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The source of the Nipah infection in West Bengal remains unconfirmed, with two possible routes under investigation
Officials are examining exposure to bat-contaminated date palm sap near the Bangladesh border and contact with a patient treated by the nurses
No additional cases have been detected so far
The source of the Nipah virus infection detected in West Bengal — the first such cases in the state in 19 years — remains unclear, with investigators examining two possible routes of transmission.
So far, two nurses have tested positive for the virus. Both are hospitalised and, according to state health department sources, are showing marginal improvement, though they remain at risk.
Initial investigations suggested that the infection may have originated in a village in Nadia district, close to the Bangladesh border. However, officials are also examining whether the nurses may have contracted the virus while treating a patient who later died with severe respiratory symptoms.
According to preliminary findings, one of the affected nurses had travelled to a village in Krishnaganj block of Nadia district, less than three kilometres from the India-Bangladesh border, to attend a social function, on December 15.
The area lies close to parts of Bangladesh where low to moderate levels of Nipah infection have been reported regularly over the past two decades. Investigators believe the nurse may have been exposed to the virus by consuming raw date palm sap or other contaminated food during her visit, a known risk factor for Nipah transmission.
However, a second possible route emerged on January 15. Health officials confirmed that both nurses had attended to an elderly woman in Barasat, on the northern outskirts of Kolkata, who was admitted with acute respiratory distress and an undiagnosed fever. The patient was treated on December 20 and 21 and died on December 22. No Nipah test was conducted before her death, making it difficult to confirm whether she was infected. Subsequent enquiries at her home indicated that she had symptoms similar to those associated with Nipah virus infection.
According to state health department officials, the infection has so far been limited to the two nurses. Around 150 contacts have been traced, placed under home quarantine and tested. 40 samples have been sent so far and have returned negative results, including those of 13 people believed to have had close contact with the nurses.
Samples from a nurse and a hospital staff member at Burdwan Medical College, admitted on January 14 with Nipah-like symptoms, also tested negative.
The initial positive results were identified at All India Institute Of Medical Sciences (AIIMS), Kalyani and later confirmed by the National Institute of Virology, Pune.
State health secretary NS Nigam on January 15 told this reporter that West Bengal was “fully prepared” to deal with the situation. In a rare show of coordination in the poll-bound state, Union Health Minister J P Nadda and West Bengal Chief Minister Mamata Banerjee discussed the developments and agreed on joint action.
While no public advisory has yet been issued for the general administration, the state health department has circulated detailed guidelines to both government and private hospitals on handling suspected Nipah cases.
An expert medical team has also arrived from Delhi to support the state’s response. In a video statement, Mr Nadda said the central government firmly stood with the state government and the Centre was providing “comprehensive technical, logistical and operational support” to contain the outbreak. The secretary for health and family welfare had held a discussion with the chief secretary and health secretary of the state to review the situation upon receiving the information about the case, he added.
Nipah virus is considered highly dangerous due to its high fatality rate, estimated to range between 40 per cent and 75 per cent. The virus can cause severe illness, including encephalitis, or inflammation of the brain.
It is transmitted from animals — particularly fruit bats — to humans, often through contaminated food such as raw date palm sap, or through direct contact with infected individuals.
In both West Bengal and Bangladesh, outbreaks have frequently been linked to bat-contaminated date palm juice, which is widely consumed during the winter months.
Health officials say Ghoghragachi village in Krishnaganj block, Nadia district, which is about 85 kilometres north-east of Kolkata, is among the locations being closely examined. A report by AIIMS Kalyani highlighted the village’s proximity to Bangladesh districts such as Chuadanga, Kushtia and Rajshahi, where Nipah cases have been recorded repeatedly since 2001.
According to a Bangladesh report accessed by this correspondent, more than 30 Nipah cases have been reported in Rajshahi, and between 11 and 20 cases each in Meherpur and Kushtia over the past two decades. The village in Krishnaganj block is 55 km from Meherpur, 81 km from Kustia and 120 km from Rajshahi.
A World Health Organization report noted that between January 1 and August 29, 2025, Bangladesh notified the WHO of four confirmed fatal Nipah cases across districts in Barisal, Dhaka and Rajshahi divisions.
Officials at AIIMS Kalyani said infrared surveillance in border regions has recorded fruit bats feeding on raw date palm sap — a known transmission pathway. “It is suspected she consumed raw date palm sap during the visit,” said a researcher associated with the investigation. “Fruit bats are attracted to the sap during this season and can contaminate it with saliva, urine or faeces, which can transmit the virus to humans.”
West Bengal chief secretary Nandini Chakraborty said on January 12 that the situation was being closely monitored.
“This virus comes from bats. People must be careful about what bats eat and what humans consume,” she said, adding that both nurses had also travelled to East Bardhaman, expanding the scope of contact tracing.
Officials expressed cautious relief on January 15 as no new cases had emerged since January 12.
Experts have urged the public to remain alert but calm.
“Nipah has a high fatality rate, but it rarely spreads from human to human and usually remains localised,” said Tapan Mukherjee, an adviser to the Kolkata Municipal Corporation’s health department. Subhrajyoti Bhowmick, a clinical pharmacologist at a private hospital in Kolkata, said avoiding bat-contaminated food, especially raw date palm sap, was crucial.
“Routine surveillance of human samples and bat populations was essential to prevent further spread,” Saumitra Das, professor at the Department of Microbiology and Cell Biology of Indian Institute of Science and former director of the National Institute of Biomedical Genomics.