1793. Clinical and molecular evidence of Atovaquone resistance in Babesia microti infection associated with Rituximab
Session: Oral Abstract Session: Resistance is Futile
Saturday, October 29, 2016: 10:43 AM
Room: 288-290
Background: Clinical treatment failure has previously been reported in immunocompromised patients receiving atovaquone (ATV) and azithromycin (AZ) for babesiosis. ATV-resistance is associated with treatment failures of ATV/proguanil in Plasmodium falciparum infections and has been presumed in treatment failures in babesiosis in immune compromised patients receiving ATV/AZ. The cytochrome b (cytb) gene is known to be the molecular target of ATV. We describe a case of babesiosis in an immunocompromised patient with ATV/AZ treatment failure associated with mutations in the cytb gene that developed on therapy.

Methods: DNA was isolated from patient samples and the cytb gene amplified using a High Fidelity DNA polymerase. The amplicons were sequenced using Sanger sequencing. Samples were obtained from different points of the patient’s clinical course. Four control samples were obtained from B.microti positive specimens collected from 2013 to 2015.

Results: An 81-year-old male with chronic lymphocytic leukemia developed hemolytic anemia initially treated with rituximab and steroids. Upon diagnosis of babesiosis by smear, the patient received 6 weeks of ATV/AZ, but 1.5 months after cessation, relapsed with positive blood smears and was re-started on ATV/AZ. While receiving the second course of ATV/AZ, the patient was symptomatic and developed worsening hemolytic anemia with persistent parasitemia (0.1-1%). Clinical and microbiological resolution was ultimately achieved with high-dose AZ, the addition of ATV/proguanil and doxycycline 9 months after diagnosis and 6 months after treatment re-initiation. Through our sequencing efforts we identified two synonymous mutations compared to the reference B. microti genome (plasmodb.org) and a non-synonymous mutation near the presumed ATV binding site in the cytb gene. The mutation was not present in archived patient blood samples at the time of diagnosis, but was present in later samples collected during the patient’s recrudescent illness. All control samples contained only the wild-type allele.

Conclusion: To the best of our knowledge, we describe the first case of Babesia microti ATV-resistance in a human patient that appeared to arise de novo during the patient’s prolonged treatment course.

Matthew S. Simon, MD, MS1,2, Lars Westblade, PhD2, Richard Furman, MD3, Audrey Schuetz, MD4, Stephen Jenkins, PhD5 and Laura Kirkman, MD6, (1)NewYork-Presbyterian Hospital, New York, NY, (2)Weill Cornell Medicine, New York, NY, (3)Weill Cornell Medical College, New York, NY, (4)Mayo Clinic, Rochester, MN, (5)New York-Presbyterian Weill Cornell Medical Center, New York, NY, (6)Weill Cornell Medical College-New York Presbyterian Hospital, New York, NY

Disclosures:

M. S. Simon, None

L. Westblade, None

R. Furman, None

A. Schuetz, None

S. Jenkins, None

L. Kirkman, None

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