Is Your Region at Risk of a Nipah Outbreak?
A zoonotic Paramyxovirus, Nipah has caused terror among the inhabitants of south and south-east Asia. How did it suddenly emerge and how is it causing recurring epidemics? Many questions could be answered if we knew its spatiotemporal distribution and phylogeny. That’s exactly what a group of researchers from China and Australia tried to find out.
Ever since the first identification of the virus in 1998-99 up until 2021, 749 people from five countries (Bangladesh, India, Malaysia, Singapore and Philippines) and eight bat species across nine countries (including Thailand, Cambodia, Malaysia, Indonesia, Timor-Leste, Bangladesh and India) were documented as being infected with Nipah virus. Based on genomic studies, two clades were identified - the Bangladesh clade and the Malaysia clade and a common ancestor of these clades estimated to occur in 1863. The Nipah virus has been circulating for more than a hundred years among our midst! (Did we miss it while setting up the new world order?)
The Malaysia clade constituted strains from Malaysia, Thailand and Cambodia. The Bangladesh clade encompassed strains from Bangladesh, India and Thailand. In the era of artificial intelligence, is it any wonder that the evolutionary analysis and phylogeographic transmission routes could be analysed using softwares? The analysis showed that initially, the Malaysia clade spread from Malaysia to Bangladesh and then to Cambodia, whilst the Bangladesh clade first spread from Bangladesh to India and then to Thailand. (FYI: Thailand and Cambodia have not reported a human case of Nipah virus infection yet). The Bangladesh clade isolated from India formed two subclades - one from West Bengal and another from elsewhere in India. Wondering which one causes the nearly annual Nipah outbreaks in Kerala?
Based on 50 variables which were collected for this study that could potentially be associated with the occurrence of Nipah virus (31 environment-related, nine human activity-related and 10 animal-related), Bangladesh was found to have the largest predicted endemic area and largest at-risk population (106.7 million) for Nipah infection, followed by India (36.4 million), Thailand (16.5 million) and Malaysia (10.2 million). The case fatality rate (CFR) varies between the clades (adjusted CFR - 77% for Bangladesh clade and 37% for Malaysia clade). The CFR also varied between countries - 9% in Singapore and up to 78% in India.
Pteropus bats inhabit south Asia, south-east Asia as well as Australia, east Africa and islands within the Indian and Pacific oceans. Temperature related bioclimate variables significantly impacted the results of this study. These factors influence bat behaviour and migration and indirectly contribute to variations in Nipah virus transmission.
The authors recommend that zoonotic surveillance be strengthened in at-risk countries which haven’t reported human cases and that monitoring of potential modes of transmission be undertaken in India and Bangladesh.
Sun, Y.-Q. et al. (2024) ‘Mapping the distribution of Nipah virus infections: A geospatial modelling analysis’, The Lancet Planetary Health, 8(7). doi:10.1016/s2542-5196(24)00119-0.