Human bocavirus (HBoV), a newly cloned human virus of the genus Bocavirus, was detected by PCR from nasopharyngeal swab samples (8 of 318; 5.7%) collected from children with lower respiratory tract infections. HBoV may be one of the causative agents of lower respiratory tract infections in young children.The family Parvoviridae contains two subfamilies: Parvovirinae, which infects vertebrates, and Densovirinae, which infects insects. The subfamily Parvovirinae consists of five genera: Parvovirus, Erythrovirus, Dependovirus, Amdovirus, and Bocavirus (12). Parvovirus B19, which belongs to the genus Erythrovirus, is a well-known human pathogen (3,12). A new human virus of the genus Bocavirus, provisionally named human bocavirus (HBoV), was recently cloned from pooled human respiratory tract samples and is considered to be pathogenic to humans (1). In this study, nasopharyngeal swab samples obtained from children with lower respiratory tract infections were investigated for the presence of HBoV.

Human metapneumovirus (HMPV) is a major causative agent of severe bronchiolitis and pneumonia. Its fusion (F) protein must be cleaved by host proteases to cause membrane fusion, a critical step for virus infection. By generating Vero cells constitutively expressing the transmembrane serine protease TMPRSS2 and green fluorescent protein-expressing recombinant HMPV, we show that TMPRSS2, which is expressed in the human lung epithelium, cleaves the HMPV F protein efficiently and supports HMPV multiplication. The results indicate that TMPRSS2 is a possible candidate protease involved in the development of lower respiratory tract illness in HMPV-infected patients.

Human metapneumovirus (hMPV) has been recently discovered as an etiological agent of acute respiratory infections. Our purpose was to asses the virological and clinical features of children with respiratory infections caused by hMPV. We examined 658 nasopharyngeal swab samples obtained from 637 children with respiratory infections for hMPV by using reverse transcription-PCR (RT-PCR). A total of 268 samples from 637 children were inoculated onto tertiary monkey kidney cells. A total of 36 serum samples (26 in the acute phase and 10 in the convalescent phase) from the 26 hMPV-positive children were tested for immunoglobulin G (IgG) and IgM antibodies to hMPV by using an indirect immunofluorescence assay. We detected hMPV in 57 (8.9%) of the 637 samples by using RT-PCR and isolated 7 (2.6%) hMPV strains of the 268 samples in cell cultures. A total of 12 (46.2%) of 26 hMPV-positive children were suspected to have primary infection with hMPV as determined by an indirect immunofluorescence assay. The infected children were diagnosed as having wheezy bronchitis (36.8%), upper respiratory tract infection (26.3%), bronchitis (22.8%), and pneumonia (14.0%). We showed that two hMPV groups were circulating in different regions during the same period and that reinfection with hMPV frequently occurs in childhood. The RT-PCR test is the most sensitive test for detection of hMPV, and a serological test may be useful to differentiate between primary infection and reinfection with hMPV.

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus and an aetiological agent of infectious mononucleosis, has a unique tropism for B lymphocytes. Clinical and laboratory features of chronic active EBV infections are chronic or persistent infectious mononucleosis-like symptoms and high antibody titre against early antigens (EA). Kawasaki disease (KD), aetiology unknown, is thought to be self-limited immunologically mediated vasculitis. Clinical features of KD are fever, rash, mucositis, lymphadenopathy and coronary artery damage. We report here a child with chronic active EBV infection accompanied by dilatation of coronary arteries. All the EBV-determined nuclear antigen (EBNA)-positive lymphocytes had exclusively CD4 antigen, as revealed by dual staining immunofluorescence analysis. Southern blot hybridization showed that the purified CD4+ cells harboured EBV genome.

A new human pneumovirus, provisionally designated human metapneumovirus, was discovered by Dutch researchers. We examined 142 serum samples from the general population aged from 1 month to 35 years in Japan for human metapneumovirus antibody by indirect immunofluorescence assays using human metapneumovirus-infected monkey kidney cells. The overall prevalence of human metapneumovirus infection was 72.5%. The seropositive rate was lowest in the age group of 6 months to 1 year and gradually increased with age. All of the children had been exposed to human metapneumovirus by the age of 10 years. The results show that human metapneumovirus is circulating in the Japanese population and is a ubiquitous virus acquired early in life.

A new human virus, provisionally named human bocavirus (HBoV), was discovered by Swedish researchers in 2005. A new immunofluorescence assay using Trichoplusia ni insect cells infected with a recombinant baculovirus expressing the VP1 protein of HBoV was developed, and the levels of immunoglobulin G antibody to the VP1 protein of HBoV in serum samples were measured. The overall seroprevalence rate of antibodies against the VP1 protein of HBoV in a Japanese population aged from 0 months to 41 years was 71.1% (145 of 204). The seropositive rate was lowest in the age group of 6 to 8 months and gradually increased with age. All of the children had been exposed to HBoV by the age of 6 years. A rise in titers of antibody against the VP1 protein of HBoV during the convalescent phase was observed for four patients with lower respiratory tract infections, and HBoV DNA was detected in nasopharyngeal swab and serum samples from all four patients. These results suggest that HBoV is a ubiquitous virus acquired early in life and that HBoV might play a role in the course of lower respiratory tract infections.

HCoV-NL63, the fourth human coronavirus, has been isolated recently from children with respiratory tract infections, including upper respiratory infection, bronchiolitis, and pneumonia. The virus has been also detected in immunocompromised adults with respiratory tract infections. A total of 118 nasopharyngeal swab samples from 118 hospitalized young children aged less than 2 years with bronchiolitis who were not infected with human respiratory syncytial virus, influenza A or B, or human metaneumovirus were selected. Three (2.5%) of the 118 samples were positive for HCoV-NL63 by reverse transcription-polymerase chain reaction tests. HCoV-NL63 may be one of the causative agents of bronchiolitis in young children.

Complete genes encoding the predicted nucleoprotein (N), phosphoprotein (P), matrix protein (M), fusion protein (F), M2-1protein, M2-2protein, small hydrophobic protein (SH), and attachmentprotein (G) of seven newly isolated human metapneumoviruses (hMPVs) were analyzed and compared with previously published data for hMPV genes. Phylogenetic analysis of the nucleotide sequences indicated that there were two genetic groups, tentatively named groups 1 and 2, similar to the grouping of human respiratory syncytial virus. Although the predicted amino acid sequences of N, P, M, F, and M2 were highly conserved between the two groups (amino acid identities, 96% for N, 85% for P, 97% for M, 94% for F, 95% for M2-1, and 90% for M2-2), the amino acid identities of the SH and G proteins were low (SH, 58%; G, 33%). Furthermore, each group could be subdivided into two subgroups by phylogenetic analysis, tentatively named subgroups 1A and 1B and subgroups 2A and 2B. The predicted amino acid sequences of G within members of each subgroup were highly conserved (amino acid identities, 88% for group 1A, 93% for group 1B, and 96% for group 2B). The G of hMPV is thought to be the major antigenic determinant and to play an important role in the production of neutralizing antibodies. Clarification of the antigenic diversity of G is important for epidemiological analysis and for establishment of strategies to prevent hMPV infection.