Charateristics Of Human Bocavirus Infection In Children In Chognqign Area

BackgroundAcute respiratory tract infections (ARTIs) are most common diseases in children worldwide and a major cause of mortality in children under 5 years old. A broad spectrum of microbial agents account for respiratory tract infections in which viruses were recognized more frequent than others. The so-called respiratory viruses include respiratory syncytial virus (RSV), human metapneumovirus (hMPV),influenza virus A and B, parainfluenzae viruses, human adenoviruses, etc. However, the causative agents of a considerable proportion of respiratory specimens remain undefined by this far. Efforts in defining novel respiratory viruses, therefore, will be in great favor of praphylaxis and treatment of ARTIs.In 2005, by using a screening method for unknowm viral sequences in patient samples, Tobias Allander described a novel virus named human bocavirus (HBoV). HBoV was closely related to the bovine parvovirus (BPV) and the minute virus of canines (MVC), which had been classified in the genus Bocavirus within subfamily of Parvoviridae. HBoV was subsequently identified in Australia, Japan, Canada, France, Germany, Korea and American, indicating its global distribution. The prevalence of this newly identified virus ranged from 1.5% to 18.3%. HBoV infections appeared to more likely happen in children under 5 years old, in particular in children between 6 months to 2 years old. Further studies of the epidemiologic features of HBoV is busy doing now.In China,Hunan province reported this virus in 2006,then Zhejiang detected HBoV in the NPAs of children with LRIs,Guangzhou studied the serum epidemiology with a positive ratio of 7.06%.But,it was not enough neither the amount of the samples nor the times.ObjectiveTo describe epidemiologic features such as prevalence, age distribution and seasonality of HBoV infection and analyze clinical and molecular characteristics of HBoV infection in Chongqing, China.Methods1. Sample collection: Nasopharyngeal aspirates (NPAs) from children hospitalized for RTIs through April 2006 and March 2007 at the Children's Hospital of Chongqing Medical University.2. Direct immunofluorescence assay (DFA): NPAs were processed and airway cells were pelleted for detection of common respiratory viruses including respiratory syncytial virus (RSV), influenza virus A and B, parainfluenzae viruses1, 2 and 3, and human adenoviruses. 3. HBoV PCRs: DNA extracted from 200μl aliquot of each sample by using QIAamp ? DNA Mini Kit (QIAGEN Inc,USA), was used for the detection of HBoV NP-1 and NS1 genes.4. Epidemiological analysis: prevalence , seasonality, age distribution of HBoV infection and coinfection of HBoV and other respiratory viruses were analyzed.5. Clinical characteristics of HBoV infection: diagnosis at discharge from hospital, Clinical manifestations, laboratory findings, chest radiographic findings were reviewed and analyzed.6. Nucleotide sequence analysis and Phylogenetic analysis: HBoV NP-1 gene PCR products was confirmed by nucleotide sequence analysis and the sequences were subsequently compared with other reported HBoV sequences in the GeneBank. Phylogenetic analysis was performed using Clustal X and identity analysis of senquences of our HBoV PCR products and reference strains was done using DNAStar analyzing software.Results1. Three houndred and ninty five NPAs were collected through April 2006 to March 2007 from hospitalized children with RTIs.2. HBoV PCRs: HBoV signals were detected in 21 of the total 395 NPAs. The detedtion rate was 5.3%.The product of NP-1 gene was about 354bp and the product of NS1 was 291bp. Double positive for both NP-1 and NS1 gene PCRs were defined as HBoV positive sample.3. Among 21 children with HBoV positive results, 16 were boys and 5 were girls. The majority (20 out of 21) was under 2 years old in which 13 were younger than 1 year of age. HBoV Infections appeared to occurr nore likely in winter months. Clinical manifestations included cough, wheeze, cyanosis and various degrees of respiratory distress. The most common diagnosis was lower respiratory tract infections. Twelve out of 21 children had a course of disease longer than 10 days, in which 5 were longer than one month. Wheezing was noticed in considerable proportion of patients. Coinfection of HBoV and respiratory syncytial viruse was revealed in 3 (14.3 %) among the HBoV positive samples.4. Nucleotide sequence analysis of HBoV NP-1 gene PCR products. Ten NP-1 gene bulk PCR products were subject to nucleotide seqnence analysis. Phylogenetic analysis revealed that all of the 10 viruses were closer to HBoV ST1 than ST2 genetically. At the nucleotide level, the sequence identities of the NP-1 gene among 21 positive samples were 99.0%-100% and 98.7%-100% as compared to Swedish viruses ST1 and ST2, respectively. High identity (99.0%-100%) of the amino acid sequences was also found between 21 positive NP-1 products obtained and ST1 and ST2.ConclusionHBoV is frequently found in NPAs of hospitalized infants and children with respiratory tract diseases in Chongqing. HBoV infection appears to occur more likely in children under 2 years old and in winter. HBoV causes the respiratory disease similar to those by RSV. Wheezing and severe presentations may be related to HBoV infection. HBoV ST1 could be the dominant group circulating in Chongqing, China. Respiratory syncytial virus could coinfect with HBoV.