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Seven ways a new pandemic could arise and ways to reduce the risk identified by University of Cambridge-led team

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Seven routes by which pandemics could occur - and 161 ways of reducing the risk – have been identified by an international team of wildlife and veterinary experts.

Headed by Prof William Sutherland, at the University of Cambridge, the team calls for widespread changes to the way we interact with animals.

A vet at a pig farm
A vet at a pig farm

Policies that address one issue, such as the trade in wild animals, will not be sufficient, they warn.

While there is ongoing discussion over the source of the Covid-19 pandemic, it is thought to have originated in a wild animal –probably a bat, which infected another animal, potentially a pangolin, in which it mutated into something that could infect humans. A wet market where wild animals were sold in Wuhan, China, was at the epicentre of the outbreak of the novel coronavirus.

Diseases that transfer from animals to humans are known as zoonotic.

The report notes: “Several other major recent epidemic disease outbreaks have zoonotic origins including HIV-AIDS, Ebola and SARS; 60 per cent of human emerging disease events are caused by zoonotic pathogens, with most (72 per cent) originating in wildlife.

“Furthermore, of the known human pathogens, most are zoonotic (80 per cent of viruses, 50 per cent of bacteria, 40 per cent of fungi, 70 per cent of protozoa and 95 per cent of helminths).

“Although most zoonotic pathogens are not capable of sustained human to human transmission, some can cause major epidemic episodes; thus, preventing the transfer of pathogens from other animal species into humans is a major societal challenge.”

But the authors suggest well-meaning but simplistic actions such as complete bans on hunting and wildlife trade, ‘wet markets’ or the consumption of wild animals may be unachievable and would not prevent another pandemic.

They point out that such measures would be difficult to implement. Careful planning would be needed to prevent the proliferation of illegal trade, or alienation and increasing hardship for those local communities across the world who depend on wild animals as food.

Bats have extraordinary DNA damage repair mechanisms that enable them to survive many viruses
Bats have extraordinary DNA damage repair mechanisms that enable them to survive many viruses

The report notes that zoonotic diseases of epidemic potential can be transmitted from farmed wildlife, such as civets. It was civets sold for meat in local markets of China’s Yunnan province that enabled the SARS virus to be transmitted from horseshoe bats to humans, killing 774 people in 2002-3.

Meanwhile, swine flu and avian flu indicates how domesticated animals can be the source of such pandemics.

The study reports: “The rate of zoonotic pathogen emergence is increasing globally and human population density is a strong predictor of emerging disease events, indicating that pathogen emergence is driven by human-induced change bringing wildlife, livestock and humans into closer and more frequent contact.”

Our global connectivity magnifies the likelihood of the “spillover and spread” of pathogens, the authors add.

And they note: “Pathogen transmission from wildlife to humans is influenced by extrinsic factors, such as land-use change and agricultural intensification.

“Such factors play a particularly important role in driving the emergence of zoonotic diseases in biodiverse tropical forest regions, where expanding human populations (and associated agriculture or other activities) into natural habitats leads to increased opportunities for human to wildlife contact and increased pathogen transmission at human–livestock–wildlife interfaces.”

The international team of 25 experts identify some of the major ways another human pandemic could arise, including:

  • wildlife farming
  • wildlife transport, trade and consumption;
  • international or long distance trade of livestock;
  • international trade of exotic animals for pets;
  • increased human encroachment into wildlife habitats;
  • antimicrobial resistance – especially in relation to intensive farming and pollution; and
  • bioterrorism.

While there are some simple ways to reduce the risk of another pandemic – such as encouraging smallholder farmers to keep chickens or ducks away from people – there are others that require significant financial investment on a global scale, such as improving biosecurity and introducing adequate veterinary and hygiene standards for farmed animals across the world.

A market in Shanghai, China, that sells live birds such as chicken, geese and smaller birds
A market in Shanghai, China, that sells live birds such as chicken, geese and smaller birds

Prof Sutherland, of the Department of Zoology and the BioRISC Research Initiative at St Catharine’s College, said: “A lot of recent campaigns have focused on banning the trade of wild animals, and dealing with wild animal trade is really important, yet it’s only one of many potential routes of infection.

“We should not assume the next pandemic will arise in the same way as Covid-19; we need to be acting on a wider scale to reduce the risk.”

They use an approach called solution scanning, which mines ideas from a wide variety of sources such as scientific literature and experts in a range of fields, to identify 161 options for reducing future pandemic risk. They include:

  • Introducing laws to prevent the mixing of different wild animals or the mixing of wild and domestic animals during transport and at markets;
  • Switching more of our diet to plant-based foods to reduce consumption of, and demand for, animal products;
  • Ensuring there are safety protocols for caving in areas with high bat density, such as the use of waterproof coveralls and masks;
  • Improving animal health on farms by limiting stocking densities and ensuring high standards of veterinary care;
  • Identifying and protecting areas with high biodiversity or important habitat features that are at risk from land-use change, particularly those with high-risk species, such as bats;
  • Increasing the efficiency of patrols to detect and prevent hunting, collection or disturbance of high-risk wildlife species; and
  • Identifying high-risk species for zoonotic emergence and disincentivising their hunting/collecting and possession, live or as body parts and products.

Dr Silviu Petrovan, a veterinarian and wildlife expert from the University of Cambridge and lead author of the study, said: “We can’t completely prevent further pandemics, but there are a range of options that can substantially reduce the risk.

“Most zoonotic pathogens are not capable of sustained human-to-human transmission, but some can cause major epidemics. Preventing their transfer to humans is a major challenge for society and also a priority for protecting public health.”

There are many mechanisms of transmission, the report makes clear, given the abundance of ways humans interact with animals, meaning there are also multiple means of reducing the risk.

It says: “Transmission routes may rely upon direct contact between wild animals and domestic herds or flocks, for example in periodic avian influenza outbreaks. Thus, designing suitable enclosures that preclude the entry of wild animals as well as preventing domestic animals from accessing wildlife habitat can reduce the risk of such events.

“This is particularly relevant for intensive livestock production in biodiverse areas, where biosecurity standards are sometimes not as strict as elsewhere. Examples include Nipah emergence in Malaysia in 1999, swine flu and avian flu epidemics and swine acute diarrhoea syndrome coronavirus (SADS-CoV) emergence in China in 2016 due to a coronavirus spilling over from bats into an intensive pig farm, then spreading amongst farms.”

Intensive pig farming. A vet wearing a protective suit
Intensive pig farming. A vet wearing a protective suit

And it warns: “Contamination of human water sources and food pre or during harvesting also presents a risk, particularly for produce consumed fresh, and raw produce that undergoes little processing, with examples including emerging infectious disease epidemics such as the Nipah virus outbreaks linked to bats contaminating date palm-sap collection vessels.”

The team examined measures that could be taken at local, regional and international scales and did not consider the development of vaccines, medical or veterinary medicine options.

Professor Andrew Cunningham, deputy director of science at the Zoological Society of London and co-author of the study, noted: “Wild animals aren’t the problem – they don’t cause disease emergence. People do. At the root of the problem is human behaviour, so changing this provides the solution.”

They considered all types of animals – wildlife, captive, feral, and domestic – for the study and focused on diseases, particularly viruses, that could rapidly become epidemics through high rates of human-to-human transmission once they have jumped from an animal.

This meant they excluded some zoonotic diseases such as rabies and Lyme disease, which require continuous transmission from animals.

The options they present are not recommendations, but options to be considered by policy makers.

Among the other Cambridge authors were David Aldridge, Harriet Bartlett, Andrew Bladon, Steven Broad, Donald Broom, Neil Burgess, Thomas White and James Wood.

The report, funded by The David and Claudia Harding Foundation, Arcadia, and MAVA. is currently being peer reviewed, but a pre-print can be read at https://osf.io/4t3en/.

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