Pneumoviridae

Structure Pneumoviruses are pleomorphic, capable of producing spherical and filamentous, enveloped virions (virus particles) that vary in size from 150 to 200 nm in diameter. The nucleocapsid consisting of a protein shell and viral nucleic acids has a helical symmetry. Nucleocapsids have a diameter of 13.5 nm and a helical pitch of 6.5 nm. Genome The genome is composed of negative-sense, single-stranded RNA that is non-segmented. It is about 15 kbp in size, and encodes eleven proteins. Viruses in this family are often associated with respiratory infections, and are transmitted through respiratory secretions. P – Phosphoprotein required for replication. M1 – Matrix protein. Facilitates nucleocapsid and envelope interactions. M2-1 – Matrix protein. Intragenic and intergenic transcription factor required for mRNA transcript elongation. M2-2 – Matrix protein. Involved in regulating transcription and replication. When over expressed, has been shown to inhibit viral replication. F – Fusion protein. Type I glycoprotein that facilitates fusion between the virus and the host cell membrane. SH – Small hydrophobic protein. Non essential. Exact function is unknown. Suggested to alter membrane permeability and block apoptosis. G – Type II glycoprotein. L – RNA dependent RNA polymerase. Required for replication. Once sufficient P, N, L, and M2 proteins are available to create a capsid around the newly replicated genome, the virus undergoes replication. After replication, the P, L, and M proteins participate in forming the ribonucleocapsid. Once virion assembly is complete, the virion egresses by budding out of the cell. == Infection in humans ==

Human metapneumovirus (HMPV) was first classified as a pneumovirus in 2001. It is a negative-strand RNA virus that is the second most common cause of lower respiratory infection in young children. Pneumoviruses are intermediate in size between viruses of the families Paramyxoviridae and Orthomyxoviridae. Cytoplasmic inclusions are considerably denser than those of other viruses in the family. Human metapneumovirus infection is very similar to the common cold but can be serious enough to cause influenza-like illness. It will typically occur in the winter and early spring. This specific infection is most common in children, especially under the age of five. Common signs and symptoms include a runny nose, nasal congestion, sore throat, cough, headache, body aches, and fever, which can be seen in many other viral respiratory infections. More severe signs and symptoms may include chest pain, wheezing due to inflammation and tightening of the small airways in the lungs, shortness of breath, dizziness, severe fatigue, dehydration, pneumonia, or a persistent fever. It typically resolves within a week. If seen in the elderly there is cause for concern, as it can develop into pneumonia. == Taxonomy ==