This study is a double-blind, randomized, multisite, placebo-controlled trial comparing the safety and efficacy of TQ versus placebo in patients hospitalized for babesiosis with low risk for relapsing disease who will also be administered a standard-of-care antimicrobial regimen (A/A) that is recommended in the 2020 IDSA guideline on the diagnosis and management of babesiosis.

This study is a double-blind, randomized, multisite, placebo-controlled trial comparing the safety and efficacy of TQ versus placebo in patients hospitalized for babesiosis with low risk for relapsing disease who will also be administered a standard-of-care antimicrobial regimen (A/A) that is recommended in the 2020 IDSA guideline on the diagnosis and management of babesiosis.

Patients hospitalized for a diagnosis of babesiosis, who have received A/A for <48 hours (h) prior to randomization or are about to receive A/A, will be asked to provide written informed consent and will undergo eligibility screening including medical history, physical examination, prior and concomitant medications, blood chemistry and hematology, glucose-6-phosphate dehydrogenase (G6PD) deficiency testing, blood smear for diagnostic confirmation of babesiosis, pregnancy testing for females of child-bearing potential, and assessment of risk factors for relapsing babesiosis. The screening period will last a maximum of two days. The first day of dosing with TQ or placebo will be Day 1 and will be done while the patient is still hospitalized.

Inclusion Criteria:

• Male or female, aged ≥ 18 years.
• Laboratory confirmed infection with Babesia.
• Exhibiting at least one self-reported clinical symptoms of babesiosis.
• Able and willing to give written informed consent.
• Expected to be hospitalized at the time of or following informed consent and still hospitalized on the day of randomization and start of investigational products.
• Willing to complete the study activities and assessments.
• Must agree not to enroll in another study of an investigational agent prior to completion of the study.
• Able to take oral medications.
• If female of reproductive age, must agree to use an acceptable method of birth control.
• Adequate venous access.
• Blood hemoglobin ≥ 7 g/dL.

Exclusion Criteria:

• Have any contraindications to TQ.
• Have any contraindication for azithromycin or atovaquone.
• Any concomitant significant illness unrelated to babesiosis.
• Receipt of any experimental treatment for babesiosis.
• Taking any excluded concomitant medication.
• Current or planned treatment with quinine while participating in the study.
• Positive pregnancy test.
• If A/A was initiated more than 48h prior to randomization and parasitemia is not >1%.
• Azithromycin or atovaquone administered in the last 12 months to treat babesiosis, and, in the opinion of the investigator, high likelihood that current infection represents a relapse or continuation of disease.

Double blind