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A new study shows that rats and bats harboring pandemic pathogens like Covid-19 increase in damaged ecosystems.
Human destruction of natural ecosystems increases the number of rats, bats and other animals that harbor diseases that can lead to pandemics such as Covid-19, according to a comprehensive analysis.
The research evaluated nearly 7,000 animal communities on six continents and found that converting wild places to farmland or settlements often eliminates larger species. It found that the damage benefits smaller, more adaptable creatures that also carry most of the pathogens that can be passed on to humans.
The assessment found that populations of animals harboring what are known as zoonotic diseases were up to 2.5 times larger in degraded locations, and that the proportion of species carrying these pathogens increased by up to 70% compared to undamaged ecosystems. .
Human populations are increasingly affected by diseases that originate in wild animals, such as the HIV virus, Zika, Sars and Nipah. Since the coronavirus pandemic began, there have been a number of warnings from the UN and WHO that the world must address the cause of these outbreaks, the destruction of nature, and not just the economic and health symptoms.
In June, experts said the Covid-19 pandemic was an "SOS signal for human enterprise," while in April the world's leading biodiversity experts said even more outbreaks of deadly diseases are likely to occur unless that nature is protected.
The new analysis is the first to show how the demolition of wild places, as the world's population and consumption grow, leads to changes in animal populations that increase the risk of disease outbreaks. Research shows that disease surveillance and medical care must be increased in areas where nature is being ravaged, the scientists said.
“As people go in and, for example, turn a forest into farmland, what they do inadvertently is that they are more likely to be in contact with a disease-carrying animal,” said David Redding of the ZSL Institute. of Zoology in London, who was one of the members of the research team. The work is published in the journal Nature.
Redding said the costs of the disease were not taken into account when deciding to convert natural ecosystems: "So you have to spend a lot more money on hospitals and treatments." A recent report estimated that only 2% of the costs of the Covid-19 crisis would be needed to help prevent future pandemics for a decade.
"The Covid-19 pandemic has awakened the world to the threat that zoonotic diseases pose to humans," said Richard Ostfeld, from the Cary Institute for Ecosystem Studies, USA, and Felicia Keesing at Bard College, USA. ., in a comment in Nature.
"With this recognition has come a widespread misperception that the wild is the greatest source of zoonotic disease," they said. “This research offers an important correction: the greatest zoonotic threats arise where natural areas have been converted to croplands, pastures and urban areas. The patterns that the researchers detected were surprising. "
The reason species such as rodents and bats simultaneously thrive in human-damaged ecosystems and also host most pathogens is probably because they are small, mobile, adaptable, and produce lots of offspring quickly.
"The latest example is the brown rat," Redding said. These fast-living species have an evolutionary strategy that favors large numbers of offspring before a high survival rate for each, meaning that they invest relatively little in their immune systems. "In other words, creatures that have rat-like life histories appear to be more tolerant of infections than other creatures," Ostfeld and Keesing said.
"In contrast, an elephant has a calf every two years," Redding said. "You have to make sure that the offspring survive, so that they are born with a very strong and adaptive immune system."
The analysis found that small perching birds are also disease hosts that do well in habitats that are impacted by human activities. These birds can be reservoirs for diseases such as West Nile virus and a type of chikungunya virus.
Humans have already affected more than half of the habitable land on Earth. Professor Kate Jones from University College London, and also part of the research team, said: “As agricultural and urban lands are predicted to continue to expand in the coming decades, we should strengthen disease surveillance and health care provision in those areas that are experiencing a lot of disturbances on the land, as it is increasingly likely that they have animals that can harbor harmful pathogens.