Zoonotic disease and the use – and abuse – of animals.

We live in a highly interconnected ‘global village’; linked closely to one another and all other life on Earth. Diseases emerge, spread, and persist in human populations, wildlife, and farmed animals, affecting all three with often devastating consequences.

Devastating diseases that make this ‘jump’ between animals and humans are called zoonotic diseases — and they’re on the rise. Global human health has, therefore, become increasingly intertwined with the health of our environment and the animals we share it with.^[1]

Pathogens can spread between animals and humans when we are in close contact, and there is an increased risk from exposure to infected bodily fluids (for example blood, birthing liquids, respiratory droplets, mucous, urine and faeces). Such exposure primarily occurs on farms, during hunting and slaughtering, or at animal sale yards and live animal markets.

This puts the people who work as farmers, hunters, slaughterers, and veterinarians, as well as those who live close to them or near places where these activities occur, at a higher risk of contracting and spreading zoonotic diseases.

The consumption of farmed animals and wildlife has fuelled numerous pandemics and epidemics across the globe. Increasing demand for animal-based foods and other products has led to the intensive farming of domesticated and wild animal species, as well as an increase in ‘bushmeat’ hunting and the trade in wildlife — all of which have profoundly increased the emergence of zoonotic diseases.

The risk of disease outbreaks is greatly increased by the conditions inside factory farms which include high levels of pollutants, close contact with sick and dead animals, and suppressed immune responses from stress — which have contributed to the emergence of bird flu, swine flu and Middle East Respiratory Syndrome (MERS). The intensification of animal farming has further been linked to the evolution of anthrax, measles, and whooping cough (pertussis).^[2][3]

Additionally, direct or indirect contact with wild animals is inevitable, as native habitats are destroyed and farms encroach further on forests, jungles, and other natural environments. This provides an opportunity for novel pathogens to become established in farmed animals and, subsequently, humans.

Some of the major infectious diseases emerging from the mixing of farmed or domesticated and wild animals include Severe Acute Respiratory Syndrome (SARS), Nipah Virus and Hendra Virus.^[2] Deforestation and land clearing for animal agriculture are also contributing to climate change. All of these factors have complex impacts on vector-borne illnesses, increasing the abundance or distribution of some mosquitoes and the diseases they cause, including malaria in South America.^[4]

In addition to rearing animals, the slaughtering of animals is a high-risk activity too. For example, the hunting of wild animals caused the emergence of Human Immunodeficiency Virus (HIV) and Ebola Virus Disease^[2]; while the slaughtering of farmed animals frequently exposes people to bacteria causing Q Fever and a variety of other pathogens^[5]; and eating contaminated meat, milk, and eggs is a leading cause of gastrointestinal sickness including Campylobacteriosis and Salmonellosis^[6].

Coronaviruses cause respiratory and gastrointestinal diseases in a range of animals, including humans. Examining past coronavirus outbreaks provides a chilling account of warning signs; starting with human coronavirus OC43, which emerged around 1890 from a bovine (cattle) coronavirus that now causes Shipping Fever disease, potentially resulting in a pandemic event.^[7]

The first new zoonotic disease outbreak of the 21st century was a coronavirus named Severe Acute Respiratory Syndrome (SARS). The disease first emerged in China in 2002 and resulted in 8,098 human cases worldwide with 774 deaths.^[8] SARS jumped to humans from infected Civets; cat-like animals who are intensively farmed for their meat, purported aphrodisiac qualities, and to produce the most expensive coffee in the world.

It is likely the crowded inter-species mixing and immunosuppressive effect of stress enabled the SARS virus to jump from bats to civets and then people in a live animal market.[2] Once identified as the source of SARS, some 10,000 civets in China were culled.^[9] It was later shown that pigs could contract SARS from infected people.^[10]

A decade later, in 2012, another novel zoonotic coronavirus emerged in people in Saudi Arabia, named Middle East Respiratory Syndrome (MERS). An outbreak of the disease occurred from 2014 to 2016 across the Middle East, Asia, North America and Europe, resulting in 2,494 confirmed human cases and 858 deaths.^[11] Though the MERS virus had been circulating among Dromedary camel populations since 1983, it is likely the intensification of camel farming with confined ‘barn’ housing systems contributed to its transmission into humans.^[12]

Just five years later, our world was experiencing the largest, most infectious coronavirus outbreak to date: SARS-CoV-2 causing COVID-19. In late December 2019, a cluster of patients with unusual pneumonia was detected in Wuhan, China — months later, there were millions of confirmed human cases and over one hundred thousand deaths worldwide.^[13] While the origin of COVID-19 was hotly debated, one theory was that it originated in bats and passed through an intermediate host, thought to be the Pangolin, before jumping to humans at a live animal market. Pangolins are the most trafficked mammal in the world; hunted, farmed and sold for their meat and scales used in traditional Chinese medicine.^[14]

Scientists and the US Center for Disease Control and Prevention warn that at least one more coronavirus — Porcine Deltacoronavirus, which has killed tens of thousands of pigs across the US and China — has the potential for further cross-species transmission, posing significant health risks for humans and farmed animals alike.^[15][16]

While some zoonotic diseases are likely inevitable, so much human and animal suffering could have potentially been avoided had we treated animals and the natural world with more care and compassion.

While there is no simple answer to reducing the risk of future pandemics, a global shift towards food systems that are safer and kinder to all could be part of the solution. Choosing plant-based and sustainably grown foods whenever possible is one simple but powerful thing we can do each day as individuals to shape a brighter future — for animals, the environment and ourselves.

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