The Nipah fever outbreak, which claimed 21 lives in Kerala last year, may have emanated from a bat species called the Indian flying fox, but there are 10 other bat species in India that can potentially harbour the virus, a study by Indian and US scientists has shown.
The study, which appeared in the journal PLoS Neglected Tropical Diseases on Friday, is significant from the point of view of disease surveillance. Globally, the health community is in the dark when it comes to diseases caused by pathogens hosted by animals.
The highly-fatal Nipah virus is no exception. Though the Nipah fever surfaced once again in Kerala this year, the infection has been contained so far, without any known mortality.
Humans get infected with Nipah virus when they are exposed to the body fluids of infected bats. Eating fruit or drinking date palm sap that has been contaminated by bats has been flagged as a transmission pathway.
Once infected, people can spread the virus directly to other people, sparking an outbreak. Domestic pigs are also bridging hosts that can infect people. The mortality associated with Nipah is extremely high as there is no effective drug against the infection nor is there a vaccine.
The scientists led by Raina Plowright, a disease ecologist at the Montana State University and Barbara Han of the Cary Institute of Ecosystem Studies in Millbrook in the US, used machine learning, a form of artificial intelligence, to identify which of these nocturnal mammals can host the deadly virus.
To do so, the scientists looked at the traits of bat species known to carry the virus globally, and used them to make predictions about additional bat species in India that have the potential to carry the virus and transmit it to people.
The sole Indian scientist involved in the study was PO Nameer, a researcher with Centre for Wildlife Studies at the Kerala Agricultural University.
The scientists catalogued as many as 48 different traits of these species that act as vector. The traits identified include foraging methods, diet, migration behaviours, geographic ranges and reproduction. They also looked at the environmental conditions in which reported animal-to-human transmission occurred.
India is home to an estimated 112 bat species. Just 31 of these species have been sampled for Nipah virus, with 11 found to have antibodies that signal host potential. Among these are cave nectar bat, greater and lesser short-nosed fruit bat, Anderson's leaf-nosed bat, Great Himalayan leaf-nosed bat and Leschenault's rousette.
“Given the role bats play in transmitting viruses infectious to people, investment in understanding these animals has been low. The last comprehensive and systematic taxonomic study on the bats in India was conducted more than a century ago,” said Plowright, in a statement.
According to Plowright, their model was successful in identifying Nipah hosts, demonstrating that this method could serve as a powerful tool in guiding surveillance for Nipah and other disease systems.
The authors said that their predictions must be combined with local knowledge on bat ecology — including distribution, abundance and proximity to humans — to design sampling plans that can effectively identify bat hosts that pose a risk to humans. “This work provides a list of species to guide early surveillance and should not be taken as a definitive list of reservoirs,” they added.
“Surveilling high-risk bat populations can provide early warning for veterinarians and public health authorities to take preventative measures needed to pre-empt an outbreak. Identifying which species harbour disease is an important first step in surveillance planning. We also need to prioritize research on which virus strains pose the greatest risk to people, said Han.