Humans create hot spots where bats can transmit zoonoses

As the habitats of humans and animals come closer, with vast swathes of forest to make way for buildings and farmland, scientists fear that zoonoses such as COVID-19 will increasingly develop. According to some researchers, areas where such drastic transformations have taken place and where large bat populations live could be the starting point of the next coronavirus pandemic.

A group of scientists recently mapped where such outbreaks could take place. Conditions in these “hot spots” are likely to be favorable for SARS-linked coronaviruses to jump. The researchers looked for places where there are many Asian horseshoe bats, the animals with the greatest diversity of coronaviruses, and where there is also a lot of construction and farming and where the forest has grown. fragmented.

By identifying potential hot spots, scientists can “help think about ways to reduce the risk of another COVID-19 pandemic,” says infectious disease professor David Hayman from Massey University in New Zealand, one of the researchers involved.

Using these hotspot criteria, the researchers analyzed more than 28.5 million square kilometers of land with a dense population of Asian bats. These animals live in tropical and temperate regions and get their name from their large, arched noses. The researchers looked at over ten thousand locations in total.

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

Their research was published in May in the scientific journal Natural food.

The researchers note that they cannot directly link land use changes to the spread of SARS-CoV-2 and the emergence of COVID-19. But they say the possibility exists and more attention should be paid to how humans disturb bat habitat.

“We know that the risk of interspecies contamination increases the more there is contact between species.” And that includes humans and bats, says Hayman. The analysis identifies “areas where such conditions can occur”.

A potential tool for preventing the spread of disease

of Previous search have already shown that the risk of an Ebola epidemic is greater in areas where forests have become fragmented. For this reason, it was used as a criterion for identifying hot spots for the possible emergence of coronavirus outbreaks.

The fragmentation of forests in itself is not a cause of the spread of disease. “It’s about what this fragmentation means,” said Chelsea Wood, a University of Washington environmentalist, 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 are creating more and more boundaries between the habitats of humans and animals, and with them more and more opportunities for interaction,” she says.

In the recent study, the researchers found the greatest number of hotspots in China, places where “the fragmentation of forests, ranching and human habitation” converge, explains Nikolas Galli, doctoral student at Politecnico di Milano in Italy. who participated 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 potentially become hotspots as human settlements , animal husbandry or forest fragmentation is increasing, Galli said.

“As a European, I think there is a prejudice that zoonotic infections are only a risk in areas far from us,” said Galli. He adds that the results of the study did not surprise him, but that they “definitely qualify our perspective”.

The researchers point out that the map is based on the hypothesis “that an increase in animal husbandry, forest fragmentation and human habitation leads to an increased risk of zoonotic transmission,” Wood said. The card is not proof that this is really the case, she said.

Biologist Colin Carlson from Georgetown University agrees. “The map does not say that the land use change was the cause of COVID-19. We do not know it. We still don’t know what the reservoir was. We still don’t know if there was an intermediate host.

Nonetheless, researchers hope the card can be a valuable tool in the fight against the disease.

“These findings could help governments develop disease surveillance plans,” said one of them, Maria Cristina Rulli, professor of water and food safety at Politecnico di Milano. Research results show where extra care needs to be taken against possible disease transmission and where nature needs to be restored to be on the safe side.

Hayman adds that areas identified as potential hot spots “must” preventively stop policies that increase risk factors. “

Bats as vectors of disease

It is still unclear how the first patient got infected with SARS-CoV-2, the virus that causes COVID-19. But a widely accepted theory among scientists is that the new coronavirus originates from bats and has been transmitted to humans, either directly or through an intermediate host.

“Bats do remarkably well as a reservoir of virus,” said Wood.

This is how they can be a carrier of rabies, a dangerous viral disease that affects the human nervous system. Some species can do this without any problem Carry the Nipah virus, which causes respiratory infections in humans and Ebola, a disease that affects the world thousands of people died.

Scientists don’t know why these winged animals are so often carriers of viruses, or how they don’t get sick themselves “while carrying pathogens that are extremely dangerous to other mammals,” Wood said. What they do know is that bat viruses can spread to other animals, including humans, with often dire consequences: Nipah can spread when people drink date palm juice which is contaminated with bat droppings and researchers say at least one Ebola outbreak started after people hunted bats, caught or ate animals.

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

Children playing near a tree with a bat’s nest can take leftover droppings into the house – or put it right into their noses or mouths. In some countries bats are hunted and animals are eaten.

Viruses can also pass from bats to humans through an intermediate host, another animal that transmits the virus from bats to humans. This probably happened at some Ebola epidemics.

“The scary thing about these zoonotic viruses is that there is transmission all the time,” said Wood. But the most dangerous viruses, which are also the best monitored, are those that can spread between people. “That’s quite a feat for a virus that’s used to spreading between bats and other mammals,” she says. “COVID-19 is a good example. “

This article originally appeared in English on NationalGeographic.com