as of 2013, with several case reports from Manitoba and on case report of Babesia duncani infection in souther Ontario1
• Typically takes 36 hours or longer of tick attachment to be transmitted to human host

Other Species

• B. duncani and B. duncani-type organisms are present in the Pacific Coast
• B. divergens in Europe; rarely B. venatorum

Clinical Manifestations

• Incubation period 1 to 6 weeks
  • Diagnosis can be delayed
  • There are some cases of asymptomatic parasitemia
  • May experience recrudescence after immunosuppression
• Symptoms include fatigue, weakness, and malaise, followed by fever and chills, arthralgias, or nausea
  • Fever may be intermittent or persistent, and can be high
• Can also cause nuchal rigidity, sore throat, dyspnea, weight loss, vomiting, diarrhea, and dark urine
• Occasionally causes emotional lability, depression, hyperesthesia, photophobia, conjunctival injection, abdominal pain, petechiae, and ecchymoses
• May have erythema chronicum migrans rash in cases of coinfection
• Bloodwork shows anemia, jaundice, and other evidence of hemolysis, often with positive direct antiglobulin test
  • Also thrombocytopenia and liver enzyme abnormalities
  • If neutropenia, suggests coinfection with anaplasmosis

Prognosis and Complications

• 40% develop complications, including ARDS, DIC, CHF, coma, AKI, splenic rupture
• More severe illness in patients with asplenia, X-linked agammaglobulinemia, malignancy, HIV with low CD4 count, TNF-α inhibitors, and immunosuppression for transplantation, B-cell lymphoma, or autoimmune disorders

Congenital Infection

• Five cases
• Symptom onset around 3 to 6 weeks
• Parasitemia 2-15% on diagnosis

Other Babesia species

• B. divergens usually in aplenic patients, causing fulminant disease

Diagnosis

• Parasites visualized on blood film, with parasitemia from 1 to 20% but as high as 85% in splenectomized patients

Management

• Asymptomatic parasitemia: no treatment necessary unless immunocompromised or persists for longer than 3 months
• Mild: atovaquone 750 mg PO q12h plus azithromycin 500-1000 mg PO once followed by 250-500 mg PO daily for 7 to 10 days
• Severe: clindamycin 300-600 mg IV q6h or 600 mg PO q8h plus quinine 650 mg PO q6-8h
  • ± RBC exchange transfusion if parasitemia ≥10%, severe hemolysis, or pulmonary, renal, or hepatic failure
• B. divergens: RBC exchange transfusion plus clindamycin plus quinine
• Duration
  • 7 to 10 days for most
  • Can relapse when immunocompromised, so these patients need 6+ weeks including 2+ weeks without parasitemia