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The virus that causes COVID-19 wasn’t the first pathogen to pass from animals to humans, and it sure won’t be the last. And while we can never identify the exact animal source of SARS-CoV-2, we can refine our (re) research strategies to prepare for the next one.
To do this, a new study quantified the risk of naturally circulating viruses passing from their animal hosts, especially mammals, to humans – with a focus on the global wildlife trade, both legal. and illegal.
A quarter of mammals taken into the wildlife trade harbor 75 percent of all known zoonotic viruses, but domesticated and non-traded wild mammals were not far either, according to the research.
“Each year, it is estimated that the international wildlife trade results in more than a billion direct and indirect contacts between wildlife, humans and domestic animals,” says senior author and conservation biologist Shivaprakash Nagaraju of The Nature Conservancy, India.
Simply put, this close contact increases the chances of animal pathogens such as viruses spreading in humans, becoming zoonotic diseases that can lead to epidemics.
From the results of this study, it appears that a few key animal groups carry the bulk of zoonotic viruses. The question is: are we looking at the right ones?
“By identifying the species that pose the highest risk of transmitting zoonotic diseases to humans, we hope our research can help global health experts prioritize where to focus their efforts to prevent the next global pandemic,” he said. Nagaraju said.
But it’s not a new risk, it’s just a risk that caught our attention. And the wildlife trade is not the only determining factor.
Six in ten infectious diseases in humans are zoonotic, with plague and rabies listed by the United States Centers for Disease Control and Prevention as zoonoses of concern alongside emerging coronaviruses.
In the past decade alone, Ebola, HIV, Middle East Respiratory Syndrome (MERS), and Severe Acute Respiratory Syndrome (SARS) all emerged as zoonotic viruses before the COVID-19 pandemic hit. installed. So we would be foolish not to recognize our own hand in this.
Growing evidence has shown that exploitative human activities such as deforestation and urbanization that impact natural habitats and bring wildlife into contact with humans, have directly contributed to the spread of disease. zoonotic.
Two main sources of zoonotic diseases are bats and rodents, which live in tightly-knit colonies and easily adapt to human-dominated environments.
But this new study, a meta-analysis of data on 226 known zoonotic viruses in more than 800 mammal species – wild, traded and domesticated – points to other potential sources that may have been overlooked.
In today’s wildlife trade, primates and hoofed animals such as goats, cattle and pigs could pose an even greater risk to human health than bats and rodents – carrying a load. important pathogen, about 30 percent of all known zoonotic viruses.
“Commercialized mammals also harbor a distinct composition of zoonotic viruses and different host reservoirs than non-commercialized and domesticated mammals,” writes Nagaraju.
Outside of the wildlife trade, however, rodents and bats are still the main reservoirs of zoonotic viruses in nature, according to the study.
An analysis like this, however, is only as good as the data available in the literature, reports and databases, and it depends on which viruses were sampled and where.
Despite their valiant efforts, scientists have only scratched the surface of the millions of viruses circulating in wild animals. In mammals and birds alone, there are an estimated 1.7 million undiscovered viruses that we don’t know anything about.
“The phylogenetic viral load signal we detected could be a function of both incomplete sampling of mammalian species for viruses and undiscovered viral diversity in mammals,” Nagaraju and colleagues write in their article. .
That said, other recent studies have also suggested that in surveillance efforts, we need to look beyond bats and rodents, as these animals may not be the “special” viral reservoirs that the research suggests. earlier have revealed. These groups of animals contain more species, which are therefore able to harbor more viruses that can find their way into humans.
This same study also suggested that viral traits, such as how a virus replicates, may be more of a factor in zoonotic fallout than biological characteristics of animal hosts. But other research shows that geography and the distribution of species are also important factors.
Which brings us back to the wildlife trade, a global problem.
A 2009 analysis found that nearly 1.5 billion live animals were imported into the United States between 2000 and 2006, and nearly 80 percent of those shipments contained animals from wild populations. Many were from known zoonotic outbreaks and species identification was generally poor.
“If we want to stop the next pandemic before it starts,” says Joe Kiesecker, also of The Nature Conservancy, “our results indicate that we should, among other measures, focus our efforts on maintaining rodents, bats , primates, ungulates and carnivores not in the wildlife trade. “
“However, managing the wildlife trade is only part of the solution to preventing future zoonotic pandemics,” the researchers also note.
“An equally important threat to zoonotic diseases linked to wildlife is [land-use changes] forests for other uses, such as the expansion of industrialized agriculture, infrastructure development and urbanization.
The study was published in Current biology.
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