Four unlinked Nipah deaths in Bangladesh, and one that broke the seasonal pattern

Between 1 January and 29 August 2025, Bangladesh notified WHO of four confirmed Nipah virus infections, all fatal, from four different districts across three separate divisions — Barisal, Dhaka and Rajshahi [s1]. All four were confirmed by RT-PCR and ELISA, and no epidemiological links were identified between them [s1].

Four deaths is a small number. What makes the report worth reading is the fourth case, which happened at the wrong time of year and through an unidentified route.

The three that fit the pattern

The first case was a young adult woman from Pabna district, Rajshahi division, with symptom onset on 25 January [s1]. She was admitted to a community hospital on 26 January, referred to another hospital the next day, and died on 28 January, with laboratory confirmation on 29 January [s1]. A total of 96 contacts were identified; all tested negative [s1].

The second was an adult man from Bhola district, Barisal division, who developed symptoms on 13 February, was admitted to hospital on 19 February, transferred the following day, and died on 22 February; infection was confirmed on 21 February [s1]. Seventy-one contacts were identified, all testing negative [s1].

The third was an adult man from Faridpur district, Dhaka division, with symptom onset on 17 February, admitted to hospital on 25 February and dead the same day, confirmed on 26 February [s1]. Sixty-six contacts were identified, all negative [s1].

All three had a history of consuming raw palm sap [s1]. This is the classic Bangladeshi exposure route: bats feed on sap collected overnight from date palms, and the sap is drunk fresh. It is also why Nipah in Bangladesh has a season — December to April [s1].

The fourth case did not fit

The fourth was a male child from Naogaon district, Rajshahi division, with symptom onset on 3 August [s1]. He was admitted to hospital on 8 August, moved to intensive care the next day, and died on 14 August [s1]. Samples collected on 10 August tested positive on 22 August, and an outbreak investigation team was deployed the same day [s1].

He had no history of consuming raw palm sap, and the likely source or sources of infection remain under investigation [s1]. WHO notes explicitly that this case was reported outside the typical season [s1].

Seventy-two contacts were identified; samples were collected from 11 symptomatic contacts, of which six tested negative, with the remaining results awaited at the time of the report [s1]. Fruit bats, the known reservoir, are present in the affected regions [s1].

An out-of-season case with no sap exposure is not evidence of a new transmission route on its own — a single case with an unidentified source is exactly the situation in which investigators most often end up finding a conventional exposure they initially missed. But it is the kind of signal that surveillance systems exist to flag, and it is why the deployment on the day of confirmation matters.

The context these four cases sit in

Bangladesh has documented 347 Nipah cases through its dedicated surveillance system since the first recognised outbreak in 2001, with a case fatality rate of 71.7% [s1]. Human infections have been detected almost every year since [s1]. Annual case fatality ratios have ranged from 25% in 2009 to 100% in 2024, when five laboratory-confirmed fatal cases were reported [s1].

Nipah is not confined to Bangladesh. Between 17 May and 12 July 2025, the Government of Kerala reported four confirmed cases including two deaths across two districts of the Indian state [s2]. Two were in Malappuram and two in Palakkad — the first confirmed cases in Palakkad district [s2]. Kerala has reported nine Nipah outbreaks since 2018, and India has seen infections repeatedly since 2001, including outbreaks in West Bengal in 2001 and 2007 [s2]. Since 1998, outbreaks have been reported in Bangladesh, India, Malaysia, the Philippines and Singapore [s2].

Why there is no treatment to discuss

There are currently no specific drugs or vaccines for Nipah virus infection [s1][s2]. Intensive supportive care is recommended to treat severe respiratory and neurologic complications [s1]. WHO's guidance for public health efforts is correspondingly narrow: raise awareness of risk factors, promote measures that reduce exposure, and detect cases early enough for supportive care to help [s1][s2].

Transmission is zoonotic — through infected animals such as bats or pigs, or food contaminated with their saliva, urine or excreta — and can also occur person to person through close contact [s1]. The incubation period ranges from 4 to 14 days, though an incubation period of up to 45 days has once been reported [s1].

The risk assessment

WHO assesses the overall public health risk from Nipah at the national and regional levels as moderate, with the risk of international spread considered low [s1]. In the Kerala event, WHO found no evidence of international human-to-human transmission and likewise assessed the risk of international spread as low [s2].

What to watch: whether the Naogaon investigation identifies a source, and whether the 2025–26 season beginning in December produces cases outside the palm sap route.

This article is informational and is not medical advice.

Sources

• [s1] World Health Organization, "Disease Outbreak News: Nipah virus infection – Bangladesh," 18 September 2025. https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON582
• [s2] World Health Organization, "Disease Outbreak News: Nipah virus infection – India," 6 August 2025. https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON577