News of an outbreak of a deadly disease with “pandemic potential” will no doubt trigger flashbacks to the dark days of Covid when we were told to stay home and sing Happy Birthday twice while washing our hands. This time, it’s the bat-borne Nipah virus, a zoonotic infection with a death rate of between 40% and 75%, according to the UK Health Security Agency (UKHSA), that’s posing a problem.

The mention of a new outbreak of a potentially deadly disease brings back unsettling memories of the Covid-19 era, when we were advised to wash our hands while singing Happy Birthday twice. This time, the concern centers around the Nipah virus, a zoonotic infection that originates from bats and carries a fatality rate between 40% and 75%, as reported by the UK Health Security Agency (UKHSA).

In India, authorities are swiftly working to contain the virus after two healthcare workers in the eastern state of West Bengal became infected in late December. As of January 21, one patient remains on mechanical ventilation, while the other has shown improvements despite experiencing severe neurological symptoms. Approximately 200 individuals who came into contact with these workers have been identified and tested. Hospitals have heightened their infection control measures, and neighboring nations have tightened border security and initiated health screenings at key airports.

What is Nipah virus?

The World Health Organization has listed Nipah as one of its top ten priority diseases due to its potential to trigger an epidemic or pandemic. The UKHSA also identified it as a high-priority pathogen last March, highlighting the urgent need for the development of tests, treatments, and vaccines. To understand the implications of this virus, we consulted two experts in the fields of medicine and virology.

Nipah virus is a zoonotic illness that can jump from animals, such as bats and pigs, to humans. Fruit bats belonging to the Pteropodidae family are the primary carriers, spreading the virus through their saliva, urine, and feces without showing any symptoms themselves.

The pathogen was first identified in 1999 following a mysterious and deadly outbreak among pig farmers in Malaysia. Initially, health officials misdiagnosed the affected individuals with brain inflammation as having Japanese Encephalitis, a virus spread by mosquitoes. However, the persistence of fatalities led scientists to isolate and identify this new virus.

Transmission of Nipah can occur through direct contact with infected animals or their environments, contaminated food, or close interaction with an infected person. Consuming raw date palm syrup contaminated with the virus has also been identified as a potential transmission route.

Dr Efstathios Giotis, a lecturer in molecular virology at the University of Essex, said the current cases “seem to be contained”. “There is no evidence that there’s wider community spread and I haven’t read anything particularly worrying. There have been outbreaks of Nipah virus in the region in the past.”

What are the symptoms?

Dr Giotis described Nipah as a “serious disease”. “It can cause flu-like symptoms or it can invade the central nervous system and cause encephalitis, inflammation of the brain — that’s the most serious symptom,” the expert said. “That’s usually the main cause of death and it can cause long-term disability.”

Early symptoms typically include fever, headaches, muscle pain and vomiting, sometimes followed by dizziness and drowsiness. This can can progress to pneumonia and severe respiratory problems, seizures and coma.

Encephalitis occurs when the virus breaches the blood-brain barrier, leading to swelling and potentially causing lasting brain damage and neurological problems. This ability is what makes Nipah so lethal and why it is classified as a “neurotropic” virus, meaning one that targets the nervous system.

There are no specific treatments, so patients are given supportive care in hospital while their bodies fight the infection. People can also be infected without showing any symptoms, and the virus can sometimes reactivate months or even years after the initial infection.

Why is there no vaccine or treatment for Nipah?

The virus poses a challenge to researchers — it is very deadly, so treatments and vaccines are desperately needed. However, cases are relatively rare.

Prof Hunter explained: “The problem is that, because there are so few cases each year, proving a vaccine works in the real world takes a long time. I suspect that’s why [we don’t have a vaccine yet].

“With viral infections, sometimes antiviral drugs work, sometimes they don’t. Again, the problem is that, to know whether a treatment has benefit, you need to have enough cases.

“When you have a disease like Nipah virus, where outbreaks are generally small and in rural areas, the commercial pressure to develop something quickly isn’t as great. You might spend tens of millions bringing a drug to treatment, and then you can only use it three or four times a year in a low income country.”

Dr Giotis added: “Scientists are interested in it but because the outbreaks are rare and sporadic, that makes clinical trials a bit more difficult.”

How deadly is Nipah?

The death rate can vary between outbreaks, partly depending on local capabilities for identifying and containing cases. The UKHSA estimates that it falls between 40% and 75%, while Prof Hunter estimated that it ranges from 50% to 90%. “With a mortality rate like that, it is a substantially scary disease,” he added.

“You’ve probably got a 50% chance or more of dying, I think that’s pretty serious. It is a very nasty disease. Fortunately it’s not that infectious person-to-person at the moment.”

During the first outbreak among pig farmers, the virus appeared to only spread from animals to people. However, it was found to also spread from human to human during later outbreaks.

Could Nipah virus cause a pandemic?

Nipah inspired the 2011 Hollywood thriller, Contagion, which featured a virus called MEV-1 that triggers a global crisis. The fictional pathogen was transmitted from bats to pigs, and then to Gwyneth Paltrow via a handshake with a chef who did not wash his hands properly after handling raw meat.

There has never been a case of Nipah recorded in the UK and the potential for the current strain to cause a wider outbreak is considered low. But if it mutates to become more easily transmissible, it could quickly spread around the world.

Prof Hunter said: “Its pandemic potential is very low. It’s unlikely that it would cause more widespread outbreaks. Of course, viruses do have the potential to evolve, so I can’t guarantee that Nipah, at some point in the future, evolve to be more infectious.

“That hasn’t happened so far and, fingers crossed, it won’t in my lifetime. But we can’t just ignore it and say, ‘It’s not going to spread so we’ll just forget about it’.” This is why Nipah has been described by the World Health Organisation and UKHSA as a priority pathogen.

Dr Giotis said the virus does not spread as easily as other viruses such as flu, and doesn’t have the same ability to spread near-silently that made Covid so dangerous.

He added: “We need to see the genetic sequencing of this new strain, but so far we haven’t seen any evidence that the virus has changed in a way that makes it more transmissible or more lethal. The risk is quite low from what we’ve seen so far.”

Is it safe to go on holiday?

One of the major concerns around the India outbreak is that it coincides with a busy travel period, when people traverse Asia to celebrate the Lunar New Year.

Some airports in Thailand have started screening passengers arriving in Bangkok and Phuket from West Bengal, and the country’s parks and wildlife department has implemented stricter screenings at tourist attractions.

So what should you do if you have a holiday booked to an affected country? Prof Hunter said “most of the recent outbreaks have been in Bangladesh, West Bengal, Kerala”. He added: “There have been some elsewhere. The best advice is just be careful what you eat.

“There is a drink, palm tree sap, and sometimes it is fermented into an alcoholic beverage. That has been implicated several times so don’t drink juice that has not been pasteurised or heated, and make sure you peel fruit properly before you eat it — which is good advice for lots of things other than Nipah virus.

“Outbreaks occur most years but they generally are quite small. The risk is actually very low, particularly if you’re going to touristy areas.”

Dr Giotis similarly advised “some caution” but said the risk of infection for travellers is generally low. “Avoid contact with animals — bats, pigs — or sick individuals. Practice normal hygiene, hand washing, safe foods, avoid raw fruit juice. And of course seek medical care if you develop a fever after travelling.

“There’s no need to panic. Based on what we have heard so far, there’s no evidence of community spread so I don’t think travellers should panic. The whole situation seems to be low risk, just use common sense.”