Researchers have found that hungry bats are more prone to transmit viruses to people and other animals. This study may help determine when future outbreaks will happen.
In a thorough investigation of Australia’s flying foxes, scientists discovered that the megabats,’ which had wingspans up to three feet, shed far more virus when they were famished. At the same time, their pursuit of food brought them closer to people and animals.
This confluence created the conditions for an increase in spillover incidents, in which infections spread to humans or other animals. Understanding the causes of these outbreaks may make it possible to foresee when they will occur and prevent them before they become epidemics.
The Hendra virus, an uncommon respiratory and neurological condition carried by bats was the subject of the investigation. The immune systems of the flying animals are “supercharged,” enabling them to cohabit with several harmful infections, such as the Nipah virus, Marburg, and Sars.
However, Hendra kills about 75% of the horses that catch it. Foamy nasal discharge, fever, wheezing, and frantic behaviors like drinking water nonstop or hitting themselves against the walls are some symptoms.
The illness, which was initially discovered in Australia in 1994, can also affect people. Two humans contracted the virus from the horses during the initial outbreak: a stable hand who recovered and a 49-year-old trained horse who did not. Since then, Hendra has infected seven people, leaving four dead, and has spread from bats to horses in about 60 distinct spillover incidents.
For the past 25 years, researchers in Australia and the United States have been gathering data to identify the precise causes of these spillovers. The group discovered that clusters of Hendra outbreaks occurred after the flying foxes experienced severe food shortages in two seminal papers that were published in Ecology Letters and Nature.
The normally nocturnal bats rely significantly on the nectar of eucalyptus blossoms, and when those flowers are in bloom, they flock to trees in enormous “lively roosts.” There were no overflow events noted in the years when these flowers were in bloom.
Nutritionally stressed: However, as a result of deforestation and climate change, trees are growing fewer and fewer blossoms. Flying foxes are now compelled to move farther into areas where people live in order to locate food, where they come into closer contact with horses.
The probability of an outbreak was further increased after the researchers sampled the bats and discovered that they had greater frequencies of the Hendra virus, particularly in the winters following a nectar shortage caused by climate change. This is probably due to the starving, freed bats’ lack of energy to sustain an immune response that controls the viruses.
“We can assume that across mammals that animals that are nutritionally stressed are less able to control viruses and are therefore more likely to shed viruses,” Prof Raina Plowright, an infectious disease ecologist at Cornell University, told the Telegraph.
She added that this likely applies to other bat viruses, too – including Nipah, a disease with a fatality rate of up to 70 percent.
“Strategies that make sure that animals have enough to eat, have enough habit so they are not stressed and so they can move through their environment without having to overlap with humans, all contribute to reducing spillover risk,” Prof Plowright said.
Health authorities were able to warn horse owners of the dangers and ensure that their animals have immunized thanks to the scientists’ accurate predictions of when the Hendra virus will spread from bats to horses up to two years in advance.
“In general, strategies that make sure that animals have enough to eat, have enough habit so they are not stressed and so they can move through their environment without having to overlap with humans, all contribute to reducing spillover risk,” said Prof Plowright.
However, she cautioned that research on the ecology of the disease’s reservoir host, such as bats, is scarce.
“We usually just focus on the virus, and usually only after it is spreading in the human population,” she said. “We rarely work backwards to figure out where the virus came from and why it emerged from a wild species into humans.
“If we understand the ecology of the reservoir hosts – the food they need at different times of years and when that food is available or removed then we can study those times and places where all of the stressors align,” Prof Plowright added.
The discoveries come as more information comes to light that might enable researchers to follow the evolution of Sars-Cov-2 before it entered the human population.
Researchers presented fresh findings from an investigation that indicated that bat coronaviruses and Sars-Cov-2 shared an ancestor as recently as 2016 at the One Health Congress earlier this month in Singapore.
“We need to sequence the entire viral genome of these circulating bat viruses, not just tiny pieces of it [because they mutate and recombine constantly,” Prof Joel Wertheim, an evolutionary biologist at the University of California San Diego and co-author of the analysis, told The Telegraph.
“We risk missing the crucial bits that reveal the pre-history of Sars-CoV-2 if we don’t sequence small fragments of these bat virus genomes,” the study authors write.
