A 43-year-old man from Kerala’s Kozhikode district is critically ill on ventilator support with a suspected Nipah infection, again raising questions over how the deadly virus repeatedly spills over from bats to humans in the state.
Health officials have started contact tracing and containment measures without waiting for final laboratory confirmation from the National Institute of Virology in Pune. Five primary contacts have been identified and placed under observation, officials said.
For Kerala, the response has become familiar. Since its first Nipah outbreak in 2018, the state has built one of India’s strongest systems for detecting, isolating and containing the infection.
But the virus itself remains poorly understood in the Kerala context. Eight years after the first outbreak, scientists still do not know the precise route through which Nipah is passing from fruit bats to humans.
According to reports from Kozhikode, the patient had recently rented and cleaned a godown before developing fever. He later showed neurological symptoms suggestive of acute encephalitis.
As his condition worsened, he was moved between healthcare facilities before doctors suspected Nipah. Whether the godown had any link with fruit bat activity is still under investigation.
“There is no need for panic at this stage. The patient had recently rented a godown and cleaned it himself. We suspect he may have contracted the infection during that process,” Kerala Health Minister K Muraleedharan told reporters.
The minister said the patient initially developed a fever that subsided before returning more severely, eventually requiring intensive care. If confirmed, the case would mark another spillover event in a state that has seen repeated Nipah episodes since 2018.
Kerala recorded its first Nipah outbreak in Kozhikode and Malappuram districts in 2018, when 17 people died. The outbreak exposed risks in healthcare settings and reshaped the state’s approach to emerging infectious diseases.
A single spillover case was reported from Ernakulam in 2019. A 12-year-old boy died in Kozhikode in 2021. Kozhikode reported another cluster with limited human-to-human transmission in 2023. Last year, Malappuram emerged as the centre of multiple Nipah events.
One case involved a 42-year-old woman from Valanchery whose symptoms initially resembled dengue. When she failed to improve, doctors widened their investigations. Samples tested positive for Nipah at Kozhikode Medical College before confirmation from NIV Pune.
Authorities traced 112 contacts across several districts, with 54 categorised as high-risk. The response was swift, but the trigger remained unclear.
Research in vulnerable regions has consistently shown that Nipah virus detected in infected people and Pteropus medius fruit bats belongs to the same strain. Genome sequencing has repeatedly established the link between bats and human infections. But identifying the exact route of transmission has been far harder.
Dr T S Anish, nodal officer at the Kerala One Health Centre for Nipah Research and Resilience and professor of community medicine at Government Medical College, Kozhikode, has previously said index patients probably did not have direct contact with bats.
“It is improbable that any index cases had direct contact with the bats. However, they must have somehow come into contact with bat secretions,” he said during earlier investigations.
Researchers have examined several possibilities, including fruit contaminated with bat saliva or urine, and exposure to bat secretions in places where bats roost. But the evidence remains inconclusive.
Critical care specialist Dr Anoop Kumar AS, who has been involved in diagnosing and managing previous Nipah cases, has also highlighted the difficulty. Although fruit and environmental samples have been collected during outbreak investigations, the virus has not been isolated from these samples in Kerala. “All fruit samples have tested negative,” he has said.
Bangladesh, another Nipah hotspot, faced similar uncertainty before researchers identified contaminated date palm sap as an important transmission route. That finding helped shape targeted prevention measures.
Kerala has yet to identify an equivalent pathway.
The gap matters because, without knowing how spillovers occur, authorities are forced to respond after infections appear rather than prevent them.
Kerala’s approach increasingly follows One Health principles, which recognise the links between human, animal and environmental health.
During recent investigations in Malappuram, health officials conducted fever surveillance across thousands of households. The Health and Animal Husbandry departments jointly examined domestic animals for illness and collected samples where possible.
But officials say wildlife monitoring is difficult. “We are limited in including wild animals due to the difficulty of tracking and testing them. Therefore, our focus will be more on cats and dogs, which are more accessible and likely to have close contact with humans,” Malappuram District Surveillance Officer C Shubin said during earlier investigations.
Several affected areas lie close to forested landscapes bordering Wayanad. Outbreaks around Perambra, Kuttiyadi and the Janakikkad forests have drawn attention to changing interfaces between wildlife habitats, farms, settlements and workplaces.
NIV has detected Nipah virus circulation among fruit bats in Wayanad. The 14-year-old boy who died of Nipah in Malappuram in 2024 also came from an area close to the Wayanad landscape. Fruit bats play vital ecological roles in pollination and seed dispersal, and experts warn against demonising them.
The challenge is to understand whether habitat change, land-use shifts and changing human behaviour are creating new opportunities for viral transmission.
Kerala has designated Kozhikode, Malappuram, Kannur, Wayanad and Ernakulam as potential Nipah hotspots because of previous infections or evidence of viral circulation among bats.
Hospitals have strengthened infection-control protocols since 2018. Doctors now treat unexplained encephalitis with greater suspicion, and rapid isolation has become part of the state’s outbreak response.
These measures have helped prevent most spillover events from becoming large chains of transmission.
But that success also limits the time and number of cases available for detailed field investigations.
Scientists say rapid sharing of viral genome sequences is essential to understand whether Kerala’s Nipah strains are changing and how they relate to those seen in Bangladesh.
Nipah can cause severe encephalitis, respiratory illness and high mortality. It can also spread between humans in some circumstances.