Cytochrome b Drug Resistance Mutation Decreases Babesia Fitness in the Tick Stages But Not the Mammalian Erythrocytic Cycle

Abstract

Human babesiosis is an emerging tick-borne malaria-like illness caused by Babesia parasites following their development in erythrocytes. Here, we show that a mutation in the Babesia microti mitochondrial cytochrome b (Cytb) that confers resistance to the antibabesial drug ELQ-502 decreases parasite fitness in the arthropod vector. Interestingly, whereas the mutant allele does not affect B. microti fitness during the mammalian blood phase of the parasite life cycle and is genetically stable as parasite burden increases, ELQ-502 R mutant parasites developing in the tick vector are genetically unstable with a high rate of the wild type allele emerging during the nymphal stage. Furthermore, we show that B. microti parasites with this mutation are transmitted from the tick to the host, raising the possibility that the frequency of Cytb resistance mutations may be decreased by passage through the tick vector, but could persist in the environment if present when ticks feed.

Treatment of Human Babesiosis: Then and Now

“…Interestingly, a shorter treatment duration with ELQ-502 alone at 10 mg/kg in B. microti-infected mice resulted in recrudescence [109]. Similarly to the results obtained following treatment with ELQ-271, ELQ-316, and ELQ-334, recrudescence following ELQ-502 shorter treatment duration was associated with GCT → GTT mutation in the Q i site of the BmCytb [109]. Results obtained from the evaluation of ELQ derivatives are summarized in Table 3.…”

“…Following a 10-day treatment course, both the mono-and the combination therapies resulted in radical cure with no recrudescence, and in the case of B. duncani-infected mice, 100% survival [57]. Interestingly, a shorter treatment duration with ELQ-502 alone at 10 mg/kg in B. microti-infected mice resulted in recrudescence [109]. Similarly to the results obtained following treatment with ELQ-271, ELQ-316, and ELQ-334, recrudescence following ELQ-502 shorter treatment duration was associated with GCT → GTT mutation in the Q i site of the BmCytb [109].…”

Effectiveness of Two New Endochin-like Quinolones, ELQ-596 and ELQ-650, in Experimental Mouse Models of Human Babesiosis

“…30 These findings were further confirmed following the discovery of individual mutations in residues in the Q i or Q o sites responsible for resistance to either ELQ or atovaquone, respectively. 32 Accordingly, drug combinations consisting of ELQs and atovaquone have shown strong antibabesial efficacy in vitro and in animal models of babesiosis. 30 To assess the mode of interaction between second-generation ELQs and their prodrugs with atovaquone, we first calculated the FIC 50 for each drug using eq 1 as described in the Methods section, and then we used isobologram analysis to calculate the mean fractional inhibitory concentration (∑FIC50) using eq 2 as described in the Methods section.…”

Babesia microti with multiple resistance mutations detected in an immunocompromised patient receiving atovaquone prophylaxis

“…Genetic variation in B. microti may also be associated with clinical relapse 6 . Several previously described variants include the molecular targets of atovaquone (cytochrome b; cytb) and azithromycin (ribosomal protein L4; rpl4) that potentially confer resistance to these drugs in B. microti 4,[6][7][8][9][10][11] . Atovaquone is known to hinder electron transport in the mitochondria of Plasmodium parasites at the cytochrome b site 12 , which is also the drug's target in other apicomplexan parasites 13 .…”