Nipah virus: epidemiology, outbreaks and guidance
Source: gov.uk (2025-05-27)

The epidemiology, symptoms, diagnosis and management of Nipah virus infections.

Background

Nipah virus (NiV) infection is a zoonotic virus (in other words, it can be transmitted from animals to humans). It can also be transmitted through contaminated food or directly from human-to-human. NiV is a member of the family Paramyxoviridae, genus Henipavirus. The natural reservoir of NiV is bats, particularly fruit bats of the Pteropus genus.

Epidemiology

NiV was initially isolated and identified in 1999 during an outbreak of encephalitis and respiratory illness among pig farmers and people with close contact with pigs in Malaysia and Singapore.

Outbreaks have occurred subsequently in parts of Northeast India and almost annually since 2001 in specific districts in Bangladesh. More recently, cases have been reported in Kerala in Southern India following its first outbreak of NiV infection in 2018. Cases of Henipavirus infection have also occurred in the Philippines, believed to have been caused by NiV or a Nipah-like virus.

NiV has been isolated from the urine of bats in Malaysia, and antibodies against NiV have been detected in 23 species of bat across Asia, Ghana and Madagascar. However, human outbreaks of NiV infection have not been identified outside South and South East Asia, and most outbreaks have occurred in rural or semi-rural locations.

Figure 1. Map of human cases of NiV including specific subregions in the affected country

(See the HCID: country specific risk webpage (https://www.gov.uk/guidance/high-consequence-infectious-disease-country-specific-risk) for further information on human cases.)

Transmission

The 1998 Malaysian outbreak occurred following a spill-over event. NiV from bats spread to pigs, followed by transmission to humans exposed to the infected urine and/or respiratory secretions of infected pigs. Other outbreaks have been associated with consumption or collection of foodstuffs, such as raw or partially fermented date palm sap, which were contaminated with bat saliva and/or excreta containing NiV.

Human-to-human transmission of NiV in Bangladesh and India has been reported previously. This is most commonly seen in the family and close contacts of NiV infected cases. Close and direct, unprotected contact with infected patients, especially those with respiratory symptoms, has been implicated as a transmission risk.

NiV ribonucleic acid (RNA) has been detected in semen from an individual who received treatment for NiV infection, with RNA detected at day 26 following onset of illness (but not at days 42 or 59). These findings suggest that there may be a potential risk of sexual transmission of NiV, although the viability of NiV detected in the individual’s semen remains unknown, and sexual transmission of NiV has not been described to date.

There is evidence that NiV can infect other animals, including dogs, cats, goats, horses and sheep.

Symptoms

The most important complication of NiV infection is encephalitis, which is associated with a high mortality rate; however, the full spectrum of clinical illness is not completely understood. The incubation period is presumed to be 4 to 21 days, however longer incubation periods have rarely been observed in previous outbreaks.

Typically, patients present with a sudden onset, non-specific flu-like or febrile illness. Pneumonia and other respiratory manifestations have also been described as a feature, but their onset appears to be variable. Encephalitis or meningitis are a key hallmark of NiV infection, with associated symptoms usually developing after 3 to 21 days from illness onset. Cerebrospinal fluid abnormalities are similar to those seen in other acute viral central nervous system infections.

NiV case fatality rates have varied between outbreaks and appear to be related to the strain of infection, but it is high overall (40 to 75%). Neurological sequelae may occur in survivors, including persistent seizures and personality changes. Encephalitis due to relapse or reactivation of virus have been reported months and years after initial exposures.

Diagnosis

Any suspected cases in England must be discussed with local infection specialists and with the Imported Fever Service (IFS) (https://www.gov.uk/guidance/imported-fever-service-ifs) (24 hour telephone service: xx-xxxx-xxxx). The IFS can advise on whether laboratory testing is required. In the UK, the Rare and Imported Pathogens Laboratory (RIPL) (https://www.gov.uk/government/collections/rare-and-imported-pathogens-laboratory-ripl) at Porton Down is the designated diagnostic laboratory. The mainstay of NiV detection at RIPL is RT-PCR. Serology for Nipah antibodies is not available

Treatment

There is no proven, specific treatment for NiV infection, and there is currently no preventative vaccine. Several experimental therapies are in pre-clinical development or phase 1 clinical trials, including monoclonal antibodies, fusion inhibitors, and novel antivirals.

Clinical management of confirmed cases in England should be provided by specialist infectious diseases and critical care teams that are capable of safely managing patients with high consequence infectious diseases.

NiV is one of the pathogens in the World Health Organization’s (WHO) Research & Development Blueprint list of epidemic threats (https://www.who.int/teams/blueprint/nipah-henipaviruses#:~:text=Nipah%20virus%20is%20one%20of,human%20transmission%20have%20been%20documented.) requiring urgent research and development action, including animal and human vaccine development. Further information on experimental therapies and vaccine development is available from the WHO (https://www.who.int/publications/m/item/paramyxoviridae---landscape-of-vaccines-and-therapeutics-licensed-or-under-development-for-pathogens-being-considered-as-priority-pathogens).

Prevention and control

The risk of NiV infection can be reduced by avoiding exposure to pigs and bats in endemic areas and not drinking raw date palm sap. Studies have shown contamination of surfaces in hospitals during outbreaks, suggesting that there may be a risk of fomite-mediated transmission. Appropriate isolation is essential for suspected and confirmed cases. Strict contact, droplet and airborne infection prevention and control measures are required when caring for both suspected and confirmed patients.

Clinical laboratories should be informed in advance of samples submitted from suspected or confirmed NiV cases, so that they can perform local risk assessments, minimise risk to laboratory workers and, where appropriate, safely perform laboratory tests that are essential to clinical care. NiV is an ACDP/SAPO Hazard Group 4 pathogen (http://www.hse.gov.uk/pubns/misc208.pdf).

Cases in the UK

NiV does not occur in the UK, nor have any travel-associated cases been reported in the UK. The main risk activities for NiV infection are associated with local practices (for example, collection and consumption of raw or fermented date sap) that are generally not undertaken by tourists. The risk for other travellers such as those visiting friends and relatives or participating in local volunteer work may be higher dependent on activities undertaken.

Advice for travellers to endemic areas

Those travelling to endemic areas, particularly areas with active outbreaks, should avoid contact with bats and their environments, and sick animals. Consumption of raw or partially fermented date palm sap should be avoided. Wash fruit with clean water and avoid any fruit that has been partially eaten by animals or that may be contaminated (for example, windfall fruit).

For information about travel advice, see NaTHNaC (https://travelhealthpro.org.uk/).

Further information

See WHO Nipah virus collection (http://www.who.int/csr/disease/nipah/en/)