There are currently no approved vaccines or treatments, although several candidates are being tested.
Two cases of the deadly Nipah virus in India have prompted authorities in Thailand and Malaysia to step up controls at airports to prevent the spread of the infection.
Later, Pakistan also ordered strict and enhanced health surveillance at all entry points following regional alerts.
But what is the Nipah virus and how worried should people be?
What is Nipah virus?
Nipah is a rare viral infection that spreads largely from infected animals, primarily fruit bats, to humans. It can be asymptomatic, but is often very dangerous, with a case fatality rate of 40% to 75%, depending on the detection and management capacity of the local health system, says the World Health Organization (WHO).
However, although it can also be transmitted from person to person, it does not do so easily and outbreaks are usually small and fairly contained, according to experts and the European Center for Disease Prevention and Control. Vaccine candidates are being developed, 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, mainly in Bangladesh. India also suffers from sporadic outbreaks.
According to the Coalition for Epidemic Preparedness Innovations (CEPI), a group that tracks emerging disease threats and funds the development of medical tools to protect against them, 750 total cases had been recorded as of December and 415 of the patients had died. Reuters tracked the spread of Nipah in a 2023 series, Bat ‌Lands.
Read more: Pakistan reinforces border surveillance due to Nipah virus
How is it spread?
When first identified in Malaysia, Nipah was largely spread through direct contact with sick pigs or contaminated tissues. Since then, it spreads most commonly by contact with what scientists say is its natural host: fruit bats. More specifically, consumption of fruits or fruit products, such as raw date palm juice, containing urine or saliva from infected fruit bats has been the most likely source of infection, the WHO says.
Human-to-human transmission has been found, mainly after close contact between a sick patient and his or her family or caregivers.
What are the symptoms?
The initial symptoms of Nipah, such as fever, headaches and muscle aches, are non-specific and can be confused with other illnesses. These may be followed by neurological signs indicating acute encephalitis or inflammation of the brain, and some people experience severe breathing problems.
Seizures occur in severe cases and progress to coma within days. Most people who improve 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 mortality rate, it has not yet shown signs of becoming more transmissible between humans or spreading easily around the world, scientists say. However, according to the WHO, it remains a major public health problem, especially in countries where outbreaks are most common.
It can also lead to mass culling of farm animals, such as pigs, which are susceptible to the virus. However, scientists say it is unlikely to spread globally and also point out that screening at airports may be ineffective as the virus has a long incubation period.
What vaccines or treatments are available?
There are currently no approved vaccines or treatments for Nipah, although several candidates are being tested, including one developed by Oxford University scientists involved in the development of one of the Covid-19 vaccines.
Its Nipah vaccine uses the same technology and began phase II trials in Bangladesh in December in collaboration with the Bangladesh International Center for Diarrheal Disease Research and with funding from CEPI.
