As humans degrade the Earth’s environment, we have created a world in which diseases may be increasingly likely to fester and multiply.
Creatures that spread infections, such as mosquitoes and ticks, thrive on a planet warmed by a blanket of fossil fuel emissions. When pollution, hunting, or development drive rare organisms to extinction, parasites proliferate because they have evolved to attack more abundant species.
And then there is the damage caused when humans introduce non-native plants and animals or chemicals like herbicides and fungicides into fragile ecosystems. According to a study published Wednesday in the journal Nature, this exacerbates the loss of biodiversity and makes surviving populations more vulnerable to disease.
The researchers said this study is the first to look at how this variety of environmental problems can exacerbate disease risks. It combined hundreds of studies and thousands of observations of all types of creatures – humans and other mammals, fish, reptiles, amphibians, worms and arthropods – and all types of pathogens, such as viruses, bacteria and fungi.
The analysis reinforced the conclusions of much of that research: that a warmer world with devastated ecosystems is more hospitable to many parasites, and less hospitable to humans and other living beings.
The connection appeared with all types of infections and their hosts, suggesting that as the planet continues to warm and humans continue to alter nature, the increase in the spread of diseases “will be constant and widespread,” said Jason Rohr, professor of biological sciences at the University of Notre Dame and one of the authors of the study. He added that the relationship was as clear with humans as with fauna and flora.
“And this despite all the efforts we make to control and prevent diseases,” said Rohr.
The study suggested that if diseases proliferate in the animal world, it could increase the likelihood of “contagion” cases that expose humans to new pathogens, the likely origin of Covid-19 and one of the feared consequences of the spread of H5N1 avian flu.
“It could mean that by changing the environment, we increase the risks of future pandemics,” Rohr said.
As bleak as the results may seem, they underscore that actions to protect the planet can also serve to improve health, the researchers said.
“This adds to a long list of reasons why we should quickly move away from fossil fuels and try to mitigate the effects of climate change,” said Felicia Keesing, a professor at Bard College who was not involved in the study but whose research focuses on on biodiversity and disease risks.
The study used observations of disease outcomes affecting a wide variety of parasites that infect a spectrum of hosts around the world. The observations also included information on a range of human influences on the environment: changes in biodiversity, chemical pollution, climate change, habitat loss or change, and introduction of non-native species.
Biodiversity presents a natural gradient across the planet, with the greatest number of species near the equator and at moderate elevations. The researchers measured the effect of human-caused biodiversity loss on disease by comparing observations of infections around the world with the average prevalence of disease at different levels of biodiversity along that natural gradient. In nature, the reduction of biodiversity is associated with a decrease in diseases.
But when humans cause biodiversity losses, diseases increase. The researchers found that levels of disease and mortality in environments affected by such human-caused declines in life were nearly nine times worse than disease outcomes expected across Earth’s natural biodiversity gradient.
According to Rohr, this is probably because the loss of rare creatures makes it easier for pathogens to find the more abundant species they have evolved to use as hosts.
The researchers also found that climate change and the introduction of non-native species have significant links to worsening disease spread, although not as strong as the effect of biodiversity loss.
The analysis found a human-influenced variable that actually decreased disease risks: habitat loss. According to Rohr, researchers believe this is largely due to urbanization: Cities tend to have better health and sanitation infrastructure, and simply host fewer natural organisms, he explained.
Skylar Hopkins, an associate professor at North Carolina State University who was not involved in the research, cautioned against applying the findings too broadly. Analyzes like this are made up of a selection of complete studies, but they cannot represent a truly random sample of pathogens and infections, he said.
Not all parasites are “bad,” he added, and it cannot be taken for granted that repairing lost biodiversity will undo the rise in disease.
The research published Wednesday builds on previous findings linking the spread of diseases to specific global changes.
For example, extreme heat and rainfall related to human-caused climate change are known to have allowed malaria cases to increase, and could cause them to skyrocket even further in the coming decades. Biodiversity losses are known to contribute to the spread of diseases such as Covid-19, HIV/AIDS, Ebola and severe acute respiratory syndrome (SARS).
However, the researchers point out that there is still much to know about how multiple human influences on the environment can accumulate on each other.
“For example, climate change and chemical pollution can lead to habitat loss and change, which in turn can cause biodiversity loss and facilitate the introduction of species,” the researchers write. New studies will have to examine whether these factors, in combination, serve to add, subtract or even multiply the risks of disease spread.
Taken from Infobae
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