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Spilling over

How the COVID-19 pandemic is just the tip of the iceberg
Connect Research Spilling over

We might still be battling the current COVID-19 pandemic, but unless we change course on the processes that drive disease outbreaks, we could be headed for a ‘pandemic era’. Like something from the pages of a science fiction novel, two years ago the World Health Organization (WHO) called for research into ‘Disease X’. The mysteriously named disease represented the knowledge that a serious international epidemic could be caused by an unknown pathogen.

Two years later and ‘Disease X’ seems to have been unmasked, revealing itself to be the coronavirus the world has become familiar with, COVID-19. However, this story is far from over. WHO still lists ‘Disease X’ as apriority disease alongside COVID-19, Zika, Nipah, Ebola and several other known viruses.

Words: Tom Hills
Illustration: Abigail Burch

The big picture: pandemics are on the rise. And the next pandemic is most likely to be caused by a virus jumping from an animal to a human. If that sounds familiar, it is. HIV, Ebola, COVID-19 and many other viruses have been linked to animals. Like many people, through the course of the pandemic I have become an armchair virologist. Armed with my rudimentary knowledge, I wanted to seek answers to some pertinent questions – how and why do viruses ‘jump’ from animals to humans? What can we do to prevent it and another pandemic?

Steve Dunham, Associate Professor of Veterinary Virology at the University of Nottingham is a qualified vet and is part of the One Virology group at the University, bringing together an interdisciplinary team of researchers with expertise in human and veterinary viruses to make new discoveries, deepen scientific understanding and pioneer novel approaches to challenging infections. I spoke to Steve to explore these questions and understand the mechanics of a pandemic.

Tom Hills: Let's start with the basics. What exactly is a virus and how does it cause disease?

Steve Dunham: A virus is something that is smaller than bacteria and smaller than our cells in our body. Typically, they consist of some RNA or DNA with an outer protein coat. They’re strange things because they can’t replicate themselves without the help of a cell within an animal, human or other organism.

Viruses can cause diseases in many different ways. Typically, viruses infect only limited types of cell. They can do that because the proteins on the outside of the virus recognise proteins on the surface of the cells. The virus will stick to the cell surface, then enter the cell and then proceed to replicate.

Every disease is different in terms of the cells a virus will target. For example, Ebola will cause lesions in your blood vessels, causing a lot of bleeding because the virus is targeting cells that line the blood vessels. That’s an example of acute disease, but viruses also cause disease over a longer period. Some viruses can hide within the body, HIV would be a prime example of that.

TH: Ebola and HIV have both been linked to animals, as has COVID-19, so how do these viruses move between animals and humans?

SD: We refer to animals in which viruses live and replicate as reservoirs of infection. When viruses move from one species to another we call this a spillover event, for example, HIV moving from primates to humans.

There’s also a couple of examples where viruses have gone into pigs initially and then spilled over into humans. One outbreak happened in Australia with Menangle virus – a pig farm was built next to a river and trees which were home to roosting bats. It turned out the bats were flying out into the piggery at night, sitting above the pigs’ food and urinating onto the food. The pigs were then infected with the virus leading to a large number of stillborn piglets. The virus transmitted to humans who were in close contact with the pigs, but it only caused fairly mild symptoms.

A similar situation occurred with Nipah virus in Indonesia. However, Nipah causes a nasty range of illnesses from asymptomatic infection to respiratory illness and fatal encephalitis. Of course, insects may also have a role in transmission. Once you have a reservoir in animals, there’s nothing to stop biting insects such as mosquitoes acting as a go between the animal and humans as well.

TH: We're seeing an increase in the number of outbreaks in recent years, why is that?

SD: Spillover events are always somewhat random and there are lots of factors involved – however, the more humans interact with wildlife reservoirs, the more likely it is to happen.

The reasons these interactions are increasing are complex. For example, animals in the rainforest in Brazil might have been in that environment for thousands of years but as we cut down the rainforest to make space for farming, the likelihood of humans interacting with those animals increases. Likewise, as populations increase in western Africa, the need to eat bushmeat might increase.

TH: What can we do to prevent future outbreaks?

SD: Top of the list is changing the way we interact with wildlife. Whether that’s creating protected habitats for wildlife to prevent human encroachment or stopping the exploitation of wildlife for alternative medicines or for bushmeat. Minimising interaction is also about minimising practices like deforestation. When we take away a habitat like the rainforest, the animals that live there need to find new homes – which can bring human populations and animal reservoirs closer together.

We also need to look at biosecurity measures in farming. You wouldn’t believe the number of times you’ll see a pond built next to a chicken farm, for example. While it might seem like a nice thing to do, ducks encroach into the environment and can pass avian influenza onto the chickens. Then there is potential for an outbreak in humans. Another important consideration is how we develop sustainable farming and food production systems so people all over the world have enough food to eat and are not driven to depend on wildlife as a food source.

Once there’s an initial transmission event of any virus we need to think about the immediate next steps. We have to be very open about it and initiate a local lockdown. It’s been reported that the COVID-19 outbreak was covered up very early on, but obviously that’s not helpful at all.

TH: Is there a positive outlook for the future?

SD: We have a lot of very clever people throughout the world working on different aspects of COVID-19. Here at Nottingham there’s lots of research going on – virologists at our Wolfson Centre for Global Virus Research are working on a DNA vaccine for COVID-19 with Nottingham Trent University. We also have a study underway to look at how we detect early cases of COVID-19.

There are better tools available to us now than there were – we can get the whole sequence of an emerging virus almost overnight whereas years ago it would have taken us best part of a year to do that. There’s funding available with such huge interest in developing vaccines too. However, the immune system is extremely complicated and differs between individuals and ethnic groups, so work in this area does take time.

I think there’s greater awareness of how the way we interact with the environment can affect the likelihood of disease outbreaks. However, change in this area isn’t something we can do individually, it takes global change and governments to make that happen.