Aetiology
Nipah virus (NiV) and Hendra virus (HeV) are both single-stranded RNA viruses in the genus Henipavirus, within the family Paramyxoviridae.[17] The natural reservoir for the viruses are fruit bats of the genus Pteropus, in whom they do not cause disease.[18] The viruses are transmitted from these bats to intermediate hosts, predominantly pigs and/or horses, who develop disease.
Transmission to humans may occur via several routes:
Contact with bats or their secretions (e.g., consumption of date palm sap contaminated by bat saliva and urine).[19][20][21] This has been well reported for NiV in Bangladesh and Indian outbreaks, but has not been reported in HeV.[20][13]
Contact with sick intermediate hosts, most likely via urine or oronasal secretions.[17] This has been reported for both NiV and HeV. For NiV outbreaks, pigs were the main intermediate host.[22][23] For HeV, contact with horses is the predominant factor.[13]
Human-to-human transmission.[19][24][25][26] This has been well reported for NiV, particularly in Bangladesh outbreaks.[24] However, human-to-human transmission has not been observed with HeV.[13]
Pathophysiology
Due to the relative paucity of cases, the pathophysiology of henipavirus infections is not well established; however, common pathological features include vasculitis (with micro-infarctions and thromboses), as well as direct parenchymal infection.
These features are particularly seen in the central nervous system, but also occur in other organs, including the lungs.[17][27] The balance between pathogen- and host-related factors is not presently known. Both viruses are able to cause relapsed encephalitis, but the pathophysiological mechanism underlying this is not yet clear.[17][Figure caption and citation for the preceding image starts]: Photomicrograph showing formation of a thrombus and degenerative breakdown of the endothelial layer caused by NiV infectionCDC/Brian W.J. Mahy, BSc, MA, PhD, ScD, DSc [Citation ends].
[Figure caption and citation for the preceding image starts]: Photomicrograph showing some of the pathological changes associated with NiV infection affecting the central nervous systemCDC/Brian W.J. Mahy, BSc, MA, PhD, ScD, DSc [Citation ends].
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