What makes Kerala susceptible to Nipah virus outbreak?

Why Nipah virus outbreaks are occurring only in Kerala
PREMIUM
With fruit bats positive for Nipah virus antibodies seen in other States, it is likely that Nipah virus infection and deaths may be going undetected in other States while they get picked up in Kerala, especially in Kozhikode district
Health workers wait to admit patients at a Nipah isolation ward at the Medical College, in Kozhikode on Friday. | Photo Credit: PTI

Since May 2018 when Kerala reported the first Nipah outbreak in Kozhikode district, there have been three more outbreaks of Nipah virus including the latest one in late-August 2023. For reasons still not known, three of the four Nipah outbreaks in Kerala in 2018, 2021 and 2023 have been in Kozhikode district; the 2019 outbreak was in Ernakulam district.

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Even five years after the first outbreak in Kerala, and four outbreaks in all, it is still unclear why three of the four outbreaks have been in Kozhikode district in Kerala. Fruit bats that can cause Nipah virus outbreaks in humans are not restricted to Kozhikode district.

As per a 2021 study, Nipah virus was found to be in circulation in fruit bats (Pteropus species) in “many districts” in Kerala. An ongoing nationwide survey in 14 States by NIV Pune has found Nipah virus antibodies in fruit bats (Pteropus medius) in nine States, including Kerala, and the Union Territory of Pondicherry.

While date palm sap was linked to Nipah virus outbreaks in Bangladesh, and pigs acting as intermediate hosts were responsible for Nipah outbreaks in Malaysia, the route of virus transmission from bats to humans has not been clearly established in Kerala.
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