Case history
Case history #1
A 35-year-old woman living in coastal Connecticut finds a tick attached behind her knee in August. Her primary care provider removes the tick, notes it to be an engorged Ixodes scapularis nymph, and gives her 1 dose of doxycycline for prophylaxis of Lyme disease. Two weeks later, the woman develops gradual onset of malaise and fatigue, followed by fever. She visits her primary care provider again, who orders a CBC, liver profile, and serology for antibodies to Borrelia burgdorferi and Anaplasma phagocytophilum and obtains a Giemsa-stained thin blood smear. The blood smear reveals small, intraerythrocytic ring forms consistent with Babesia microti. The patient receives a 7-day course of azithromycin and atovaquone, with complete resolution of symptoms. Antibodies to Borrelia burgdorferi and Anaplasma phagocytophilumare not detected.
Case history #2
A 65-year-old man living in Nantucket, Massachusetts and receiving rituximab for lymphoma presents to the emergency department of his local hospital with 2 days of fever and shaking chills. He is noted to have severe anemia, proteinuria, and hemoglobinuria. The patient is admitted to the hospital, and broad-spectrum antibiotics are started for presumed bacterial infection. Soon after admission, he develops respiratory failure, requiring mechanical ventilation. A blood smear obtained on day 2 reveals intraerythrocytic ring forms with parasitemia of 20%. The patient has not traveled away from Nantucket in several years. Treatment for babesiosis with intravenous clindamycin and oral quinine is initiated, and the patient also receives exchange transfusions. Parasitemia decreases and the patient no longer needs mechanical ventilation by day 4. He is discharged home after 14 days, but his outpatient course is complicated by relapsing parasitemia requiring additional courses of antibabesial treatment.
Other presentations
Most infections of Babesia microti in young healthy people are subclinical or mild and are likely to often go undiagnosed. Because unengorged Ixodes scapularis nymphs are quite small (2 mm), most patients do not recall receiving a tick bite.
Clinical infections are more common in asplenic patients, those with concurrent Lyme disease, patients with immunosuppression (either due to HIV infection or drug induced), or older patients. Symptoms appear 1 to 4 weeks after the tick bite, with a gradual onset of malaise, fatigue, myalgias, arthralgias, shaking, and chills.[5] A sustained or intermittent fever may develop within 1 week of symptom onset. Less frequent symptoms include anorexia, vomiting, cough, abdominal pain, photophobia, conjunctival injection, and a sore throat.[6]
Manifestations such as hemolytic anemia or thrombocytopenia may be severe or life threatening, and disease can rarely also be fatal. Complications include acute respiratory failure, disseminated intravascular coagulation, congestive heart failure, coma, renal failure, and splenic rupture or infarct.[6][7]
Infection with Babesia divergens, which is more commonly found in Europe, occurs mostly in asplenic patients, and is always fulminant and hemolytic.[8] Infections with rarer species, such as Babesia duncani, MO-1 and CA-1, also tend to be fulminant.[4]
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