Optimization of an Evaluation Method for Anti-Babesia microti Drug Efficacy

Babesiosis is an emerging zoonotic disease that is typically caused by Babesia microti infection. Clinical treatment of B. microti infection is challenging; hence, it is crucial to find new effective drugs. The current laboratory screening methods for anti-B. microti drugs are not optimized. We conducted drug-suppressive and drug-therapeutic tests to investigate whether use of an immunosuppressant and the target gene-based qPCR are helpful to reduce the number of animals affected and to improve parasite detection in an immunocompetent mouse model. These results were verified by subpassage test. In the drug-suppressive test, no B. microti were observed after immunosuppressant administration or in subpassage mice in the 100 mg/kg robenidine hydrochloride (ROBH) group. The opposite results were observed in the control, 50 mg/kg ROBH, atovaquone (ATO) + azithromycin (AZM), and proguanil hydrochloride (PGH) groups. Significant differences were observed in the EIR and target gene relative values (both P < 0.001) between the control group and any ROBH groups. In the drug-therapeutic test, recrudescence occurred in the 50 mg/kg ROBH, ATO+AZM, and control groups. This was not observed in the 100 mg/kg ROBH group after immunosuppressant administration. Similar findings were observed in the subpassage test. This suggests that a 4-day anti-B. microti drug-suppressive test can be used in preliminary drug screening. Potentially effective drugs can be verified by immunosuppressant test in subsequent drug-therapeutic tests. Thus, a laboratory evaluation method of anti-B. microti drug efficacy was optimized, which is highly accurate and requires a short drug screening time.