PARIS: Named for the Malaysian village where it was first identified, the Nipah virus is an infectious disease transmitted primarily by bats.
Often fatal, its potential to spread has so far been considered limited by scientists.
Thailand, Malaysia and Singapore immediately strengthened their border controls.
While both outbreaks have occurred since early 2026 along the border between India and Bangladesh, the two recent clusters are not linked, World Health Organisation Director General Tedros Adhanom Ghebreyesus said on Wednesday.
No other cases have been identified after tracing more than 230 contacts.
At this stage, the WHO considers the risk of the virus spreading, both regionally and globally, to be “low”.
Fruit bats
The deadly Nipah virus was first identified in 1998 during an outbreak among pig farmers in Malaysia.
Generally transmitted to humans by an infected animal, usually fruit bats, but often also pigs or even horses, Nipah can also spread through contaminated food, or from person-to-person contact.
Currently, outbreaks of the Nipah virus are concentrated in South and Southeast Asia. An epidemic was reported in Singapore in 1999, when infected pigs were imported from Malaysia.
In 2001, India and Bangladesh also became the sites of outbreaks, with the former experiencing periodic outbreaks in the years since — most recently in early 2026.
The Philippines and Singapore have also recorded cases.
Respiratory and cerebral symptoms
While Nipah infection sometimes causes no symptoms, most infected individuals develop illness after an incubation period of three to 14 days — sometimes up to 45 days.
The initial symptoms — including fever, chills, sore throat, vomiting — are often nonspecific, but the condition can rapidly deteriorate and become serious.
Severe forms of the disease can cause serious neurological damage — including encephalitis, seizures, or even comas — or acute respiratory failure.
Its case fatality rate is estimated to be between 40 and 75%, depending on the individual case.
Survivors, for their part, generally recover completely. For about one in five, however, neurological after-effects persist, which can sometimes be debilitating.
Low transmissibility, high mortality
Unlike many respiratory viruses, such as Covid-19, the virus is not easily transmitted from one human to another.
It requires close and prolonged contact with respiratory secretions or bodily fluids from an infected person.
In India, recent cases have thus affected healthcare workers, and those who had been in contact with these patients were placed in quarantine.
Each infected person generally infects fewer than one other person, which limits the spread but does not prevent outbreaks.
But when this disease strikes, it is often fatal. And the WHO considers Nipah to be a high-risk pathogen.
No treatment, no vaccine
Currently, there is no specific antiviral treatment or vaccine for the Nipah virus. Doctors can only treat the symptoms.
Several vaccine candidates are currently being studied or are in development, most of them targeting proteins on the surface of the virus that are necessary for its entry into human cells and its spread throughout the body.
To reduce the risk of infection and transmission, prevention relies primarily on adapting behaviours: avoid consuming raw palm sap, wash and peel fruit, avoid fruit that has fallen to the ground or shows signs of bites, and limit contact with sick bats and animals.
Some countries also screen travellers arriving from affected areas.
Meanwhile, an Indian health worker who contracted the deadly Nipah virus in December has died, a senior health official from the eastern state of West Bengal said on Thursday.
The woman, a nurse, was one of two people in the state who were infected and was being treated at a local hospital, Reuters reported last month.
“The woman … who was critical, died due to cardiac arrest,” Health Secretary Narayan Swaroop Nigam told Reuters.
With additional input from Reuters