Orthomyxoviridae

Class V viruses. The genome consists of a single negative strand of RNA that is present as several separate segments each of which acts as a template for a single mRNA. The nucleocapsid is helical and has a viral-specific RNA polymerase for the synthesis of the mRNAs. They leave cells by budding out of the plasma membrane and are thus enveloped. They usually have two classes of spike protein in the envelope. One has haemagglutinin activity and the other acts as a neuraminidase and both are important in the invasion of cells by the virus. The major viruses of this group are the influenza viruses.