Zoonotic potential of Kerala in the backdrop of Nipah

The story so far

Kerala’s first encounter with Nipah virus (NiV) was in 2018 when 23 cases (including 18 laboratory confirmed) were identified. Case fatality was 91% and two survived. Since then, Kerala has seen numerous NiV spillovers.

In 2019, a single case was identified in Ernakulam and that person survived the infection. In 2021, a 12-year-old boy was detected with the infection in Malappuram. In 2023, Nipah resulted in a cluster of six cases in Kozhikode. In 2024, two individual cases were reported from separate spillover events from Malappuram in July and September of that year. In 2025, four cases of Nipah were reported from two districts, Malappuram and Palakkad, and epidemiological investigations indicated that none of the cases appeared to be related, suggesting independent spillover from a natural reservoir.

NiV has now resurfaced in Kozhikode and a 43-year-old man who tested positive for the virus is fighting for his life at Kozhikode Medical College.

Why is Nipah recurring in Kerala?

Research has consistently identified the Indian flying bat (Pteropus medius) or bat as the natural reservoir of Nipah virus in Kerala. Serological studies and virus detection in bats have shown that the virus is circulating in bat colonies in the state, especially in the northern regions.

In the 2018 outbreak in Kerala, about 25% of bat samples were found to be positive for Nipah virus RNA, and in subsequent events, bat samples also revealed the presence of NiV.

Pteropus species are found throughout the state and very close to human settlements. A mapping study of bat roost sites by the Wildlife Biology Department of the Kerala Forest Research Institute found that almost all roost sites were located near human habitations, increasing the risk of exposure to zoonotic disease.

The recurrent shedding of NiV in Kerala with fair regularity suggests that the virus has become established in the environment. The highest risk of Nipah virus spillover in the state is from April to September, when the abundance of seasonal fruit trees, increased foraging activity of bats, the breeding season of bats and the dynamics of virus spread coincide, increasing the risk of human exposure. This pattern has not changed in Kerala since the first outbreak.

Due to the persistent natural reservoir of the virus in the state, it may not be possible to prevent recurrent NiV spillover events in Kerala.

Why is Kerala particularly prone to zoonotic diseases?

It is the convergence of ecological, demographic, climatic factors and increased human-wildlife interface that makes Kerala a special laboratory for zoonotic diseases.

The Western Ghats, which run along the eastern flank of the state, are one of the richest places in the world for biodiversity, and the tropical rainforest climate supports several hundred species of birds, reptiles and mammals. But only about 160,000 km2 of this rich biosphere is formally protected. Kerala’s high population density and the increased presence of human settlements, plantations and agricultural land immediately adjacent to and along forest edges increase opportunities for human-wildlife interactions and facilitate exposure to new pathogens.

Scientific literature links emerging zoonoses to deforestation, habitat fragmentation, urbanization and agricultural intensification. When wildlife habitats are disturbed, animals are forced into closer contact with human settlements and cultivated food sources. Scientists also warn that climate-related ecological disruptions could be a significant contributor to the future risk of Nipah spillover.

Nipah is only one of Kerala’s wider zoonotic risk profile, which includes other pathogenic diseases such as Kyasanur Forest Disease (KFD), leptospirosis, typhoid, Japanese encephalitis, West Nile, rabies and bird flu.

The World Health Organization (WHO) has warned Kerala to be on the lookout for some highly hazardous pathogens (HTPs) – Nipah, Avian Influenza (H5N1) and KFD – which have a high mortality profile and high transmissibility with pandemic potential.

How is Kerala responding to the recurring threat of zoonotic events like Nipah?

Nipah has been classified as a priority pathogen by the WHO due to its lethality, unpredictability and its alarming potential to cause large-scale outbreaks or even another pandemic. Recurring spillover cases in Kerala have alerted the health system to the importance of sharp and coordinated disease surveillance, rapid identification of pathogens, and containment efforts to ensure that human-to-human transmission does not occur, resulting in a large-scale epidemic.

The brush with Nipah 2018 caught the health system by surprise. Of the 23 cases detected in the outbreak, only the index case was infected in the community. All remaining cases were due to nosocomial transmission in three different hospitals.

Kerala used the experience of 2018 as an opportunity to develop a clinical algorithm for all emerging viral infections at the tertiary care level, strengthen diagnostic and research capacity, and expand standard hospital infection control practices. Clinicians in the state have become adept at maintaining a high index of suspicion when encountering unusual cases of acute encephalitis syndrome and watching for clusters of cases.

The state now has a strict system for monitoring all cases of acute encephalitis of unknown etiology, screening for severe respiratory infections, as well as timely laboratory confirmation and detection of pathogens through expanded VRDL (Virus Research and Diagnostic Laboratory) networks and intensive health emergency management measures.

The public health response of the health system in all Nipah virus outbreaks has proven to be able to quickly identify the index case and quickly stop the event. After the initial event, there was only one human-to-human transmission in 2023.

What future strategies should Kerala adopt?

The repeated occurrence of Nipah in Kerala and the prompt response of the state’s public health each time was a demonstration of the resilience of the state’s health system. Since the state is a natural reservoir of NiV and a constant risk of spreading the virus, the health department has focused on creating community awareness of the situation to reduce the bat-human interface.

As part of its “One Health” strategies, it has developed a massive community-based surveillance network supported by more than 2,500 locally trained volunteers who monitor and report unusual disease trends, including unusual animal or bird deaths, to enable early detection of outbreaks of zoonotic diseases such as Nipah and Mpox.

In 2023, the state established the One Health Center for Nipah Research and Resilience in Kozhikode, which focuses on building community awareness, resilience and capacity to minimize spillovers and respond quickly to any such events. He documented every single outbreak in Kerala and prioritized Nipah research for the future, focusing on epidemiology of the disease, serosurveillance studies and research on host factors.

The state government along with NIV is also involved in a project to develop original anti-Nipah monoclonal antibodies specific for the Bangladeshi strain of NiV circulating in Kerala.

Published – 13 Jun 2026 16:57 IST