Objective To find out the importance of human bocavirus (HBoV) as an infectious agent for population in Beijing, China. Seroprevalence study was conducted by using expressed recombinant major capsid VP2 protein as an antigen.Methods Serum specimens collected from infants and children who visited the Children's Hospital Affiliated to the Capital Institute of Pediatrics for health check-up and adults visiting the Xuanwu Hospital, Beijing for diseases other than respiratory infections from April 1996 to March 1997 were used for the investigation. The major capsid protein VP2 from HBoV was expressed in E. coli strain BL21 (DE3) with the transformed PET30b vector inserted with full-length VP2 gene of HBoV and the specific antigenicity of this expressed protein was validated by previous study. Western blotting was used to detect specific IgG antibody against HBoV in collected serum specimens diluted to 1:200. Mock expressed protein was E. coli cells strain BL21 (DE3) with the transformed PET30b vector without insert. Anti-His monoclonal antibody and rabbit anti-HBoV VP2 polypeptides hyper-immune serum were used as positive control for antibody detection.Results Out of 677 serum specimens tested, 400 (59.1% ) were positive for HBoV by Western blotting. About 45.3% (34/75) of the newborns under 1 month of age had anti-HBoV antibodies, and antibody positive rates were decreased in age groups of 1 and 2 months (41.4% and 31.3%, respectively) then increased in the following ages from 6 months to 7 years old ( from 45.6% to 69.7% ). The antibody positive rates were maintained at a relatively constant level ( about 70% ) in the age groups from 7 years to 40 years of age and became lower ( 61.8% - 62. 8% ) in those over 50 years.Conclusions The high seroprevalence of antibody against recombinant HBoV VP2 protein and early age antibody acquisition indicate that HBoV has been circulating in population of Beijing, China as early as in 1996 and most of children had been exposed to HBoV by the age of 7 years. Infants under the age of 6 months were susceptible to this virus.
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