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Summary Background Human babesiosis is an emerging zoonosis. “ Babesia venatorum ” has been identified in only four asplenic men and a child so far. We aimed to describe the epidemiological, clinical, and laboratory characteristics of a series of cases with “ B venatorum ” infection identified in a sentinel hospital in China. Methods We recruited participants with a recent tick bite at Mudanjiang Forestry Central Hospital, Heilongjiang province, China. Cases were diagnosed through PCR followed by sequencing, microscopic identification, or isolation by animal inoculation, or both. Findings 48 individuals (30 women or girls; median age 45 years, range 7 months to 75 years) with “ B venatorum ” infection were identified. 32 of these individuals were confirmed cases and 16 were probable cases. None of the 48 cases had received a blood transfusion or had a splenectomy. Geographically, cases were distributed diffusely throughout the hospital catchment area. Of the 32 confirmed cases, 21 (66%) presented with a fever, 13 (41%) with a headache, 12 (38%) with myalgia or arthralgia, and three (9%) with chills. 14 (44%) patients had fatigue, eight (25%) had dizziness, and eight (25%) had hypersomnia. Six (19%) patients had an erythematous non-pruritic rash around the tick-bite site and two (6%) had lymphadenopathy. Seven (22%) and four (13%) patients had anaemia and thrombocytopenia, respectively, and seven (50%) of 14 patients with confirmed infection had increased hepatic transaminase concentrations. In the confirmed cases, concentrations of intercellular adhesion molecule 3 (p<0·001), P-selectin (p<0·05), and platelet endothelial cell adhesion molecule 1 (p<0·001) were significantly reduced, whereas tumour necrosis factor α (p<0·01) and vascular cell adhesion molecule 1 (p<0·001) were significantly increased. Interpretation “ B venatorum ” infection should be included in the differential diagnosis of patients with a tick-exposure history in areas where this pathogen has previously been identified in ticks or people. Funding Natural Science Foundation of China and Mega-Project for Infectious Diseases. [ABSTRACT FROM AUTHOR]