Objectives:

Recently a novel paramyxovirus isolated from children with respiratory tract disease was identified that was named human metapneumovirus (hMPV) and classified as a member of the metapneumovirus genus. We investigated the impact of hMPV infections and developed new tools and reagents for applied and fundamental research.

Methods:

A large collection of hMPV isolates was generated, originating from different geographical locations from 1980 onwards. Sequence analyses were performed to study the genetic diversity of hMPV. Antigenic variation was measured with postinfection animal sera. A reverse genetics system was developed to produce recombinant hMPV. Improved diagnostic tests for hMPV were designed.

Results:

Retrospective studies revealed that approximately 7% of the samples collected from individuals suffering from respiratory tract disease where positive for hMPV. HMPV was detected primarily in very young children and immunocompromised individuals and mostly in January and February. Clinical symptoms associated with hMPV infection in young children were found to be similar to those observed for RSV infections. In the 2000 and 2001 winter seasons in the Netherlands, only RSV was found to be associated with respiratory tract illnesses more frequently in an academic hospital setting. Sequence information on the fusion and attachment surface glycoproteins revealed that there are two main genetic lineages of hMPV (A and B) each of which, can be separated in two sublineages (A1, A2, B1 and B2). Virus neutralization experiments using animal sera indicated that the two main lineages represent different hMPV serotypes. We have sequenced the full-length genome of prototype strains representing each of these four genetic lineages. For both serotypes a prototype virus isolate was selected for which minigenome reporter systems were made and subsequently infectious recombinant hMPVs were rescued. We also developed and evaluated new diagnostic assays for detection of hMPV strains from all genetic lineages with equal specificity and sensitivity.

Conclusions:

hMPV is an important viral pathogen. Young children, immunocompromised individuals and frail elderly are at risk for serious hMPV-associated disease. The genetic and antigenic heterogeneity of hMPV isolates should be taken into account for the development of diagnostic tests and evaluation of future vaccines. The applied and fundamental research on hMPV will benefit from the newly developed tools and reagents.