Age-associated aggravation of clinical disease after primary metapneumovirus infection of BALB/c mice.

Human metapneumovirus (hMPV) is associated with respiratory tract infections among children and adults. Because hMPV induces significant morbidity and mortality in the elderly, a model of hMPV infection in aged BALB/c mice was established. Young (8 weeks old) and aged (18 months old) mice were intranasally inoculated with hMPV. The infected mice showed respiratory dysfunction, as measured by plethysmography, a marked loss in weight (up to 24%), and severe histopathological abnormalities including bronchiolitis obliterans organizing pneumonia. However, clinical severity was far higher in the aged mice, and none of the young infected mice died. Although virus replication in the lung was greater in the older mice, clearance of virus was not delayed compared to young mice. Production of virus-specific antibody as well as neutralizing antibody was lower. Gamma interferon and monocyte chemotactic protein-1 levels in bronchoalveolar lavage fluid were significantly lower in older mice, whereas interleukin-6 and interleukin-4 levels were significantly higher. We observed by flow cytometry a significant increase in the CD4(+) T lymphocytes (P<0.05) of the aged mice and no difference in CD8(+) T-cell recruitment to the respiratory tract between the two groups. The present study investigated the effects of aging on the immunopathogenesis of hMPV infection and suggests that CD4(+) T lymphocytes, the cytokine response, or a defect in humoral response may be associated with the increased disease severity observed in the aged mice.

Rapid and sensitive detection of metapneumovirus in clinical specimens by indirect fluorescence assay using a monoclonal antibody.

Human metapneumovirus, with two known genotypes named A and B, is associated with mild respiratory symptoms to severe LRTI in children, high-risk adults and the elderly. Rapid and reliable methods of hMPV detection in clinical samples are essential to implement appropriate care, to better understand the pathology of hMPV and to determine its epidemiology. Respiratory samples from 1,386 patients collected during 2 consecutive years were screened for hMPV using indirect immunofluorescence (IFA) assay with a monoclonal antibody. Forty-three patients tested positive for hMPV by the IFA method. In parallel, the samples were examined with RT-PCR on the F gene. Of these, 41 specimens were RT-PCR positive. The remaining two IF positives were cultured and the cultures were subsequently RT-PCR positive. IFA showed therefore a sensitivity of 100%. No false positive signals were obtained with the influenza virus, respiratory syncytial virus or parainfluenza. When tested by RT-PCR, all IFA-negative samples (n = 204)were found negative. Therefore the specificity of IFA was 100%, IC95 [98-100%], with a negative predictive value of 100%. Based upon phylogenetic analysis of the fusion gene, both subgroups of hMPV were efficiently detected by IFA, and the viral aetiology could be given in 2 hr. These results demonstrate the potential usefulness of immunofluorescence with our monoclonal antibody for the rapid detection of hMPV in clinical specimens in the management of therapy and the control of nosocomial diffusion.