The apicomplexan intraerythrocytic parasite Babesia microti is an emerging human pathogen and the primary cause of human babesiosis, a malaria-like illness endemic in the United States. The pathogen is transmitted to humans by the tick vector, Ixodes scapularis, and by transfusion of blood from asymptomatic B. microti-infected donors. Babesiosis is a major public health concern because the population at risk for severe disease (people over the age of 50 and of any age with compromised immune systems) is increasing. Presently, drug combinations of azithromycin+atovaquone or clindamycin+quinine are recommended therapies. These drug combinations were first evaluated for their anti-babesia activity because of their known antimalarial activity. With these drugs and other supportive measures such as exchange transfusion, the mortality rate is 9% in infected patients requiring hospitalization and approaches 28% in immunocompromised hosts. Patients who survive may experience recrudescent parasitemia for more than a year, requiring more prolonged therapy. The reasons that Babesia can persist despite drug therapy remain unknown. A better understanding of the parasite metabolism, diversity, virulence and tissue distribution are critical for the development of more effective therapies for treatment of human babesiosis. Towards this goal, we have completed genomic and transcriptomic analyses and initiated thorough annotation of the genomes and reconstruction of the metabolic machineries of seven B. microti clinical isolates. Our preliminary findings indicate that B. microti exhibits genotypic variations among strains. These variations may account for their notable differences in rate of proliferation and host selectivity (mice vs hamsters). We have also identified two key metabolic pathways, the non-mevalonate (MEP) pathway and the folate biosynthesis pathway (FBP), which can be targeted by drugs already approved by the FDA. In order to fully characterize the efficacy of these drugs against B. microti infection in vivo, a mouse model of B. microti infection must be more clearly defined in terms of sites of parasite persistence that may lead to recrudescence of parasitemia. Accordingly, this proposal aims to (1) define in mice the kinetics of parasitemia and sites of persistence of two prototype B. microti strains isolated from non-immunocompromised patients who experienced mild or severe disease;and (2) assess the efficacy of drugs that target the MEP and FBP pathways of B. microti to resolve parasitemia and eliminate infection. Successful completion of these exploratory studies will help define mechanisms underlying B. microti pathogenesis and set the stage for future clinical studies to evaluate the efficacy of these drugs for treatment of human babesiosis in situations when current therapies fail.

Public Health Relevance

Human babesiosis, a malaria-like disease caused by a parasite that is transmitted by ticks or by blood transfusion, can be relatively asymptomatic or lead to severe multisystem illness that can be fatal in people with compromised immune systems. Current drug therapies have significant side effects, may not be effective in severe disease, and are associated with an increasing number of reported therapeutic failures. This proposal uses a mouse model of babesiosis to define where the parasite persists in mammals and to test whether novel drugs, already FDA-approved for other diseases, might provide more effective options for treatment of this infection.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Exploratory/Developmental Grants (R21)
Project #
Application #
Study Section
Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
Program Officer
Rogers, Martin J
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Yale University
Internal Medicine/Medicine
Schools of Medicine
New Haven
United States
Zip Code
Silva, Joana C; Cornillot, Emmanuel; McCracken, Carrie et al. (2016) Genome-wide diversity and gene expression profiling of Babesia microti isolates identify polymorphic genes that mediate host-pathogen interactions. Sci Rep 6:35284
Carpi, Giovanna; Walter, Katharine S; Mamoun, Choukri Ben et al. (2016) Babesia microti from humans and ticks hold a genomic signature of strong population structure in the United States. BMC Genomics 17:888
Cornillot, Emmanuel; Dassouli, Amina; Pachikara, Niseema et al. (2016) A targeted immunomic approach identifies diagnostic antigens in the human pathogen Babesia microti. Transfusion 56:2085-99
Lawres, Lauren A; Garg, Aprajita; Kumar, Vidya et al. (2016) Radical cure of experimental babesiosis in immunodeficient mice using a combination of an endochin-like quinolone and atovaquone. J Exp Med 213:1307-18
Vannier, Edouard G; Diuk-Wasser, Maria A; Ben Mamoun, Choukri et al. (2015) Babesiosis. Infect Dis Clin North Am 29:357-70
Garg, Aprajita; Wesolowski, Donna; Alonso, Dulce et al. (2015) Targeting protein translation, RNA splicing, and degradation by morpholino-based conjugates in Plasmodium falciparum. Proc Natl Acad Sci U S A 112:11935-40