Face masks have returned to the quiet residential neighbourhood of Melevaram near Farook College in Kozhikode. From the random scooter rider to the health workers huddled outside a family health centre, everyone is wearing them.

The pervasive sense is not fear or anxiety, but caution. The reason is not hard to miss; a 43-year-old resident of the locality has been diagnosed with the deadly Nipah infection.

Abdul Azeez, one of his neighbours, doesn’t seem to be overly worried though. “Health workers have told us that the infection doesn’t rapidly spread like COVID-19. They are visiting the place to monitor the situation every day. But, yes, most of us are wearing face masks while going out as a precautionary measure,” he says.

The infected person has been on ventilator support at the Government Medical College Hospital (MCH), Kozhikode, since June 10. His close family members are already under home quarantine, says Venugopal, a relative who stays nearby.

Contacts under observation

“All his close contacts are now under observation. Lab tests are held if any of them exhibit any symptoms of the infection. So far, all of them have tested negative for the virus. Let’s hope he will survive the ordeal,” he adds.

Health workers attached to the Ramanattukara municipality, in which the locality falls, are not taking any risks, however. A preliminary survey of the 300-odd houses in the area has already been completed. Rajul Koyadeen, medical officer attached to the local body, says a fever survey is going on to find out if any of the residents have had symptoms related to the deadly zoonotic disease. The Health department is also coordinating with the departments of Animal Husbandry and Forest as part of the ‘One Health’ initiative, while taking up containment steps. A team from the Indian Council of Medical Research too visited the area.

Mortality rate of 75%

Their alertness has its own background. Nipah, the virus causing the infection, has a mortality rate of up to 75%. It usually transmits from infected bats and other animals to humans and can also be transmitted directly between people. Fruit bats of the Pteropus species are the natural hosts of the virus. Nipah is also one of the pathogens in the World Health Organisation’s Research and Development Blueprint list of “epidemic threats needing urgent action”.

For the record, this is the fourth time Kozhikode is reporting a Nipah episode. The first official Nipah case in Kerala was from here, in 2018. There have been 10 episodes of the infection in the State till 2025, and 38 cases and 28 deaths so far. After 2018, there was a single case in 2021 and an outbreak in 2023 in Kozhikode. Malappuram, Palakkad, and Ernakulam are the other districts from where cases have been reported.

T.S. Anish, nodal officer of the State government’s Kerala One Health Centre for Nipah Research and Resilience, Kozhikode, highlights some patterns that have emerged from the recurring instances of the infection in the State. The virus is found to have been active in Kerala from April to September. The highest number of cases so far has been in September.

“The fruiting season in the State is around April. Bat foraging happens during the period. Since fruit bats are the natural reservoirs of the virus, the transmission of the infection through fruits can happen in that month,” he observes. The breeding season of the bats is also in the April-May period and then in September. “They become more aggressive and virus shedding — the release of infectious particles into the environment — increases in these months if they are disturbed,” he explains.

Another pattern is the emergence of Perinthalmanna in Malappuram and Kozhikode city as the two most important places in the Nipah calendar. The presence of corporate hospitals and tertiary care government hospitals in this region, where most of the patients are getting admitted, is the reason for the scenario, he claims.

“Most of the cases have been in the six districts that are south of Kannur. The infection is also going southwards from Kozhikode to Malappuram, and then to Palakkad and to Thrissur, possibly because of the shifting of the bat roosts from one place to another,” notes Dr. Anish.

A nationwide survey conducted by the National Institute of Virology, Pune, a couple of years ago had detected Nipah virus antibodies in fruit bats in nine States, including Kerala. A 2021 study had revealed the presence of the virus in fruit bats in “many districts” across the State. Since most of the bat-roosting sites are near human habitats, as per another study by the Kerala Forest Research Institute’s Department of Wildlife Biology, there is an ever-present threat of a spillover. However, the Nipah virus has never been isolated in any fruit samples collected and tested during the outbreaks. Its transmission to humans through fruits bitten by bats remains a scientific possibility. However, every episode of the infection comes with doubts about its recurrence in Kerala, particularly in Kozhikode.

In many other States too

A.S. Anoop Kumar, a critical care specialist at a private hospital in Kozhikode, who played a pivotal role in detecting the Nipah cases in 2018, 2023, 2024, and this year, says the virus is present in many other States across the country. But similar cases are often not diagnosed there because patients with a high index of clinical suspicion may not be getting screened for Nipah in those places. “In Kerala, especially in Kozhikode, a group of doctors and health workers are familiar with its clinical features. So, such patients are regularly examined because of our experience from the 2018 outbreak,” he says.

Dr. Anoop Kumar also notes that the present patient, who was initially admitted to a private hospital, did not have even a fever except during the initial period. “He had low sodium levels and loss of consciousness. The radiologist had reported the MRI scanning results as septic emboli or the changes in the brain following infection in the blood. We suspected Nipah because we are used to seeing such patients. In the clinical screening criteria for Nipah involving his medical history and clinical, radiological and laboratory features, his score was very high,” Dr. Anoop Kumar says.

Since most of the Nipah cases were suspected first in private hospitals and then referred to the public healthcare system, there is also a demand to strengthen the surveillance system in government hospitals as well.

A. Althaf, Professor, Community Medicine, Government Medical College Hospital, Thiruvananthapuram, points out that the recurring Nipah cases in symptomatic patients are also an indication of the need for an “active surveillance” system. He says that if patients with Acute Encephalitis Syndrome (AES) and Acute Respiratory Distress Syndrome (ARDS) are subjected to Nipah-specific tests, more cases could be detected.

Pre-emptive examinations

“At present, the system is responding to the infection only after detecting it. If pre-emptive examinations, also called active surveillance, are enforced, it may lead to more cases. In the first phase, it can be implemented in Kozhikode and Malappuram districts, from where the highest number of such cases have so far been reported,” he suggests.

Health department data show that 56 AES cases and 22 deaths were reported in Kerala in 2023. The next year, the number of cases went up to 122 and there were 37 deaths. In 2025, there were 172 cases and 20 deaths. This year, there have been 62 cases and 12 deaths so far.

Dr. Althaf says that most of these patients were from the northern Kerala districts. Japanese Encephalitis, West Nile fever, rabies infection, and Nipah could lead to AES. “There is a possibility of at least some of the AES cases being Nipah infections in districts where it is frequently being reported,” he feels.

Dr. Anoop Kumar says that the detection of Nipah patients in the initial period could be difficult as their clinical features are similar to those of some other diseases. However, screening those with AES and ARDS will go a long way in detecting more cases, he says. Dr. Althaf and Dr. Anoop Kumar suggest cost-effective tests such as TrueNat instead of RT-PCR tests.

“Through this, more scientific information on the mode of transmission of the infection, the nature of its spreading, and preventive steps can be made available. If the infection is diagnosed early, effective treatment can be ensured and the patient can be saved,” notes Dr. Althaf.

Political controversy

Meanwhile, a political controversy has also erupted with the Opposition alleging lapses in the containment steps. The abrupt transfer of K.J. Reena, incumbent Director of Health Services, for reportedly not officially communicating the lab results of the infected person from the National Institute of Virology, Pune, to Health Minister K. Muraleedharan, also kicked up a row.

Muraleedharan, however, says all efforts are being taken to save the life of the patient. “He was admitted to the hospital in a critical condition. His blood pressure and cholesterol levels seem to be fluctuating. Remdesivir, an antiviral drug not available in India at present, was procured from Bahrain. Along with it, a monoclonal antibody drug and ribavirin, another antiviral drug, are being administered,” he says.

There is maximum vigil and preventive steps are in place to avoid further transmission of the infection at healthcare facilities or between close contacts of the infected person.

The challenge posed by Nipah could be formidable, but the health system in Kerala is trying its best to overcome the crisis by time-tested methods.