The paramyxoviruses (Paramyxoviridae family) are membrane enveloped, singled-stranded, negative-sense RNA viruses. They are classified into 7 genera belonging to two subfamilies. Until the turn of the new millennia, Respirovirus, Morbillivirus, and Rubulavirus were the three main genera that comprise the Paramyxovirinae subfamily. They generally contain three structural and three non-structural genes. Two structural proteins, the fusion and attachment envelope glycoproteins, are required for virus entry and fusion. Hendra and Nipah viruses have the same gene organization but have substantially longer genomes (~18 kb vs <15 kb) and sequence divergence to merit classification into a new genus named Henipavirus. The designation of a new Henipavirus genus also led to a re-classification of a group of avian paramyxoviruses into their own Avulavirus genus (they were formerly part of the Rubulavirus genus). Presently, 5 distinct genera comprise the Paramyxovirinae subfamily. Metapneumovirus and Pneumovirus are more distantly related, have several additional non-structural genes, and form a separate Pneumovirinae subfamily. In addition, while both subfamilies have fusion and attachment proteins, the Pneumovirinae do not appear to require the attachment protein for virus entry and replication. Thus, we will restrict our review on henipavirus entry to comparisons with other members of the Paramyxovirinae subfamily.
The majority of paramyxoviruses cause some sort of respiratory disease although henipaviruses can cause severe encephalitis in addition, while morbilliviruses (Measles in humans, Canine Distemper Virus in dogs, Rinderpest virus in cattle/swine) can cause immunosuppression, CNS disease, and gasteroenteritis. Respiroviruses (Human parainfluenza 1, 3) and Rubulaviruses (HPIV2, 4 and Mumps virus) can cause significant morbidity in pediatric populations. Mumps is a well-known childhood disease that can lead to swelling of the salivary glands and testicles, and can even proceed to frank meningitis in susceptible unvaccinated individuals. Epidemics of Newcastle disease virus and other virulent strains of avian paramyxoviruses (Avulavirus) can have a significant economic impact in the poultry industry.
(This introduction is abstracted from Benhur Lee et al. "Modes of Paramyxovirus Fusion: a Henipavirus perspective" Trends in Microbiology, August 2011, Vol 19, No.8, p389-399)