Nipah

Nipah virus infection is a potentially deadly illness. It is transmitted to humans from animals through direct contact with them, their bodily fluids or tissues, or by consuming food contaminated by them.

It can also be transmitted from person to person, including to those caring for individuals with the infection, such as family members and health care workers.

Due to how easily the virus can spread, the World Health Organization lists Nipah virus as a ‘priority disease’ with the potential to cause serious epidemics or pandemics.

Nipah virus infection can range from no symptoms, to severe disease and even death. Because it can affect humans as well as other animals, outbreaks can have devastating effects on communities, both in terms of human health and economic losses for livestock farmers.

Outbreaks have been recorded across Asia. The first reported outbreak occurred in Malaysia and Singapore in 1999. More recent and recurrent outbreaks have been reported in India, with nearly annual outbreaks in Bangladesh. Evidence of the virus has been found in fruit bats and other bat species across multiple countries, including Cambodia, Ghana, Indonesia, Madagascar, the Philippines, and Thailand, suggesting that other regions could be at risk.

People usually start to feel unwell between 4 to 14 days after catching the virus (incubation period), but it can be as long as 45 days.

In humans who develop symptoms, Nipah virus infection usually starts with less specific symptoms such as fever, headaches, muscle aches, vomiting and sore throat, before potentially progressing to more severe disease.

It can be hard to recognise Nipah early on due to the initial symptoms being similar to other illnesses, but diagnosing it early and implementing timely infection control measures are important to prevent further transmission. 

The disease can progress to dizziness, drowsiness, altered consciousness and other signs that indicate that the brain is swollen due to the infection (encephalitis). In some cases, it can also affect the lungs, causing inflammation or infection that makes breathing difficult (pneumonia).  

Inflammation of the brain (encephalitis) and seizures occur in severe cases, progressing to coma within 24 to 48hrs. The fatality rate of Nipah varies by outbreak but is estimated to be 40-75%. Whilst many who survive make a full recovery, approximately 20% of survivors experience lasting neurological effects - including seizures or changes in personality.

A small number of those who recover may later become reinfected (relapse) or develop encephalitis at a later date.

Nipah virus can spread in various ways, including through direct contact with the tissue or bodily fluids of infected animals, infected humans, or food products that have been contaminated by the virus.

The initial outbreak in Malaysia and Singapore was related to infections in farmed pigs. It is thought that the pigs were initially infected by fruit bats, the natural animal reservoir for the virus, before the pigs then transmitted the virus to humans.

In Bangladesh and India, outbreaks appear more directly linked to fruit bats, with infections most commonly associated with eating fruit or fruit products, such as raw date palm juice, contaminated with the urine or saliva of infected bats.

Human-to-human transmission has also been documented in several outbreaks, with some close contacts and caregivers who were exposed to the bodily fluids of infected patients going on to develop the disease.

Prevention and Control Measures

Quarantining infected animals and restricting their movement, or safely culling them if required, may help to prevent the virus from spreading.

Minimising contact with infected pigs, and protecting pig feed and shelters from bats, are also important measures to reduce disease transmission.

Raising awareness of the risks associated with raw date palm juice and the benefits of boiling it before drinking is important. Fruits should also be carefully washed and peeled, and any fruits showing signs of bat bites should be discarded. Using protective coverings to prevent bats from accessing sap collection sites may also help reduce the risk of infection.

Natural Host

Whilst there is no apparent disease in fruit bats, they are believed to be the natural host for Nipah virus, and in particular fruit bats of the family Pteropodidae.

Diagnosis

The primary lab-based diagnostic tools used to confirm a Nipah virus infection are real time polymerase chain reaction (RT-PCR) tests – these are used to analyse bodily fluids and enzyme-linked immunosorbent assays (ELISA) which detects antibodies produced in response to Nipah virus infection.

The virus can also be confirmed by virus isolation by cell culture and polymerase chain reaction assays (PCR).

Vaccines in Development

Four vaccines for the prevention of Nipah virus disease have entered clinical trials. These include two viral vector vaccines (ChAdOx1 NipahB and rVSV-ΔG-EBOV-GP-NiVG), one protein-based recombinant subunit vaccine (HeV-sG-V), and one mRNA-based vaccine (mRNA-1215). To date, none of these candidates has received regulatory approval.