Detection of human bocaviruses 1 to 4 from nasopharyngeal swab samples collected from patients with respiratory tract infections.

Human bocaviruses (HBoV) 1, 2, 3, and 4 (HBoV1-4) were detected in 132 (15.5%), 5 (0.6%), 3 (0.4%), and 5 (0.6%) of 850 nasopharyngeal swab samples collected from children with respiratory tract infections, respectively. Out of the 145 HBoV1-4-positive samples, 62 (42.8%) were codetected with other respiratory viruses.

Detection of KI polyomavirus and WU polyomavirus DNA by real-time polymerase chain reaction in nasopharyngeal swabs and in normal lung and lung adenocarcinoma tissues.

Polyomaviruses KI (KIPyV) and WU (WUPyV) were detected from 7 (3.0%) and 38 (16.4%) of 232 children with respiratory tract infections by real-time PCR. The rates of infection by KIPyV and WUPyV alone were 3 of 7 (42.9%) and 20 of 38 (52.6%), respectively. In the other samples, various viruses (human respiratory syncytial virus, human metapneumovirus, human rhinovirus, parainfluenza virus 1 and human bocavirus) were detected simultaneously. One case was positive for KIPyV, WUPyV and hMPV. There was no obvious difference in clinical symptoms between KIPyV-positive and WUPyV-positive patients with or without coinfection. KIPyV was detected in one of 30 specimens of lung tissue (3.3%). Neither of the viruses was detected in 30 samples of lung adenocarcinoma tissue.

Antibodies against structural and nonstructural proteins of human bocavirus in human sera.

Immunofluorescence assays (IFAs) for detection of human bocavirus (HBoV) proteins (VP1, VP2, NP-1, and NS1) were developed. The VP1 IFA was the most sensitive for detection of IgG antibody and suitable for screening. IgG antibodies in convalescent-phase sera from HBoV-positive patients were detected by VP1 and VP2 IFAs. Sensitivities of NP-1 and NS1 IFAs were low.

Detection of four genetic subgroup-specific antibodies to human metapneumovirus attachment (G) protein in human serum.

Human metapneumovirus (hMPV) strains are classified into two genetic groups, A and B, each of which is further divided in two genetic subgroups, A1, A2, B1 and B2. hMPV encodes two major surface glycoproteins, the fusion (F) and attachment (G) proteins, which may be immunogenic and protective antigens. Although the amino acid sequences of hMPV F protein are highly conserved, those of the G protein are highly variable with low amino acid identity between the two groups. To address the antigenic variation between the genetic subgroups, we developed an immunofluorescence assay (IFA) method using Trichoplusia ni (Tn5) insect cells infected with each recombinant baculovirus-expressed hMPV G (Bac-G) protein of the four genetic subgroups. The titre of each antibody to the four Bac-G proteins was measured by the IFA in 12 paired serum samples obtained from children infected with hMPV of each genetic subgroup. Although 11 of the 12 acute-phase serum samples in paired samples were negative for the antibody to any Bac-G proteins, all of the convalescent-phase serum samples in those paired samples were positive for the antibody to only one of the four Bac-G proteins of the infecting genotype of hMPV. Since the antibody response to hMPV G protein was transient and genetic subgroup-specific without cross-reactivity, four genetic subgroups on the basis of hMPV G protein could be identified as different serotypes. This assay may be useful for the study of immune responses of humans to different hMPV strains, especially for clarifying the risk of reinfection with hMPV.

Seroepidemiology of human bocavirus in Hokkaido prefecture, Japan.

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.