Zoonosis and the next pandemic: why hindsight must be 2020

By Calandra Grima, class of 2020.

Image by James Wainscoat, via Unsplash (left); Image by Luke Jones, via Unsplash (right)

From the Black Death, Spanish Influenza and HIV/AIDS, to SARS, Ebola, and now COVID-19. These are just a notable few of the numerous disease outbreaks in human history that originated from animals.

Each of these diseases shook the world when they arose and caused widespread death, illness and fear. Alarmingly, diseases are jumping from animals to humans – known as zoonotic spillover – more often now than they used to.

So, as we look upon empty streets and full ICUs amid a global lockdown and grapple with the devastating toll a pandemic can take on our society, it is vital that we learn from COVID-19 to prevent future zoonotic pandemics from occurring. Our hindsight must rather literally be 2020.

How does zoonotic spillover occur?

Zoonotic spillover occurs when humans and animals are in close contact, allowing a pathogen (e.g. a virus or bacteria) to pass from the animal to a human and cause disease (known as zoonosis). The precise mechanisms involved are still being investigated, however the main causes of zoonotic spillover are being in contact with infected animal bodily fluids or dwellings.

Human history is filled with examples of situations that are perfect storms for zoonotic spillover. The most topical example is the jump of COVID-19 from a bat in a wet market to humans. Another recent example is the 2009 H1N1 swine flu pandemic that arose from a zoonotic spillover between pigs and a young boy that lived nearby a pig farm in Mexico.

Insects such as fleas and mosquitoes can also carry zoonoses – the classic example of this being the flea-ridden rats that carried the Black Death throughout 14th century Europe. Salmonella poisoning from undercooked chicken is an example of food-borne zoonosis, so fellow culinarily-challenged people, please ensure you cook your meals thoroughly.

Why are zoonotic spillovers becoming more frequent?

The United Nations Environment Programme has reported that ‘sixty per cent of known infectious diseases and 75 per cent of emerging infectious diseases are zoonotic’, and worryingly, zoonotic spillovers are occurring at a much higher frequency now than they did 50 years ago.

The big question is why? Why are zoonotic spillovers becoming more common? The answer lies in our land use.

To accommodate an ever-growing human population, the usage of land around the world is changing. More land is being converted from natural habitats into farmland and urban areas, displacing the wildlife that lives there and prompting animals to move into urban and agricultural areas. This, in addition to the trade of wildlife in unhygienic conditions, is resulting in humans and livestock being in contact with wild animals more often, thus allowing zoonotic spillovers to occur more frequently.

Image by Meritt Thomas, via Unsplash (left); Image by Mauricio Livio, via Unsplash (right)

What can we do to prevent zoonotic spillovers occurring?

Zoonoses are a major threat to human health, and scientists have warned policymakers for over a decade that a pandemic such as COVID-19 was inevitable without proper action.

Leading zoonosis expert Dennis Carroll notes that “whatever future threats we’re going to face already exist; they are currently circulating in wildlife. Think of it as viral dark matter. A large pool of viruses are circulating and we don’t become familiar with them until we see a spillover event and people getting ill.”

We can never stop viruses from existing – in fact, there are more viruses on Earth than there are stars in the universe. This means that we must recognise the ones that pose a zoonotic spillover risk and remedy this before we reach another pandemic of COVID-19 proportions.

To prevent future zoonotic pandemics, we must preserve natural habitats to prevent the displacement of wildlife by limiting deforestation and using existing farmland efficiently to prevent the need for expansion. Wildlife trade and livestock farms must be closely monitored to ensure good hygiene and that potentially infected animals are detected before a zoonotic spillover occurs.

These preventative measures can be implemented for a significantly lesser cost than that of a pandemic occurring, and this is only considering the financial cost. If we also include the immeasurable mental, physical and emotional hardship our society has endured throughout this pandemic, it is blatantly obvious that preventative measures are the only way forward.

COVID-19 has taken a catastrophic toll on the world, so we must act in the hindsight of 2020 to avoid the next zoonotic pandemic.

Further reading

Zoonotic Diseases

Global shifts in mammalian population trends reveal key predictors of virus spillover risk