myxovirus

myxovirus, any of a group of viruses known for their ability to react with mucin, the main structural component of mucus occurring on the surface of host cells (hence, the prefix myxo-, Greek for “mucin”).

Myxoviruses possess a surface protein known as hemagglutinin, which helps the virus particles navigate and bind to mucin. They also possess neuraminidase, an enzyme that breaks bonds within mucin, thereby reducing the viscosity of the mucus barrier and allowing virus particles to penetrate cells and initiate infection. Binding to mucin also causes hemagglutination, in which red blood cells clump together (agglutinate); this phenomenon serves a role in diagnostics, facilitating the detection of the virus. The myxovirus particle itself is enveloped in a fatty membrane and is variable in shape, from spheroidal to filamentous, and in size, from 60 to 300 nm (nanometer; 1 nanometer = 10^-9 meter) in its longest dimension. The particle further is studded with spikelike protein projections and contains single-stranded ribonucleic acid (RNA).

Myxoviruses make up two families, Orthomyxoviridae and Paramyxoviridae. Among the myxovirues of Orthomyxoviridae are the influenza viruses, while Paramyxoviridae includes myxoviruses that cause the common cold, mumps, and measles in humans; canine distemper in dogs; rinderpest in cattle; and Newcastle disease in fowl. Orthomyxoviruses and paramyxoviruses differ in their genomic structure. Orthomyxoviruses have a segmented genome, meaning the genetic material is divided into distinct pieces, or segments, each usually encoding one or two proteins. Paramyxoviruses, on the other hand, have a nonsegmented genome, made up of a single, continuous, linear, negative-sense RNA molecule.