The state of Kerala in South India has been at the receiving end of a viral infection allegedly spread by Fruit Bats, to be precise members of the genus Pteropus. They belong to the Family Pteropodidae, the largest bats in the world. Also known as Flying Foxes, Fruit Bats can reach weights of up to 1.5 kg and wingspans of 1.5 m. Unlike most of their smaller cousins, they are herbivores, subsisting on the nectar and ripe fruit borne by trees in tropical and subtropical Africa, Asia and Australia. However, they are not totally harmless. Members of the Fruit Bat group are reservoirs for some really nasty viruses that can infect and kill human beings. Some of the more well known examples are the Ebola Virus (that killed as many as 11,300 people in West Africa between 2013-2016) and the Marburg Virus (that killed around 200 people in Angola between 2004-2005). It seems that many of the host bats are not affected in any way by the viruses inside their body.
Other less known viruses harboured by them are the Lyssavirus found in Black Fruit Bats (Pteropus alecto) of Australia-New Guinea, and the Nipah Virus found in Large Fruit Bats (Petropus vampyrus) of Southeast Asia. It is the Nipah Virus that has created panic in India. The whole thing began with the death of at least 12 people, including a nurse in Kerala’s Kozhikode District. The Nipah Virus can spread between human beings or from animals (like bats and pigs carrying the virus) to human beings. Transmission requires physical proximity or contact with the animals’ feces, urine or saliva. The first time a Nipah outbreak killed people was in Malaysia and Singapore in 1999. It was named after a village – Sungai Nipah, in Malaysia. Given below is a brief description of the Virus by the United States’ Centers for Disease Control and Prevention (CDC):
Nipah virus (NiV) is a member of the family Paramyxoviridae, genus Henipavirus. NiV was initially isolated and identified in 1999 during an outbreak of encephalitis and respiratory illness among pig farmers and people with close contact with pigs in Malaysia and Singapore. Its name originated from Sungai Nipah, a village in the Malaysian Peninsula where pig farmers became ill with encephalitis. Given the relatedness of NiV to Hendra virus, bat species were quickly singled out for investigation and flying foxes of the genus Pteropus were subsequently identified as the reservoir for NiV.
In the 1999 outbreak, Nipah virus caused a relatively mild disease in pigs, but nearly 300 human cases with over 100 deaths were reported. In order to stop the outbreak, more than a million pigs were euthanized, causing tremendous trade loss for Malaysia. Since this outbreak, no subsequent cases (in neither swine nor human) have been reported in either Malaysia or Singapore.
In 2001, NiV was again identified as the causative agent in an outbreak of human disease occurring in Bangladesh. Genetic sequencing confirmed this virus as Nipah virus, but a strain different from the one identified in 1999. In the same year, another outbreak was identified retrospectively in Siliguri, India with reports of person-to-person transmission in hospital settings (nosocomial transmission). Unlike the Malaysian NiV outbreak, outbreaks occur almost annually in Bangladesh and have been reported several times in India.
The needle of suspicion turned towards the Indian Fruit Bats (Pteropus giganteus) in the Kozhikode outbreak for two reasons. In 2001, there was a Nipah outbreak in Siliguri (in the state of West Bengal), and Meherpur (across the border in Bangladesh). Biologists found proof of the Virus in Indian Fruit Bats. In Kozhikode, dead bats were found in a well on the victims’ family property. This rang alarm bells across the country, and led to speculation of a ‘virus spillover’ from Fruit Bats to humans. There were several reports linking bats with the outbreak. Some journalists linked it to widespread deforestation, with loss of natural habitat forcing the flying mammals to seek shelter near human settlements.
However, the speculation ignored one crucial fact – the bats found in the well were not Fruit Bats. They were of a smaller, insectivorous species. Analysis of samples by India’s National Institute of High Security Animal Diseases has also returned negative results for the presence of Nipah Virus in the dead bats. This means that there might be some other species of mammal acting as the reservoir. Nothing can be said for sure till further investigations take place, and solid proof is obtained. However, the panic continues unabated. Homes have been abandoned by alarmed residents of Kozhikode and Mallapuram Districts in Kerala. Tourists have cancelled their hotel bookings and flight tickets, hitting the economy hard.
The fear is not completely baseless. Nipah Virus causes an infection with no known cure. Patients have to be isolated and given intensive care. The mortality rate can be high. Infected individuals show signs of encephalitis (inflammation of the brain), fever and headache, drowsiness, disorientation and mental confusion within 5 to 14 days. This can rapidly escalate to coma (within another 24 to 48 hours), and death. Those who survive may suffer permanent brain damage, characterized by convulsions and personality changes. As it is, Indians are a very gullible and panicky lot. Alarming SMSes, WhatsApp messages and FB posts are painting Fruit Bats as the villains of the piece. Very often, they carry images of the big-eyed critters feasting on their favorite fruits.
While lacking proof, these images do highlight an interesting aspect of the Fruit Bats’ role in transmitting diseases. It seems that their love for ripe fruits and sugary plant secretions can indeed kill humans. Studies of the outbreaks in West Bengal and Bangladesh found that Indian Fruit Bats (Pteropus giganteus) love the sap of Date Palms (Phoenix dactylifera). And while trying to get to it, they would contaminate the pots used by Bengali tappers (people who collect date palm sap) with their saliva or urine. These bodily secretions, loaded with the Virus, then channeled the pathogen into people consuming the sap. A similar ‘spillover’ could have taken place in Kerala. But nobody knows for sure.
Image Attribution: The image above, sourced from Wikimedia Commons, shows a Black Fruit Bat (Pteropus alecto) feeding on a Palm in in Brisbane, Queensland, Australia. Their larger relative, the Indian Fruit Bat (Pteropus giganteus) has a similar affinity for Date Palm sap which might be the cause behind Nipah outbreaks in South Asia. The photograph was uploaded by Andrew Mercer.
- Centers for Disease Control and Prevention (USA)
- Nipah virus outbreak in India: What you need to know (Deutsche Welle, dated May 22, 2018)
- Nipah Virus That Killed 12 In Kerala May Not Be Linked To Bats: 10 Points (NDTV, dated May 26, 2018)
- What is the connection between fruit bats and Nipah virus? (The Hindu, dated May 26, 2018)
- Nipah virus in Kerala: Don’t blame the bats, they aren’t the key carriers (Business Standard, dated May 26, 2018)