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Henipavirus is a genus of negative-strand RNA viruses in the family Paramyxoviridae, order Mononegavirales containing five established species, and numerous others still under study. Henipaviruses are naturally harboured by several species of small mammals, notably Pteropus (flying foxes), microbats of several species, and . Henipaviruses are characterised by long and a wide host range. Their recent emergence as zoonosis pathogens capable of causing illness and death in and humans is a cause of concern.
In 2009, RNA sequences of three novel viruses in phylogenetic relationship to known henipaviruses were detected in African straw-colored fruit bats ( Eidolon helvum) in Ghana. The finding of these novel henipaviruses outside Australia and Asia indicates that the region of potential endemicity of henipaviruses may be worldwide. These African henipaviruses are slowly being characterised.
Nipah virus and Hendra virus are both considered category C (USDA-HHS overlap) .
Embedded within the lipid membrane are spikes of F (fusion) protein trimers and G (attachment) protein tetramers. The function of the G protein (except in the case of MojV-G) is to attach the virus to the surface of a host cell via Ephrin B1, B2, or B3, a family of highly conserved mammalian proteins. The structure of the attachment glycoprotein has been determined by X-ray crystallography. The F protein fuses the viral membrane with the host cell membrane, releasing the virion contents into the cell. It also causes infected cells to fuse with neighbouring cells to form large, multinucleated syncytia.
In common with other members of the Paramyxoviridae family, the number of in the henipavirus genome is a multiple of six, consistent with what is known as the 'rule of six'. Deviation from the rule of six, through mutation or incomplete genome synthesis, leads to inefficient viral replication, probably due to structural constraints imposed by the binding between the RNA and the N protein.
Three additional protein products are produced from the henipavirus P gene: V, W, and C. The V and W proteins are generated through an unusual process called RNA editing. This specific process in henipaviruses involves the insertion of extra guanosine residues into the P gene mRNA prior to translation. The addition of a single guanosine results in production of V, and the addition of two guanosines residues produces W. The C protein is not produced through RNA editing but instead by leaky scanning of the host cell ribosome during translation of viral mRNA. P, V, and W possess an alternate open reading frame which results in production of C. P, V, W, and C are known to disrupt the host innate antiviral immune response through several different mechanisms. P, V, and W contain STAT1 binding domains, and act as interferon antagonists by sequestering STAT1 in the nucleus and cytoplasm. The C protein controls the early pro-inflammatory response and is also known to promote the viral budding process via a ESCRT-dependent pathway.
The primary mechanism of protection against NiV and HeV induced by vaccination is thought to be neutralizing antibodies. However, a number of preclinical vaccine studies in animal models of disease have identified that the cell-mediated immune response including CD8+ and CD4+ T-cells may play a role in protection.
There is evidence that habitat loss for flying foxes, both in South Asia and Australia (particularly along the east coast) as well as encroachment of human dwellings and agriculture into the remaining habitats, is creating greater overlap of human and flying fox distributions.
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