What is the Nipah virus that is spreading fear across South Asia?

A recent cluster of Nipah virus cases in India’s West Bengal has triggered renewed concern across South and Southeast Asia. Authorities in Thailand, Malaysia and other neighbouring countries have ramped up airport screening as a precaution.

While the virus is rare, its high fatality rate and potential for human-to-human transmission make monitoring outbreaks a priority for health officials. Scientists are closely watching the situation, emphasising vigilance rather than panic.

But what is the Nipah virus, and how worried should people be?

What is the Nipah virus?

Nipah is a rare viral infection that spreads largely from infected animals, mainly fruit bats, to humans. It can be asymptomatic but it is often very dangerous, with a case fatality rate of 40 percent to 75 percent, depending on the local healthcare system's capacity for detection and management, the World Health Organisation says.

While the virus can also spread from person to person, it does not do this easily, and outbreaks are usually small and fairly contained, according to experts and the European Centre for Disease Prevention and Control. Candidate vaccines are under development, although none have been approved yet.

How common is it?

Nipah was first identified in Malaysia in 1999. Since then, there have been small outbreaks almost every year, mostly in Bangladesh. India also sees sporadic outbreaks. 

As of December, 750 cases had been recorded in total, and 415 of the patients died, according to the Coalition for Epidemic Preparedness Innovations, a group that tracks emerging disease threats and funds the development of medical tools to protect against them.

What are the symptoms?

The initial symptoms of Nipah such as fever, headaches and muscle pain are not specific and can be confused with other diseases. These can then be followed by neurological signs indicating acute encephalitis, or inflammation of the brain, and some people experience severe respiratory problems. 

Symptoms usually appear within a few days to two weeks after exposure, although longer incubation periods have been reported in some cases. Health officials say early detection is critical, as the disease can worsen rapidly once neurological symptoms develop.

Children and older adults, as well as people with underlying health conditions, are thought to be at higher risk of developing a severe form of the disease.

Seizures occur in severe cases, progressing to a coma in days. Most people who get better make a full recovery, but some experience long-term neurological problems.

How worried should we be?

While Nipah is a dangerous disease with a high fatality rate, it has not yet shown signs of becoming more transmissible among humans or spreading easily worldwide, scientists say.

Nearby Pakistan has already tightened surveillance and border screening as a precautionary response to the unfolding situation in India, despite having no confirmed Nipah cases to date.

Other countries across South and Southeast Asia have also strengthened health measures in response. Airports in Thailand, Malaysia, Singapore, Hong Kong, Indonesia and Vietnam have reinstated COVID‑style health screenings and temperature checks for passengers arriving from affected regions.

Similarly, Nepal has begun screening incoming travellers at Kathmandu and land border points with India as a precautionary step, even though no local cases have been confirmed.

However, it remains a significant public health concern, according to the WHO, particularly in countries where outbreaks are more common. It can also lead to the mass culling of farm animals such as pigs that are susceptible to the virus.

Scientists say, however, that it is unlikely to spread globally — and also point out that airport screening may be ineffective as the virus has a long incubation period.

What vaccines and treatments are available?

There are currently no approved vaccines or treatments for Nipah, although a number of candidates are undergoing testing, including one developed by the Oxford University scientists involved in developing one of the COVID-19 vaccines.

Their Nipah vaccine uses the same technology, and began phase II testing in Bangladesh in December in collaboration with the International Centre for Diarrhoeal Disease Research, Bangladesh, and with funding from CEPI.