Abstract: Objective   To identify the pathogen and make diagnosis on a case who was misdiagnosed as malaria.  Methods  Clinical and epidemiological information of the suspected case was collected. Blood samples during hospitalization were collected and examined microscopically. Genomic DNA from the blood samples was amplified by Babesia 18S RNA genus- and species- specific primers, respectively, and the amplified products were used in sequencing and BLAST sequence analysis.  Results  The case had a fever over 20 days repeatedly with anaemia (RBC 2.59×1012，HB 5.5 g/L) and hepatosplenomegaly. The unidentified parasites were found in the bone marrow and blood smear after Giemsa staining. Epidemiological information revealed that this case had a history of blood transfusion and tick bites. 1 625 bp and 449 bp band generated by PCR amplification from blood sample using Babesia genus- and species-specific primers, and the sequence homology was 99% in comparison to Babesia microti (AB241632) with BLAST analysis. Conclusion  The clinical information, epidemiological history, and the PCR identification confirm the diagnosis of Babesia microti infection.

Key words: Human, Babesia microti, Infection, Diagnosis