Nipah virus infection - Bangladesh

Nipah virus is a zoonotic pathogen with a high death rate and no licensed vaccine or treatment, though early supportive treatment can save lives. Its reservoirs are fruit bats or flying foxes (bats of the Pteropus genus), which are distributed in the coastal regions and on several islands in the Indian ocean, India, south-east Asia and Oceania. The virus can be transmitted to humans from wild and domestic animals. Secondary human-to-human transmissions are also possible. Cases of Nipah virus infection were first reported in 1998 and since then have been reported in Bangladesh, India, Malaysia, Philippines and Singapore. The virus is present in Bangladesh, while NiV cases are reported throughout the year, outbreaks tend to occur between December and April corresponding with the harvesting and consumption of date palm sap. Clusters of cases are mainly reported in the country's central and northwest districts.

To date, since 2001 Bangladesh has documented 348 NiV disease cases, including 250 deaths, corresponding to an overall case fatality rate of 72%. Nearly half of these cases (n=162) were primary cases with a confirmed history of consuming raw date palm sap or tari (fermented date palm sap), while 29% resulted from direct person-to-person transmission. Most cases detected in Bangladesh were reported through December to April, suggesting a seasonal pattern. Based on the current available information, WHO assesses the overall public health risk posed by NiV at the national level to be low due to the following reasons:

The case fatality rate from NiV infection is high. There are currently no specific drugs or vaccines available for NiV infection, although WHO has identified Nipah as a priority disease for research under WHO Research and Development Blueprint. Intensive supportive care is recommended for the treatment of severe respiratory and neurologic complications. The initial signs and symptoms of NiV infection are non-specific, and the diagnosis is often not suspected at the time of presentation. This can delay timely diagnosis and create challenges in outbreak detection, effective and timely infection control measures, and outbreak response activities. Fruit bats (Pteropus spp.), as a natural reservoir of the Nipah virus, are present in Bangladesh and repeated spillover of the virus from its reservoir to the human population has been demonstrated. Despite ongoing efforts at risk communication and community engagement to address awareness, there is continued consumption of raw date palm sap by the community. However, the yearly number of NiV cases reported in Bangladesh remains under 10 since 2016, with exception in 2023 when 14 cases were reported. Although human-to-human transmission has been reported in previous outbreaks, it has been less frequent in recent years. In addition, strong public health measures are in place to detect and control outbreaks, including a hospital-based systematic human NiV infection surveillance system which has been established since 2006, the utilization of the National Rapid Response Team (NRRT) at the central level and the Rapid Response Team (RRT) at the district level and the capacity to rapidly test samples. Bangladesh borders India and Myanmar, and WHO assesses the risk at the regional level to be low. While there have not been any instances of cross-border transmission by humans previously, the risk remains, given shared ecological corridor for the virus's natural host Pteropus bats in Bangladesh and India. However, Bangladesh has strong capacities and experience of controlling previous NiV outbreaks.

WHO assesses the risk at the global level to be low, as there have been no previous confirmed cases outside Bangladesh, India, Malaysia, Philippines and Singapore.