Animals that carry infectious diseases like Ebola and the virus causing COVID-19 thrive in human-made habitats such as cities and farmland, scientists have found.
Researchers reviewed 184 studies of 376 host species – animals that pass a virus to humans – including bats, birds, rodents and primates.
They found the conversion of natural habitats to human-used land increases the risk and emergence of ‘zoonotic’ diseases – those that pass from animals to humans.
Changing farming methods may therefore help reduce risk of future infectious disease outbreaks that are as deadly as Covid-19.
Scientists believe the coronavirus that causes Covid-19 likely came from bats, although this has not yet been confirmed.
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Dataset of ecological communities and zoonotic host species. Points on the map show the geographical locations, with mammal survey locations in black and all other sites in red, and countries containing sites shaded in blue. The chart shows the taxonomic distribution of hosts of human-shared pathogens (birds, invertebrates, mammals, reptiles and amphibians
‘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,’ said study Rory Gibb at University College London.
WHAT IS A ZOONOTIC DISEASE?
Zoonotic diseases are able to pass from one species to another.
The infecting agent – called a pathogen – in these diseases is able to cross the species border and still survive.
They range in potency, and are often less dangerous in one species than they are in another.
In order to be successful they rely on long and direct contact with different animals.
Common examples are the strains of influenza that have adapted to survive in humans from various different host animals.
‘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.’
SARS-CoV-2 is the coronavirus responsible for the illness known as Covid-19, which has killed nearly 700,000 people worldwide.
Although the source of the virus is not confirmed, evidence suggests that SARS-CoV-2 has a zoonotic source, meaning it’s spread from animals.
It is widely accepted that changes in land use increases the risk of emergence of zoonotic diseases.
But whether the conversion of natural habitats to human use favours species that host zoonotic pathogens had been unclear.
There was previously no comprehensive analysis of the effects of land use on zoonotic host diversity, the researchers claim.
To learn more, the team considered evidence gathered from 6,801 ecological communities 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, including mammals, birds, invertebrates and reptiles.
Species such as bats that host zoonotic pathogens (which can jump from animals to people) constituted a higher proportion of the animal species found in human-influenced environments compared to the ecological communities in more wild habitats.
The dataset compiles local site-level species data from hundreds of studies where researchers have surveyed ecological communities along gradients of landscape disturbance, from natural vegetation to agricultural and urban ecosystems.
Disease-causing microorganisms that infect humans are more common in landscapes intensively used by people, such as cities and agricultural land, they found.
Animals known to carry pathogens – zoonotic hosts – were more common in human-dominated landscapes, when compared to undisturbed, wilder habitats.
Species that host zoonotic pathogens constituted a higher proportion of the animal species found in human-influenced environments, compared with the ecological communities in more wild habitats.
Mammal species that harbour more pathogens overall – either human-shared or non-human-shared – are also more likely to occur in human-managed ecosystems.
Animals that did not carry zoonotic pathogens declined with human land use, while species with disease-causing micro-organisms increased.
This effect was found to be strongest for rodents, bats and perching birds, known as passerines.
Coronavirus particles under transmission electron microscopy.
Humans may need to alter how land is used to reduce the risk of future spillovers of pathogens that originate in animals.
‘Global land use change is primarily characterised by the conversion of natural landscapes for agriculture, particularly for food production,’ said study author Professor Kate Jones at UCL.
‘Our findings underscore the need to manage agricultural landscapes to protect the health of local people while also ensuring their food security.
‘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.’
The study has been published in Nature.
Since the emergence of SARS-CoV-2 in Wuhan, China late last year there’s been some uncertainty surrounding the virus’s origin.
A previous report from scientists said the virus is 96 per cent identical to one found in bats, although this is yet to be officially confirmed as the source.
SARS-CoV-2 is likely to have its ancestral origins in a bat species but it probably reached humans through an intermediary species.
While it was initially assumed that the virus passed to humans in a Wuhan wet market, more recent studies have pointed to an anteater-like animal called a pangolin being the intermediary animal.
Pangolins are consumed as food in China and are also used in traditional medicine.
Scientists in China believe SARS-CoV-2 came from bats
The human COVID-19 SARS-CoV-2 virus split from its closest known relative – another coronavirus from a horseshoe bat (pictured) – about 30 to 40 years ago, according to University of Sydney Professor Simon Hothe jump to humans most likely happened more recently
Researchers at the Chinese Academy of Sciences, the People’s Liberation Army and Institut Pasteur of Shanghai came to the conclusion that the coronavirus may have come from bats.
In a statement, the team said: ‘The Wuhan coronavirus’ natural host could be bats… but between bats and humans there may be an unknown intermediate.
Research published in the Lancet also determined bats as the most probable original host of the virus after samples were taken from the lungs of nine patients in Wuhan.
The team suggested that bats passed the disease on to an ‘intermediate’ host which was at the Huanan seafood market in Wuhan before being passed on to the ‘terminal host’ — humans.
Authorities have pointed the blame on food markets in Wuhan, the Chinese city at the centre of the outbreak that scientists are scrambling to contain.
Rodents and bats among other animals are slaughtered and sold in traditional ‘wet markets’, which tourists flock to see the ‘real’ side of the country.