No abstract

Background: Four human coronaviruses are currently known to infect the respiratory tract: human coronaviruses OC43 (HCoV-OC43) and 229E (HCoV-229E), SARS associated coronavirus (SARS-CoV) and the recently identified human coronavirus NL63 (HCoV-NL63). In this study we explored the incidence of HCoV-NL63 infection in children diagnosed with respiratory tract infections in Belgium.

Human respiratory syncytial virus (HRSV) is an enveloped virus with a nonsegmented negative-strand RNA genome (family Paramyxoviridae, genus Pneumovirus). HRSV is the major cause of acute lower respiratory tract infections in infants and young children. It is also recognized as an important pathogen in immunocompromised patients and the elderly (12, 58, 65). Two major subgroups of HRSV (HRSV-A and HRSV-B) have been described based on antigenic and sequencing studies (2,6,9,25,34). An unusual feature of HRSV is that repeated infections with both subgroups can occur, despite the development of mucosal and systemic immune responses (18,19,20). Although HRSV-A and -B strains can cocirculate, subgroup A is dominant in more epidemics (1,21,23,33). Several genotypes can cocirculate in a single epidemic season, and different genotypes can predominate in consecutive epidemics (3,7,21,42). In addition, viruses isolated in geographically distant places and in different years may be more closely related than viruses isolated in the same place during the same season (5, 14, 32).The attachment G glycoprotein is a type II integral membrane protein (56, 64) that shows the highest degree of diversity both between and within the two HRSV subgroups (25, 54). The G glycoprotein is one of the main antigens responsible for inducing a neutralizing immune response (11). It is highly glycosylated, and the majority of the potential glycosylation sites are clustered in two mucin-like variable regions of the ectodomain separated by a highly conserved 13-amino-acid motif, which is considered to be the putative site for virus attachment to the cell receptor (8,25,54).Three types of epitopes have been identified in the G molecule: (i) conserved epitopes, shared by subgroups A and B (2, 34), (ii) subgroup-specific epitopes, and (iii) strain-specific or variable epitopes (2, 16). The strain-specific epitopes have been mapped within the hypervariable C-terminal third of the G glycoprotein ectodomain, and there is evidence of progressive accumulation of genetic and antigenic changes in this region (6,14,50).The epidemiology and the possible mechanisms by which HRSV can evade the immune response are still not completely elucidated. The significance of genetic drift and nonprogressive random variation in the molecular evolution of HRSV is a question that remains to be answered. No studies have been conducted on sequence data over more than 10 consecutive HRSV epidemics, and most reports are based on sequencing of only a limited region of the G glycoprotein (41,45,62). In order to investigate the tempo and the mode by which HRSV-A evolves, we sequenced 629 bp of the G glycoprotein ectodomain from 112 subgroup A strains obtained during 19 consecutive years in Belgium (1984Belgium ( to 2002. In the present work, we confirm five previously described amino acid sites and report eight novel sites in the G glycoprotein to be under positive selection. These results suggest that HRSV-A strains are evolving under selective pressure operating in certain codo...