Malaysia’s response to the first NiV outbreak in 1998 exemplified a holistic, multisectoral approach to outbreak containment and public health coordination. The outbreak resulted in 265 cases of acute encephalitis in humans, and 105 fatalities. It also had a considerable economic effect, as over a million pigs were culled to help to control the spread of the disease. Initially, the disease in pigs and farmers was thought to be African swine fever and Japanese encephalitis, respectively. The Malaysian government proactively implemented measures, such as vector control and vaccination, to combat Japanese encephalitis. However, these efforts were unsuccessful, as case numbers continued to rise and the outbreak spread to Singapore in March 1999. Many healthcare workers suspected that this could have been a novel virus, as the symptoms were not typical of Japanese encephalitis. In addition, many of the patients who reported cases had been vaccinated against Japanese encephalitis. The isolation of the aetiological agent NiV from the cerebrospinal fluid of some patients was the turning point that led to successful outbreak containment.
The first known NiV outbreak in Bangladesh occurred in 2001 in the Meherpur district, located in the western part of the country. NiV outbreaks in the country are typically linked to the consumption of raw date palm sap contaminated with NiV. The largest outbreak recorded to date was in 2004, which had 67 confirmed cases2. Since then, Bangladesh reports cases nearly every year. In 2006, the government established an active NiV surveillance system as a control measure, through the Institute of Epidemiology, Disease Control and Research in collaboration with the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR, B) and technical support from the US Centers for Disease Control and Prevention. The NiV outbreak that occurred in 2023 recorded 14 cases. From 2001 to 2024, a total of 343 NiV cases were reported (Fig. 1), which resulted in 245 deaths.
The map presents an epidemiological analysis to support public health planning by visualizing the spatial distribution of reported cases. Colour-coded districts highlight high-risk areas. Data are from 2001 to 2025. Credit: Map preparation: Dr. Maruf Ahmed Bhuiyan, Lab research Officer, Characterizing the Epidemiological Diversity of Nipah Strains from Bangladesh, IEDCR and Dr Mintu Chowdhury Project Coordinator, Characterizing the Epidemiological Diversity of Nipah Strains from Bangladesh, IEDCR.
India reported its first NiV outbreak in 2001 in Siliguri, West Bengal3. Initially, the outbreak was believed to be caused by the measles virus. Nearly five years later, the samples collected were retrospectively tested, and NiV infection was confirmed. Since then, 4 confirmed NiV outbreaks have occurred, which have resulted in a total of 90 recorded cases between 2007 and 2021. The 2007 NiV outbreak took place in West Bengal state, near the Bangladesh border. Bat surveys in West Bengal and nearby Assam state revealed the presence of NiV antigens and antibodies in bats of Pteropus sp. Drawing from the Malaysia experience, 1,113 pigs were screened for NiV antibodies, but all were found to be negative.
The subsequent outbreaks (2018, 2019 and 2021) occurred in a geographically distant location in the southernmost state of the country, Kerala. The outbreaks in India have been linked to infected bats in endemic areas. In response to the repeated outbreaks, the Indian Council of Medical Research initiated a nationwide bat survey to better understand the distribution of NiV across the country. Although the survey is still ongoing, it has already detected the presence of antibodies in populations from multiple states.
