The story so far

Kerala’s first encounter with Nipah virus (NiV) was in 2018, which identified 23 cases (including 18 lab-confirmed ones). The case fatality rate was 91% and there were two survivors. Since then, Kerala has recorded numerous spillovers of NiV.

In 2019, a lone case was identified in Ernakulam and the 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 single cases each 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 reported that none of these cases appeared to be linked to each other, suggesting independent spillover events from the natural reservoir.

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

Why is Nipah recurring in Kerala?

Research has consistently identified the Indian flying fox bat (Pteropus medius) or the fruit bat as the natural reservoir of Nipah virus in Kerala. Serological studies and viral detection in bats have shown that the virus is circulating in bat colonies in the State, particularly in northern districts.

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

The Pteropus species are found across the State and very near human settlements. A mapping study of bat-roosting sites by Kerala Forest Research Institute’s Department of Wildlife Biology had found that almost all of the roosts were near human habitats, increasing the risk of zoonotic exposure.

The recurrent NiV spillovers in Kerala with fair regularity suggest that the virus has established itself in the environment. The peak Nipah virus spillover risk in the State is from April to September, when the abundance of seasonal fruit-laden trees, increased bat foraging activity, bat breeding season and viral shedding dynamics coincide, increasing the risk of human exposure. This pattern has not changed in Kerala since the very first outbreak.

Because of the perennial natural virus reservoir in the State, it might not be possible to prevent recurrent NiV spillover events in Kerala.

What makes Kerala particularly vulnerable to zoonotic diseases?

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

The Western Ghats, which stretches along the State’s eastern flank, is one of the world’s richest biodiversity spots and the tropical rainforest climate sustains several hundred species of birds, reptiles and mammals. But only about 160,000 sq km of this rich biosphere is formally protected. The high population density in Kerala and the increased presence of human settlements, plantations, and agricultural lands immediately adjacent to and along the forest fringes increases the opportunities for human-wildlife interactions and facilitates exposure to novel pathogens.

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

Nipah is just one among Kerala’s broader zoonotic risk profile, which includes other pathogenic diseases like Kyasanur Forest Disease (KFD), leptospirosis, scrub typhus, Japanese encephalitis, West Nile fever, rabies and avian influenza.

The World Health Organisation (WHO) has warned Kerala to be on the vigil about some high threat 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 recurrent threat of zoonotic events like Nipah?

Nipah has been classified by the WHO as a priority pathogen because of its lethality, unpredictability and its alarming potential to cause widespread outbreaks or even the next pandemic. The recurrent spillover incidents in Kerala has primed the health system about the importance of sharp and coordinated disease surveillance, rapid pathogen identification and containment efforts to ensure that human-to-human transmissions do not occur, resulting in a wide outbreak.

The 2018 brush with Nipah took the health system by surprise. Of the 23 cases identified in the outbreak, only the index case had contracted the infection in the community. All the remaining cases were due to nosocomial transmission in three different hospitals.

Kerala used the 2018 experience as an opportunity to develop a clinical algorithm for all emerging viral infections at tertiary care levels, strengthen diagnostic and research capacities and augment standard infection control practices in hospitals. Clinicians in the State have become adept at maintaining a high index of suspicion when they encounter unusual cases of acute encephalitis syndrome and to watch for clustering of cases.

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

In all its Nipah outbreaks, the health system’s public health response has demonstrated that it can rapidly identify the index case and swiftly contain the event. After the initial event, human-to-human transmission has occurred only once in 2023.

What future strategies should Kerala adopt?

The recurrence of Nipah in Kerala and the State’s swift public health response every time has been a demonstration of the resilience of the State’s health system. With the State harbouring a natural reservoir of NiV and a perennial risk of virus spillovers, the Health department’s focus has been on creating community awareness about the situation so that the bat-human interface is reduced.

As part of its ‘One Health’ strategies, it has developed a massive community-based surveillance network supported by over 2.5 lakh trained volunteers at the grassroots, who track and report unusual disease trends, including unusual animal or bird deaths, to enable early detection of zoonotic outbreaks such as Nipah and Mpox.

In 2023, the State set up the One Health Centre for Nipah Research and Resilience at Kozhikode, which has been focusing on building community awareness, resilience and capacity to minimise spillover events and to mount a swift response to any such events. It has documented every single outbreak in Kerala and prioritised Nipah research for the future, focusing on disease epidemiology, sero surveillance studies and host factors research.

The State government, along with NIV, is also involved in a project to develop indigenous monoclonal antibodies against Nipah, specific to the Bangladesh strain of NiV circulating in Kerala.