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Background: Human babesiosis is an emerging health problem in China., Methods: Babesia were identified in ticks, sheep, and humans in northeastern China using polymerase chain reaction (PCR) followed by genetic sequencing. We enrolled residents who experienced a viral-like illness after recent tick bite or were healthy residents. We defined a case using the definition for babesiosis developed by the US Centers for Disease Control and Prevention., Results: A Babesia crassa-like agent was identified in Ixodes persulcatus and Haemaphysalis concinna ticks using PCR followed by sequencing. The agent was characterized through phylogenetic analyses of the 18S rRNA gene, the β-tubulin gene, and the internal transcribed spacer region. We tested sheep as a possible reservoir and found that 1.1% were infected with the B. crassa-like agent. We screened 1125 human participants following tick bites using B. crassa-specific PCR and identified 31 confirmed and 27 suspected cases. All the patients were previously healthy except for 1 with an ovarian tumor. Headache (74%), nausea or vomiting (52%), and fever (48%) were the most common clinical manifestations of confirmed cases. Six of 10 cases remained PCR positive for B. crassa-like infection 9 months after initial diagnosis. Asymptomatic infections were detected in 7.5% of 160 local residents., Conclusions: We identified B. crassa-like infection in people in northeastern China that caused mild to moderate symptoms. The possibility of more severe disease in immunocompromised patients and of transmission through the blood supply due to asymptomatic infections justifies further investigation of this reported infection.

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., (Copyright © 2015 Elsevier Ltd. All rights reserved.)