Humans create hotspots where bats can transmit zoonotic diseases

As the habitats of humans and animals move closer together, with large areas of forest to make way for buildings and farmland, scientists fear that zoonoses such as COVID-19 will develop more and more. According to some researchers, regions where such drastic shifts have occurred and where large numbers of bats live could be the starting point for the next coronavirus pandemic.

A group of scientists recently identified where such outbreaks occur. Conditions in these ‘hotspots’ are likely to be favorable for SARS-related coronaviruses to outgrow. The researchers looked for sites where there are many Asian bats, the animals with the greatest diversity of coronaviruses, and where there is also a lot of building and farming and the forest has become fragmented.

By identifying potential hotspots, scientists can “help us think of ways we can reduce the likelihood of another COVID-19 pandemic,” said David Heymann, one of the researchers involved in infectious diseases, at Massey University in New Zealand.

Using those hotspot criteria, the researchers analyzed more than 28.5 million square kilometers of land with a dense population of Asian horseshoe bats. These animals live in the tropics and temperate regions and get their name from their large, bow-shaped nose. The researchers looked at more than ten thousand sites in total.

They found that the risk was greater in certain areas of China and that some areas in other parts of Asia, such as Japan, Thailand, the Philippines and Europe, could become hot spots.

Their research was published in May in the scientific journal nature foods.

The researchers note that they cannot directly link changes in land use to the spread of SARS-CoV-2 and the emergence of COVID-19. But according to them, this possibility exists and more attention should be paid to the way humans disrupt the habitat of bats.

“We know that the risk of cross-contamination between species increases as there is more contact between species.” This includes humans and bats, Hyman explains. The analysis identifies “areas where such conditions may occur”.

A potential tool to prevent the spread of disease

A previous study showed that the risk of an Ebola outbreak is higher in areas where forests have become fragmented. For this reason, this has been used as a criterion for identifying hotspots for the potential emergence of coronavirus epidemics.

Forest fragmentation is not in itself a cause of disease spread. “It comes down to what this fragmentation means,” said University of Washington ecologist Chelsea Wood, who was not involved in the new research. “When there is a fragmented habitat, there is more contact between the people and the animals that live in that area.” As forests become fragmented, “you create more and more boundaries between human and animal habitats, and with them more and more opportunities for interaction,” she says.

In the latest study, researchers found the largest number of hotspots in China, places where “forest fragmentation, animal husbandry, and human habitation converge,” says Nicolas Galli, a PhD researcher at Italy’s Politecnico di Milano who was involved in the study. The researchers also found that there are areas in Japan, the Philippines, and Western Europe (including northern Italy, Spain and Portugal) that could become hot spots with increased human settlement, livestock farming, or increased forest fragmentation.

“As a European, I think there is a bias that zoonotic infections are only dangerous in areas far from us,” Galle said. He adds that the study results didn’t surprise him, but they “make a little difference in our perspective.”

The researchers stress that the map is based on the hypothesis that “increased livestock farming, forest fragmentation, and human settlement lead to a greater risk of transmission of zoonoses,” Wood said. She says the map is not proof that this is really the case.

Colin Carlson, a biologist at Georgetown University, agrees. The map does not indicate that land use change was the cause of COVID-19. We don’t know that. We still don’t know what a tank is. We still don’t know if there is an intermediate host.”

Nevertheless, the researchers hope that the map will be a valuable tool in the fight against the disease.

“These findings can help governments develop disease control plans,” said Maria Cristina Rulli, professor of water and food safety at Politecnico di Milano. The research findings show where extra precautions should be taken against the possibility of disease transmission and where nature should be restored to be on the safe side.

Hyman adds that areas that have been identified as potential hotspots “should preemptively halt policies that increase risk factors.”

Bats carry diseases

It is still unknown how the first patient contracted SARS-CoV-2, the virus that causes COVID-19. But the widely accepted theory among scientists is that the new coronavirus originated in bats and was transmitted to humans, either directly or through an intermediate host.

“Bats remarkably serve as a reservoir of viruses,” Wood said.

For example, they can be carriers of rabies, a dangerous viral disease that affects the human nervous system. Some species can easily carry the Nipah virus, which causes respiratory infections in humans, and Ebola, a disease that has killed thousands of people worldwide.

Wood said scientists don’t know why these winged animals often carry viruses, or why they don’t get sick themselves “while carrying pathogens that are extremely dangerous to other mammals.” What they do know is that bat viruses can spread to other animals, including humans, often with dire consequences: Nipah can spread when people drink palm juice contaminated with bat droppings, and researchers say at least one Ebola outbreak started after humans. . Bats that hunt, catch, or eat animals.

And while it may seem strange for people in some parts of the world to have direct and intimate contact with bats, in other parts of the world it’s normal to live near bats, Wood said. In some countries, bats are “as common as squirrels in the United States.”

Children who play near a tree with a bat’s nest can take the excrement home – or put it directly in their nose or mouth. In some countries, bats are hunted and eaten by animals.

Viruses can also be transmitted from bats to humans through an intermediate host – another animal that transmits the virus from bats to humans. This may have happened in some Ebola outbreaks.

“The scary thing about these zoonotic viruses is that there’s transmission all the time,” Wood said. But the most dangerous and best monitored viruses are those that can spread between humans. “This is a huge achievement for a virus that used to pass between bats and other mammals,” she says. “COVID-19 is a good example of that.”

This article was originally published in English at NationalGeographic.com