736 - Babesia microti: A study of 38 cases

Background: Babesia microti is an intraerythrocytic  infection transmitted by Ixodes scapularis in Eastern United States. The same vector transmits Borrelia burgdorferi, Anaplasma phagocytophilum, B miyamotoi and Powassan virus resulting in mixed infections. Spleen involvement, blood abnormalities and abnormal liver functions are common in babesiosis. Here we present the clinical findings of 38 B microti (smear or serology positive) patients.

Methods:  
We retrospectively evaluated charts of 38 patients, 20 male and 18 female, smear or serology positive for B. microti in our health network from 9 hospitals in Eastern Pennsylvania and one in adjacent Warren county New Jersey.

Results: Eleven had B microti and Lyme co-infections (9 western blot positive, 2 with erythema migrans) and 2 mixed infections with A. phagocytophilum (PCR+). Only 2 gave a history of a tick bite. Fourteen presented with fever. 9 were Babesia  smear positive. All 9 smear positive patients had fever, 7  were anemic, 6 leukopenic and 8 had increased liver enzymes. Six out of 14 with fever and 6 out of 9 smear positive patients had low platelet counts. Two  with left upper abdominal discomfort likely due to splenic inflammation  were initially misdiagnosed as left pyelonephritis. One had splenomegaly. Both had anemia and thrombocytopenia. A patient with a low IGG titer 1:10 for B microti and chronic ITP with a platelet count 102,000 (NL 140-200,000) had a 1 cm splenic artery aneurysm. Four western blot negative patients 2 with  joint pain and 2 with radiculopathy were not counted as mixed infections. A Lyme co-infected patient had sinus tachycardia and ST, T changes in the electrocardiogram suggestive of Lyme myocarditis. All  mixed infections were treated with a combination of atovaquone, azithromycin and doxycycline, including one patient initially on quinine and clindamycin switched due to side effects.

Conclusion: I.scapularis transmitted mixed infections are not uncommon. The majority  were due to B microti and B burgdorferi. Fever was the most common presentation in symptomatic patients. Anemia, leukopenia, thrombocytopenia and elevated liver enzymes were common in  smear positive patents. Babesiosis should be suspected in patients presenting with left upper abdominal pain in tick endemic areas. Most  did not give a history of a tick bite.