Health authorities in India and across parts of Asia are on high alert following the confirmation of two cases of the deadly Nipah virus in the Indian state of West Bengal.

The cases, both healthcare workers at the Narayana Multispeciality Hospital in Barasat, 16 miles from Kolkata, have prompted nationwide surveillance measures and heightened screening at airports and border crossings in neighbouring countries.

The patients, both nurses, developed high fevers and respiratory distress between December 31 and January 2, and were admitted to intensive care on January 4. One remains in a coma, according to media reports.

Investigations suggest the virus was contracted while treating a patient with severe respiratory symptoms, who later died before testing could be carried out. Authorities are treating this individual as the suspected index case.

So far, 196 people who came into contact with the nurses have been traced and tested, with 20 high-risk contacts quarantined. All have tested negative and remain asymptomatic.

“We will test them again before their 21-day quarantine ends,” said Narayan Swaroop Nigam, Principal Secretary of West Bengal’s Health and Family Welfare Department.

There is no approved vaccine or treatment which can spread from animals such as bats and pigs to humans, as well as person-to-person through contaminated food, saliva, or respiratory droplets.

The virus has a high fatality rate – from 40% to 75% – while symptoms include fever, headache, vomiting, respiratory distress, and, in severe cases, encephalitis.

In a countrywide alert, India’s Ministry of Health urged states to strengthen detection and preventive measures.

In Tamil Nadu, hospitals have been instructed to monitor all cases of Acute Encephalitis Syndrome (AES), which can signal undiagnosed Nipah infections, particularly in patients with travel or contact links to West Bengal.

Kerala health officials noted that last year, more than 100 AES cases were reported, many of which could have been undiagnosed Nipah infections.

Neighbouring countries are also taking precautionary measures. Thailand has begun screening passengers arriving from West Bengal at three airports, while Nepal has implemented screening at Kathmandu airport and other land border points with India.

“The World Health Organisation lists Nipah as one of its top ten priority diseases because of its epidemic potential,” said experts.

The incubation period ranges from four to 14 days, and symptoms may sometimes appear mild or even absent, making early detection difficult.

Authorities are expanding testing criteria and laboratory protocols to capture possible cases of Nipah and other emerging infections presenting with AES-like syndromes.

“When cases are not recognised early, healthcare workers are placed at the highest risk of exposure to this often fatal virus,” said a senior health official involved in West Bengal’s surveillance efforts.