Nipah virus, an emerging zoonotic disease causing fatal encephalitis

Abstract

Nipah virus is an acute febrile illness that can cause fatal encephalitis. It is an emerging zoonotic paramyxovirus endemic to south-east Asia and the western Pacific, and can be transmitted by its primary reservoir of fruit bats, through intermediate animal vectors and by human-to-human spread. Outbreaks of Nipah virus encephalitis have occurred in Malaysia, Singapore, Philippines, India and Bangladesh, with the most recent outbreak occurring in Kerala, India in late 2021. Extremely high case fatality rates have been reported from these outbreaks, and to date no vaccines or therapeutic management options are available. Combining this with its propensity to present non-specifically, Nipah virus encephalitis presents a challenging diagnosis that should not be missed in patients returning from endemic regions. Raising awareness of the epidemiology, clinical presentation and risk factors of contracting Nipah virus is vital to recognise and manage potential outbreaks of this disease in the UK.

Keywords: Nipah virus; emerging diseases; encephalitis; tropical medicine; zoonotic disease.

Fig 1.

(a) Areas where there is risk of Nipah virus transmission. (b) Nipah virus' reservoir host, the Pteropus bat, pictured in a public park in Rajasthan, India (Photo courtesy of Jakub Halun) and reproduced under a CC BY-SA 4.0 licence.

Fig 2.

Possible routes for disease transmission of Nipah virus encephalitis.

Fig 3.

(a) MRI FLAIR imaging illustrating multiple small hyperintensities with cortical involvement. (b) MRI DWI illustrating multiple bilateral hyperintensities. Reproduced with permission from Anam et al.

Fig 4.

Bubble plot illustrating mortality rates throughout the Nipah virus outbreaks from 1999 to 2021.