Animals that carry disease-causing micro-organisms, or pathogens, that make people ill thrive well in human habitats, scientists have found.
In a study led by University College London, experts found that human-managed ecosystems harbour more species that are potential hosts of infectious diseases when compared to undisturbed natural habitats.
The researchers say that global changes in land use, such as the conversion of natural habitats to agricultural land or cities, is benefiting animals carrying diseases known to infect people.
As the world continues to come to grips with the COVID-19 pandemic, the scientists warn that humans may need to alter how land is used to reduce the risk of future spillovers of pathogens that originate in animals.
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Rory Gibb, a PhD candidate at UCL’s Centre for Biodiversity & Environment Research, and lead author on the study, published in the journal Nature, said: “The way humans change landscapes across the world, from natural forest to farmland for example, has consistent impacts on many wild animal species, causing some to decline while some others persist or increase.
“Our findings show that the animals that remain in more human-dominated environments are those that are more likely to carry infectious diseases that can make people sick.”
Zoonoses are diseases caused by pathogens that are naturally carried by animals, and that regularly or occasionally transmit (‘spillover’) to people – think plague, SARS-CoVs, Ebola, leishmaniasis, Lyme disease… 3/ pic.twitter.com/ARiTpSlpC1
— Rory Gibb (@roryjgibb) August 5, 2020
It is widely accepted that changes in land use increases the risk of emergence of diseases which can jump from animals to people, known as zoonotic diseases.
But whether the conversion of natural habitats to human use favours species that host zoonotic pathogens has remained unclear.
So a team of researchers looked at evidence gathered from 6,801 ecological communities, spanning across six continents.
The data was collected from 184 studies involving nearly 7,000 species, 376 of which are known to share pathogens with humans.
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They found that animals known to carry pathogens were more common in human-dominated landscapes, when compared to more wild habitats.
The researchers found that the number of animals who did not carry zoonotic pathogens declined while species with disease-causing micro-organisms increased with human land use.
This effect was found to be strongest for rodents, bats and passerine bird species.
Senior author Professor Kate Jones, of UCL’s Centre for Biodiversity & Environment Research and ZSL Institute of Zoology, said: “Global land use change is primarily characterised by the conversion of natural landscapes for agriculture, particularly for food production.
“Our findings underscore the need to manage agricultural landscapes to protect the health of local people while also ensuring their food security.”
She added: “As agricultural and urban lands are predicted to continue expanding in the coming decades, we should be strengthening disease surveillance and healthcare provision in those areas that are undergoing a lot of land disturbance, as they are increasingly likely to have animals that could be hosting harmful pathogens.”
Reader Q&A: Can humans pass viruses to animals?
Asked by: Richard O’Neill, Glasgow
Animals are a notorious source of infections in humans. The Spanish Flu Pandemic, which killed over 20 million people between 1918 and 1920, is believed by many researchers to have had its origins in a virus carried by birds. But humans are also capable of passing on deadly viruses and bacteria to animals, in a phenomenon known as reverse zoonosis.
Some serious human diseases cause relatively mild health problems in other animals. For example, diphtheria – which is potentially fatal in humans – causes nothing more than ulcers on cattle. But other human infections, such as hepatitis and influenza, remain just as deadly if transmitted to animals via contact with humans in farms, zoos or veterinary surgeries. There have even been cases of tuberculosis claiming the lives of circus elephants following infection from humans.