Enhanced Anti-Babesia Efficacy of Buparvaquone and Imidocarb When Combined with ELQ-316 In Vitro Culture of Babesia bigemina

<b>Background/Objectives:</b><i>B. bigemina</i> is a highly pathogenic and widely distributed tick-borne disease parasite responsible for bovine babesiosis. The development of effective and safe therapies is urgently needed for global disease control. The aim of this study is to compare the effects of endochin-like quinolone (ELQ-316), buparvaquone (BPQ), imidocarb (ID), and the combinations of ID + ELQ-316 and BPQ + ELQ-316, on in vitro survival of <i>B. bigemina.</i><b>Methods:</b> Parasites at a starting parasitemia level of 2%, were incubated with each single drug and a combination of drugs, ranging from 25 to 1200 nM of concentration over four consecutive days. The inhibitory concentrations, 50% (IC50%) and 99% (IC99%), were estimated. Parasitemia levels were evaluated daily using microscopic examination. Data were statistically compared using the non-parametrical Kruskall-Wallis test. <b>Results:</b> All drugs tested significantly inhibited (<i>p</i> < 0.05) the growth of <i>B. bigemina</i> at 2% parasitemia. The combination of ID + ELQ-316 exhibited a lower mean (IC50%: 9.2; confidence interval 95%: 8.7-9.9) than ID (IC50%: 61.5; confidence interval 95%: 59.54-63.46), ELQ-316 (IC50%: 48.10; confidence interval 95%: 42.76-58.83), BPQ (IC50%: 44.66; confidence interval 95%: 43.56-45.81), and BPQ + ELQ-316 (IC50%: 27.59; confidence interval: N/A). Parasites were no longer viable in cultures treated with the BPQ + ELQ-316 combination, as well as with BPQ alone at a concentration of 1200 nM, on days 2 and 3 of treatment, respectively. <b>Conclusions:</b> BPQ and ID increase the babesiacidal effect of ELQ-316. The efficacy of these combinations deserves to be evaluated in vivo, which could lead to a promising and safer treatment option for <i>B. bigemina</i>.