An outbreak of the deadly Nipah virus in India’s West Bengal state has raised concerns in parts of Asia, prompting increased screening at some airports.

Thailand has started screening passengers at three airports serving flights from West Bengal. Nepal has also started screening arrivals at Kathmandu airport and other land border points with India.

In West Bengal, two healthcare workers have reportedly been infected since December. About 196 people who came into contact with them were traced and tested negative for the virus, India’s Ministry of Health said.

Viruses can be transmitted from animals to humans. Because there is no vaccine or treatment, the mortality rate is high, ranging from 40% to 75%.

What is Nipah virus and what are its symptoms?

Nipah virus can be transmitted to humans from animals such as pigs and flying foxes. It can also be transmitted from person to person through contaminated food.

The World Health Organization has listed Nipah virus among its top 10 priority diseases, along with pathogens such as Covid-19 and Zika, due to its potential to cause epidemics.

The incubation period is 4 to 14 days.

When infected with a virus, you may experience a variety of symptoms or no symptoms at all.

Early symptoms include fever, headache, muscle pain, vomiting, and sore throat. Some people may later experience drowsiness, altered consciousness, or pneumonia.

Encephalitis is a sometimes fatal condition that causes inflammation of the brain and can occur in severe cases.

To date, no vaccine or drug has been approved to treat this disease.

Where has it occurred in the past?

The first recognized Nipah outbreak occurred among pig farmers in Malaysia in 1998, and has since spread to neighboring Singapore. The virus is named after the village where it was first discovered.

More than 100 people have died and 1 million pigs have been culled to contain the virus. It also caused huge economic losses to farmers and people involved in the livestock trade.

Bangladesh has borne the brunt in recent years, with more than 100 people killed in Nipah since 2001.

The virus has also been detected in India. Outbreaks were reported in West Bengal in 2001 and 2007.

Recently, the southern state of Kerala has become a Nipah hotspot. In 2018, 19 cases were reported, of which 17 were fatal. And in 2023, two of the six confirmed cases later died.

What is happening now?

India’s Ministry of Health said that after a case was confirmed in West Bengal state, contacts of the infected person were “identified, traced, monitored and tested” and were found to be asymptomatic.

“The situation is being continuously monitored and all necessary public health measures are in place,” the ministry said.

No cases have yet been reported outside India, but several countries have stepped up precautions.

Thailand on Sunday began screening passengers at three international airports in Bangkok and Phuket, which serve flights from West Bengal. Passengers on these flights are required to declare their health status.

The Parks and Wildlife Department also carries out rigorous inspections of natural tourist attractions.

July Wongswasdi, a spokesperson for the Ministry of Disease Control, told the BBC that Thai authorities were “quite confident” in guarding against the outbreak in Thailand.

Nepal has also started testing people arriving through Kathmandu airport and other land border points with India.

Meanwhile, Taiwanese health authorities are proposing to register Nipah virus as a “Class 5 disease.” Under the island system, diseases classified as Category 5 are emerging or rare infectious diseases that pose a significant public health risk and require immediate reporting and special control measures.

Correction: An earlier version of this story said at least five people had been infected in West Bengal, but India’s Ministry of Health later issued a statement saying there had been only two confirmed cases in the state since December.