KOZHIKODE: Environmental changes, habitat disruption and increasing interaction between humans and wildlife could be contributing to the repeated emergence of Nipah in Kerala, according to a recent study that examined the ecological factors linked to recurring spillover events.
The study, ‘Two geographies, one virus: What recurrent Nipah spillover in India reveals’, published on May 13 by researchers Deepak Y Patil, Rima R Sahay, Sreelekshmy Mohandas and Pragya D Yadav, highlights how ecological conditions can influence the transmission of zoonotic diseases.
The researchers said deforestation, loss of natural habitats and increased human activity in biodiversity-rich regions may increase opportunities for viruses to cross from animals to humans.
Explaining the factors behind Nipah spillovers, Sreelekshmy said, “Kerala has reported Nipah outbreaks mainly between April and September, when the weather is hot and humid and seasonal fruits are widely available. During this period, bats often come closer to human settlements for feeding, increasing the possibility of contamination,” she said.
Sreelekshmy pointed out that fruit bats nesting near residential areas create opportunities for direct or indirect contact between bats, humans and domestic animals. However, Kerala’s strong disease surveillance mechanisms and rapid public health response have helped prevent larger outbreaks.
The study said Nipah virus (NiV), a highly infectious pathogen capable of causing severe illness in humans, is primarily maintained in Pteropus bats, commonly known as fruit bats. These are considered natural reservoirs of the virus and may carry it without showing severe symptoms.
The researchers noted that Kerala’s unique ecological landscape where forests, agricultural areas and densely populated settlements exist in close proximity creates conditions where human and wildlife interactions are frequent. Changes in land use, expansion of settlements and increasing pressure on natural habitats may force wildlife, including bats, to move closer to human environments in search of food and shelter, increasing the risk of pathogen transmission.
Tracking Nipah
2018: Kozhikode and Malappuram
23 confirmed cases, 17 deaths
First major Nipah outbreak in South India; significant transmission occurred, including within healthcare settings, but was contained through aggressive contact tracing and isolation measures
2019: Ernakulam
1 confirmed case, no deaths
Over 300 contacts monitored, preventing further spread
2021: Kozhikode
1 confirmed case, 1 death
12-year-old boy died, but strict quarantine measures prevented transmission
2023: Kozhikode
6 confirmed cases, 2 deaths
Authorities temporarily closed some institutions and strengthened prevention measures
2024: Malappuram
2 confirmed cases, 2 deaths
Both cases were isolated spillover events without reported secondary transmission
2025: Palakkad and Malappuram
4 confirmed cases, 2 deaths
Nipah detected in new areas, including Palakkad