[Human Metapneumovirus Infection]

Human metapneumovirus (HMPV) was first isolated in 2001 from young children with symptoms of acute respiratory infections. Studies revealed that HMPV has circulated worldwide for more than 50 years in hu- man populations. HMPV is classified into two major, distinct groups, A and B, which show antigenic differ- ences, but clinical symptoms of infection with these groups are indistinguishable. The symptoms are often severe and similar to those of respiratory syncytial virus infections. HMPV is detected in more than 10% of children under five years old suffering from acute respiratory infections. Elderly people are also affected with HMPV and may develop severe respiratory diseases. Recently, point-of-care testing based on immu- nochromatography became available in Japan under the coverage of medical insurance, further revealing clini- cal pictures of HMPV infections and improving clinical treatment and control measures. Sensitive nucleo- tide amplification techniques are also available for the detection of HMPV. However, the virus titers and amounts of viral antigens decline significantly after 5 days of illness. Therefore, laboratory testing to detect HMPV antigens or genomes should be conducted using clinical specimens before 4 days of illness. Assays to detect immunoglobulin specific to HMPV (ELISA and neutralizing assay) have also been established, alt- hough they have not yet been approved as extracorporeal diagnostic medicines. [Review].