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Viruses belonging to the five species of the genus Henipavirus are distinguished on the basis of the amino acid sequences of their large protein (L). The receptor-binding protein (RBP) lacks hemagglutinating and neuraminidase activities and in the cases of Hendra virus (HeV) and Nipah virus (NiV) interacts with ephrin-B2 (EFNB2) and ephrin-B3 (EFNB3) as protein receptors. A major distinguishing feature between henipaviruses and other paramyxoviruses is the long 3′-UTRs of the N, P, F and RBP mRNAs that results in a genome that is approximately 3000 nt or longer than most of the other members of the family Paramyxoviridae. The unedited P mRNA encodes phosphoprotein (P) protein. The edited P mRNA encodes a zinc-binding cysteine-rich protein (V) with the exception of Cedar virus which does not appear to co-trancriptionally edit transcripts from the P/C gene. There is a 3-nt intergenic sequence (CUU) at each gene junction. All members encode a non-structural protein (C). The viruses in this genus (with the possible exception of Mòjiāng virus [MojV]) are found in bats. Hendra and Nipah viruses have been associated with limited outbreaks with high lethality in domesticated animals and humans. Different from most paramyxoviruses, henipaviruses have a wide host range, including bats, pigs, horses and humans. The identification of the highly conserved EFNB2 as the main functional receptor for both HeV and NiV and the widespread occurrence of this molecule in vertebrates, particularly in arterial, but not venous, endothelial cells, in the smooth muscle of the tunica media and in neurons, provide an explanation for the wide host range of henipaviruses and the systemic nature of the infections they cause.
See discussion under family description.
HeV and NiV cross-neutralize and have considerable sequence relatedness but can also be distinguished on either basis.
HeV has been detected exclusively in Australian flying foxes whereas NiV or cross-reacting anti-NiV antibodies have been detected in fruit bats from Indonesia, Malaysia, Thailand, Cambodia, India, Bangladesh and Madagascar. Moreover, Ghana virus RNA and Nipah- and Hendra-cross reactive antibodies have been detected in a number of countries in Sub-Saharan Africa.
Species demarcation is now entirely based on the distance in the phylogenic tree based on the comparison of complete L protein amino acid sequences. Since the primary criterion is the tree topology, whether or not a virus belongs to the same species becomes a matter of branch length between the nearest node and the tip of the branch. This length is defined as 0.03 in the trees generated as described in the legend to Figure 3.Paramyxoviridae. HeV and NiV are also distinct both antigenically and by geographic distribution.
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