| Objective:The high detection rate of human bocavirus（HBo V）is believed to be closely related to acute respiratory tract infections.This study focused on patients with acute respiratory tract infections in Qingdao City,monitored major viral pathogens,and established the viral and bacterial pathogen spectrum of HBo V-infected patients to explore their specific clinical features.A comprehensive understanding of the epidemiological and genetic characteristics of HBo V respiratory infections in Qingdao City will provide baseline data and a scientific basis for the prevention and control of HBo V-related respiratory infections,clinical diagnosis and treatment,molecular epidemiology research,as well as the prevention and treatment of acute respiratory tract infections.Methods:This study collected 2,340 respiratory specimens from patients with acute respiratory tract infections at the West Coast Campus of Qingdao University Affiliated Hospital and Laoshan Campus of Qingdao University Affiliated Hospital between January2018 and December 2019.Viral pathogen detection was performed using multiplex real-time fluorescence polymerase chain reaction（RT-PCR）.Bacterial pathogen detection was performed on HBo V-positive specimens using the same RT-PCR method.Epidemiological characteristics and related clinical manifestations of HBo V were analyzed in conjunction with the patients’demographic data and clinical information.Nested PCR was used to amplify and sequence the VP1/VP2 gene fragment of HBo V-positive samples,followed by nucleotide sequencing analysis,phylogenetic analysis,selection pressure analysis,and molecular evolution analysis using bioinformatics methods.Results:Epidemiological characteristics and clinical manifestations analysis:（1）Out of2,340 respiratory specimens,138 were HBo V-positive with a male-to-female ratio of 1.8:1.The HBo V detection rates for different age groups were<2 years-27.54%,2-4 years-21.01%,5-14 years-15.22%,15-64 years-21.01%,and≥65 years-15.22%.（2）HBo V was detected only during specific months in 2018 and 2019.（3）Out of 138 HBo V-positive specimens,106 cases（76.81%）had HBo V as the only detected viral pathogen,while 32cases（23.19%）had co-infections with one or two other viruses.（4）Bacterial pathogens were detected in 103（74.6%）HBo V specimens,with co-infections ranging from one to four bacterial pathogens.（5）The most common symptoms of respiratory infection in HBo V-infected patients were cough and fever.（6）Differences in neutrophil,adenosine deaminase,creatine kinase,cystatin,and bicarbonate levels were statistically significant（P<0.05）between the single HBo V infection group and the mixed HBo V infection group.（7）Differences in red blood cell count and triglyceride levels were statistically significant（P<0.05）between HBo V patients with and without bacterial pathogen infections.（8）The only statistically significant difference（P<0.05）between HBo V patients with and without Pseudomonas aeruginosa infections was in blood sodium levels.Genetic characteristics analysis results:（1）Phylogenetic analysis showed that all HBo V clinical isolates in this study were HBo V1 with a close genetic distance between the isolates.（2）Homology analysis of the HBo V VP1/VP2 gene fragment revealed that compared to the prototype strain,the nucleotide and amino acid homology of the clinical isolates in this study were 97.78%-100.00%and 95.00%-100.00%,respectively.Compared to foreign HBo V1 representative strains,the nucleotide and amino acid homologies were97.78%-100.00%and 94.97%-100.00%,respectively.（3）Amino acid mutation analysis showed that 11 nucleotide mutation sites were found in the HBo V clinical isolates in this study,resulting in the mutation of four amino acids.（4）Selection pressure analysis revealed that the HBo V clinical isolates in this study had multiple negative selection sites and only one positive selection site.（5）Bayesian evolutionary analysis results showed that the average evolutionary rate of the HBo V VP1/VP2 gene fragment was 7.657×10-4substitutions/site/year,indicating a relatively low evolutionary rate.Conclusions:1.HBo V1 was identified as the primary pathogen in this study for HBo V infections.2.The potential effects of HBo V infection on the body need further study.3.The clinical isolates analyzed in this study show high homology with prevalent reference strains,with limited genetic variation.4.Despite negative selection pressure,a small amount of positive selection pressure was observed in HBo V,emphasizing the need for continuous monitoring. |
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