Six days after his death, Nipah infection was confirmed in a 24-year-old deceased patient in Kerala’s Malappuram district on September 15. The deadly zoonotic disease has claimed 22 lives in the state since it was reported first in 2018. Though Kerala has achieved significant progress in reducing the case fatalities, it is still puzzled over one major problem – the mode of transmission from bats to humans.
Studies conducted on index patients in the outbreaks, point to the possibility of consumption of fruits contaminated by Nipah Virus (NiV). After every outbreak, there is a decline in the sale of fruits in Kerala. However, there is no proof that contaminated fruit causes the transmission. Scientists and health experts are yet to zero in on the reason for spillover.
In the two recent deaths – a 14-year-old boy on July 21 and a 24-year-old man on September 9 in Malappuram – preliminary findings point to the possibility of consuming potentially contaminated fruits. According to relatives, the 14-year-old had a hog plum, locally known as Ambazhanga, and the recent victim is said to have consumed unwashed Bilimbi fruit (Irumban puli). Though consumption of contaminated fruits was seen as a possible cause of transmission, scientists could not trace the presence of NiV in samples of such fruits in the area.
Dr Anish TS, nodal officer at One Health Centre for Nipah Research in Kozhikode said that genomic sequencing of NiV from affected persons matched with that of bats in the area. “That shows that the virus was transmitted from bats to humans. The presence of the virus, however, was not found in the samples of fruits collected in the area,” he said. According to him, NiV was found to survive on fruits and beverages in laboratory experiments. The experiment showed the possibility of transmission through contaminated fruits and palm. However, failure to confirm the presence of NiV in the natural environment remains a concern.
According to Dr Anish, there is a lacuna in identifying the exact mode of transmission from bats to humans. He added that it was not a Kerala-specific issue. “In Malaysia, (where the first outbreak was reported in 1999), the infection was caused by contact with pigs. As per assumption, pigs might have infected from contaminated fruits or secretions from nearby bat roosts. In Bangladesh, consumption of date palm sap was considered a possible cause of transmission. However, in all these cases, the presence of the virus was not detected in fruits or beverages in their natural environment,” he said.
The presence of Nipah virus and antibodies was confirmed in bat roosts in Kerala. The Health Department has also analysed a direct link between the increased presence of virus in bats and Nipah outbreaks. “The presence of the virus is found to increase from February and reach its peak by September. The previous outbreak reported in 2023 was in August and September,” Dr Anish said. Six persons were infected, and two deaths occurred in Kozhikode district then.
The Health Department is also probing the possibilities of an intermediate host, most likely an animal that preys on or attacks bats. Studies are also being held on the chances of airborne transmissions near bat roosting sites.
Malappuram District Medical Officer Dr R Renuka said that no positive cases were reported in the district after the deaths in July and September. She said that the quarantine period of the remaining persons in the contact list would end by September 31.
Following the outbreak of zoonotic diseases like Nipah, Kerala has started emphasising on ‘One Health’, which, according to the World Health Organisation, is an integrated, unifying approach to balance and optimise the health of people, animals, and the environment. One Health institutes were established in Thiruvananthapuram and Kozhikode for research, surveillance, and early detection of outbreaks.