The health team, probing the source of Nipah infection in 14-year-old boy from Malappuram who died on Sunday, has learnt that the boy may have consumed a wild hog plum (Ambazhanga in Malayalam) from an area which could be a foraging site of fruit-eating bats. The initial hypothesis is that the hog plum infested by the contact of bats could be the source of infection.

The boy along with four of his friends went to a spot, approximately 2km away from his home, on July 6. They walked along the paddy fields and reached a site with trees and canal nearby. The disease investigation team also has information that the boys had a bath in the canal and they consumed hog plums of a wild variety from the area.

The boys remembered the day (July 6, Saturday) clearly as it was a holiday. The boy knew the path to this spot and was accompanied by three of his friends from the neighbourhood and one another boy. The incubation period of the virus is 13-14 days.

Within a week of being exposed to the virus, the boy developed symptoms and was first taken to a private hospital and when his condition worsened he was referred to another hospital on July 15 where he was admitted to paediatric ICU till July 19 and then he was shifted to another private hospital on July 19.

Although other boys also ate the fruit, they were not infected and none of them have symptoms either and are past the incubation period. The team is learnt to have tracked the path to the spot and affirmed the presence of bats in the area.

Large fruit bats of Pteropus genus are the natural reservoir of Nipah virus (NiV). Pigs are identified as intermediate hosts. In a study conducted during the Nipah outbreak in 2018, the high positivity of NiV was detected in bat throat swabs, and showed persistence of virus for a couple of hours on contaminated fruits, which enhance the chances of human infection.

NiV positivity was identified in bats from North Eastern region states and Kerala, according to the document prepared by the health department. Nipah virus can remain alive on fruit surfaces for two hours to over 30 hours, depending on temperature and weather conditions, notes an article in the Nature.

The place where the boys had frequented will be monitored to confirm the presence of bats in the area and establish the source of infection. An official said that the roosting sites of bats are different from the foraging sites and this particular spot has been identified as a foraging site due to the presence of fruit-bearing trees. Investigations of Nipah outbreaks in Bangladesh had accounted consumption of fresh date palm sap as the reason for bat to human transmission.