They suggest that the boy may have eaten a wild hog plum (Ambazhanga in Malayalam) from a local area that could be a foraging site for Pteropus medius, also known as the fruit bat. The assumption is that the hog plum, infested with the virus due to contact with bats, could be the source of the infection. This chain of events, however, is yet to be scientifically validated.

Despite the mass destruction of bat colonies across the state and the continuous study of samples at the National Virology Institute in Pune and other leading research centres, the bat connection to the spread of the zoonotic disease remains unconfirmed.

Kerala has reported Nipah virus infections almost every year since 2018. As a result, local communities have targeted bats, regardless of their species. However, scientists have pointed out that only the large fruit bats of the Pteropus genus are the natural reservoir of the virus.

Health Minister Veena George told Hindustan Times that the areas the boy and his friends frequented will be monitored to confirm the presence of bats and establish the source of infection. She said the inability to identify the routes by which the virus infects patients continues to pose a challenge to the state's healthcare system.

The Central and State Animal Welfare Boards had caught bats from the affected areas, including the home of Maruthonkara Mohammed Ali, considered the index case in September last year. However, all samples were negative.

N M Arun, a Palakkad-based public health activist, said: "Only when clarity is reached regarding the transmission route will preventive measures become foolproof."

In Kerala, northern Kozhikode reported Nipah outbreaks in 2018, 2021, and 2023, triggering nationwide concerns. Adjacent Malappuram reported cases in 2018 and 2024. Ernakulam, a little further away, recorded a single case in 2019.

Some local doctors cite a study by the Indian Council of Medical Research (ICMR), which found Nipah virus antibodies in bats from Kozhikode and Wayanad, which have not yet reported Nipah outbreaks. The study also notes that the reasons behind the virus' localised impact and its transmission in humans remain unclear.

Though the Kozhikode-Malappuram region is home to a large population of fruit bats, experts believe various factors contribute to outbreaks in this area, including climate change, environmental degradation, and the characteristics of initial cases (the first people to contract the virus from animals).

"When Nipah was first reported in Malaysia in 1998, it was observed that bats affected by El Niño came closer to urban areas in large numbers. In Bangladesh and Bengal, the outbreak was linked to bat excreta. A clear connection is yet to be established in the case of Kerala outbreaks, but a common factor exists among the victims (index cases). They are all males, aged 12 to 25, who are active and adventurous," explained A. Althaf, a public health expert and professor at Government Medical College Hospital in Thiruvananthapuram.

An animal pathologist who conducted extensive research on bats in Kozhikode in 2018 said, on the condition of anonymity, that virus-carrying bats may not be limited to the Kozhikode and Malappuram regions alone.

"There are bats everywhere. Many places in Kerala have conditions similar to those in Kozhikode, including mangroves and urban forests. We need to determine if certain bat colonies harbour more viruses and the factors behind them. It is proven that bats release more viruses when stressed during birthing, food scarcity, overcrowding, and inclement weather," he said, adding more studies are required to establish bats' role in spreading the disease in the state.

Malaria, amoebic meningoencephalitis, and now Nipah — Kerala has of late been witnessing outbreaks of several zoonotic diseases despite its long legacy of maintaining a quality public health system.

According to experts, dense forest cover, extreme climate changes, and a large migrant population make the state prone to such infections.

Dipu T S, associate professor of infectious diseases in the Department of Internal Medicine at Amrita School of Medicine, warned that the risk of zoonotic diseases increases with greater human-animal interaction.

As human-animal interaction grows, so does the likelihood of these viruses spreading from animals or birds to humans. Humans may lack the natural immunity to viruses circulating among animals and birds.

Dipu emphasised that diseases spread when boundaries between species are breached. He noted that, as an ecosystem, it's not possible to eliminate these viruses and bacteria. However, he stressed the importance of caution to prevent the spread of these diseases.

Rajeev Jayadevan, chairman of the state IMA research cell, mentioned that the Nipah virus is known to circulate naturally in fruit bats. However, he said the exact transmission process to humans is still unknown.

Dipu added that climate change can contribute to the spread of certain viruses.

"Diseases like leptospirosis and dengue are often seen post-monsoon and flooding, while some viruses thrive in warm weather conditions. Moreover, extreme weather fluctuations can also impact the spread of these diseases, including Nipah,'' he said.

"We have a large migrant population in Kerala, coming from different states with endemic diseases not common in Kerala. Many work in the food industry. Improving their living conditions, providing safe water and sanitation, and educating them on hygiene can help prevent the spread of diarrheal diseases like cholera, malaria, and dengue, as well as the spread of viruses like Nipah," Jayadevan said.

Dipu mentioned that the state's improved surveillance system has helped in detecting the presence of viruses.

He said: "The health department has a strong surveillance system, and we investigate the cause when there is a sudden death. While we criticise the state government's lack of preparedness to prevent multiple occurrences of zoonotic diseases, we should also appreciate the efforts taken by the health department to investigate it."

In the past two decades (between 2001 and 2023), India has reported 99 Nipah cases, with Kerala accounting for 28% of the total confirmed cases, including the latest case in Kozhikode. The country has recorded a total of 71 Nipah deaths, with 21 deaths occurring in Kerala.