Activities of artesunate-based combinations and tafenoquine against Babesia bovis in vitro and Babesia microti in vivo

<jats:title>Abstract</jats:title><jats:sec> <jats:title>Background</jats:title> <jats:p>Babesiosis represents a veterinary and medical threat, with a need for novel drugs. Artemisinin-based combination therapies (ACT) have been successfully implemented for malaria, a human disease caused by related parasites, <jats:italic>Plasmodium</jats:italic> spp. The aim of this study was to investigate whether ACT is active against <jats:italic>Babesia in vitro</jats:italic> and <jats:italic>in vivo</jats:italic>.</jats:p> </jats:sec><jats:sec> <jats:title>Methods</jats:title> <jats:p>Mefloquine, tafenoquine, primaquine, methylene blue and lumefantrine, alone or in combination with artesunate, were tested <jats:italic>in vitro</jats:italic> against <jats:italic>Babesia bovis</jats:italic>. Parasite growth was verified using a SYBR green I-based fluorescence assay. Mice infected with <jats:italic>Babesia microti</jats:italic> were treated with mefloquine or tafenoquine, alone or in combination with artesunate, and parasitemia was verified by microscopy and PCR.</jats:p> </jats:sec><jats:sec> <jats:title>Results</jats:title> <jats:p>All drugs, except lumefantrine, showed <jats:italic>in vitro</jats:italic> activity against <jats:italic>B</jats:italic>. <jats:italic>bovis</jats:italic>, with methylene blue showing the most potent activity (concentration 0.2 μM). Combination with artesunate led to improved activity, with mefloquine showing a striking 20-fold increase in activity. Tafenoquine (10 mg/kg, base), combined or not with artesunate, but not mefloquine, induced rapid clearance of <jats:italic>B</jats:italic>. <jats:italic>microti in vivo</jats:italic> by microscopy, but mice remained PCR-positive. Blood from mice treated with tafenoquine alone, but not with tafenoquine-artesunate, was infective for naive mice upon sub-inoculation.</jats:p> </jats:sec><jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Tafenoquine, and most likely other 8-aminoquinoline compounds, are promising compounds for the development of ACT for babesiosis.</jats:p> </jats:sec>