Diseases transmitted from animals to humans have caused some of the most devastating epidemics in human history.
Understanding bat biology could reduce the risk of disease spreading in the first place, researchers said at a Cornell University webinar on June 26.
Bats are not the only animals that carry zoonotic diseases. But these are notable cases, and not just because they are a possible source of COVID-19.
First, bats make up 20 percent of all mammals, so it’s no surprise bats carry a lot of viruses, says Raina Plowright, a disease ecologist at Cornell University’s School of Veterinary Medicine.
In addition, bats have many traits that allow them to withstand viruses that bring down humans.
Bats are particularly good at controlling inflammation. An uncontrolled inflammatory response by the immune system is responsible for deaths from COVID-19 and Ebola, researchers said. Dean ReaderProfessor of Biology, Bucknell University.
In addition, bats are the only flying mammals and the only animals whose bodies are strained by both flying and feeding.
“So bats have huge energy needs and voracious appetites,” says Rieder.
Due to this enormous energy requirement, bats are more likely to become stressed when their food sources are limited or their habitat is disturbed. And stressed bats excrete large amounts of virus.
Of course, the presence of pathogens in the environment does not mean that pandemics or human infections are inevitable.
For a pathogen to pass from an animal to a human, the host animal must be infected, territorial with humans, and excrete the pathogen, Plowright said.
Microbes also require mechanisms for human exposure. Often this is another animal, such as a foraging pig that has come into contact with infected bat guano.
Even then, the pathogen must be able to bind to receptors on human cells and evade the body’s immune system.
Spreading among humans requires a further set of circumstances.
Pathogens must multiply and be effectively transmitted within the human body. Respiratory diseases like COVID-19 are easily spread by coughing and sneezing, but rabies is not contagious from person to person, Plowright said.
A jump from an animal to a human is called a spillover. Not everyone is convinced that it can be stopped. But Plowright is optimistic and believes there is value in pursuing that goal.
Most of the research on emerging infectious diseases has focused on early detection and control of the spread of infections such as vaccines. These tools are important, she said, but unlike contagion prevention, they are difficult to deploy quickly and fairly.
“This is a stepping stone for the pandemic, and if we can stop this, we can stop pretty much anything else,” she said.
Professor Plowright came up with an idea for combating the spill by studying large nectar-sucking bats in the subtropics of Australia.
These bats are carriers of the Hendra virus and can jump from bats to horses to humans. According to the World Health Organization, 80% of infected horses and 60% of those infected die, but only seven human cases have been reported, Plowright said.
Infected Australian bats travel long distances in large groups, feeding and pollinating native bush.
However, since most of their winter habitat has been destroyed, they have moved to cities and farms where they eat their fruit. In such less-than-ideal conditions, bats shed large amounts of virus.
On rare occasions, when the remaining habitat blooms in winter, bats return to the area, but no disease spread is detected.
These findings point to a low-tech disease prevention strategy that restores the original habitats where bats feed and sleep.
In addition to helping bats, Plowright said it could help expand habitat for koalas and a variety of migratory birds, as well as promote planting trees to combat climate change.
These basic strategies may also apply to disease-carrying species other than bats, and indeed different bat species should have different strategies.
Various types of bats feed on insects, nectar and other small animals. Some roost in caves, others in trees and buildings, said Teague O’Mara, director of conservation evidence for Bat Conservation International.
Humans could also find ways to reduce commercial conflict with bats without destroying vital industries for rural communities.
Guano harvesting and cave tourism may be limited to periods when bats are not roosting or hibernating. O’Mara said protective gear could keep harvesters safe.
Hunting bats for food is of particular concern because it brings humans closer to bats, although it plays a role in some local cultures.
In Nigeria, hunters often set up large nets at cave entrances to attract bats into the cave. This process allows him to bag 4,000 bats at a time, stressing the bats that were not caught.
“It can’t be sustainable,” says Ilolo Tansi, co-founder of the small mammal conservation group in the country.
In areas where hunters catch bats for food, Tansi’s group provides an alternative source of protein and income.
