Understanding the disease spillover from wild to domestic animals

Professor Michael Ward is Chair of Veterinary Public Health and Food Safety at the University of Sydney aims to generate a new understanding of the interface between wild and domestic animals to allow advanced assessment of the risk of microbial spillover.

During a five-year veterinary science degree, you do placements. When I was a student, I soon realised that working in a private practice, day in and day out, mainly seeing just dogs and cats, might be a bit monotonous.

I discovered there’s so much more you can do. I was really interested in infectious diseases and epidemiology – I love that stuff. These are global issues, and you have to get out into the field collecting samples and making observations. Then it comes down to a desktop-based understanding of the data you’ve collected. As an epidemiologist, it’s all about those numbers. It was a perfect fit for me.

My work focuses on the interface between wild and domestic animals and disease spillover risk. People often point at a problem, like Covid, and say, “Oh, that happened due to the wild-domestic animal interface”, without trying to understand what that actually is.

That’s where my research comes in. What creates that interface? What drives it? Is it always there? Does it change? Is it dependent on different species, different landscapes? What are the pieces that come together to form this disease spillover risk? And if it is a risk, what might happen? Could it end up affecting global human populations or global animal populations?

That’s the kind of thinking behind my research, with a view to keeping Australia as disease-free as possible, and developing an understanding about the diseases that will inevitably come here, so hopefully we can be ready for them.

The Covid Wuhan market scenario is, from what I’ve read, a very boring, very straightforward type of interface. I mean, what do you expect when people bring caged wild animals and put them right on top of cages holding chickens or ducks? It wouldn’t take much to write that one up. The conclusion? Don’t do it.

Case studies focus on animals

I supported my application for an ARC Laureate with four different case studies based on more complex work I’ve already been doing.

Bird flu highlights the problem exactly. It has appeared before in Northern Europe and the US, but until very recently rarely in Australia. The obvious question: why is it happening now? And it’s a great question.

Is it a new interface between wild and domestic animals that has been created? Is contact between wild birds and domestic birds much more likely now? Is it because of free-range chicken and egg production? Is it that the wild birds are moving because their food sources have changed, or their breeding cycle has changed, or is it climate change?

There are no obvious answers. People come up with all these pieces of information, and it’s like a massive jigsaw puzzle putting them together.

Another area I’ve been working on is a disease called leptospirosis. It used to be called Canecutters’ disease because agricultural workers in Far North Queensland would get it in the cane fields from rats, and it was seen a lot in Queensland. People milking cows will get it, as it’s present in the cows’ urine. If that gets in your conjunctiva, or if you’ve got cuts, you could get infected.

There tend to be outbreaks every time there’s flooding, or in those parts of the world where there’s poor drainage and contaminated water. We hadn’t really seen it much in Sydney until 2017 when we started seeing lots of cases in dogs in the centre of Sydney – in suburbs like Surry Hills and Redfern.

This was really curious. Why did it suddenly start appearing after seemingly being absent for decades? Then came all the theories. One was that the earthworks from the light rail construction was displacing rats – which seemed a bit far-fetched. There were quite a few flooding events that might have been linked to it, through other species, and we’ve done work on that. We’ve looked at parks in Sydney, and found it’s actually in the environment everywhere – under playground equipment, in the water drinking bowls left out for dogs. It’s also in the rats, but is it in the bats? Is it in the possums? That’s another case study. What’s going on? What’s caused this change?

My third case study is looking at the rabies spreading in Indonesia. Famously, there was an outbreak in animals in Bali in 2008, and it’s now getting very close to PNG and Northern Australia.

We’re looking at doing some modelling to try to predict what might happen if it arrived on our mainland. We did a lot of work with domestic dogs in Indigenous communities up in Cape York and the Torres Strait, and how the disease might spread in the wild dog population, among the dingoes – trying to work out the contact patterns between wild dogs and domestic dogs.

Domestic dogs up there are allowed to roam. It’s a very different sort of culture compared to urban areas. We also see dingoes coming very close to the townships. Again, you’ve got that wild versus domestic interface.

My fourth case study has been up in the Kimberley in WA looking at feral pigs and domestic cattle. Around Fitzroy Crossing you’ve got a large feral pig population mingling with cattle. We took samples from feral pigs to see if there’s been any contact, based on the microbes they harbour.

Again, it’s the same theme. What are the main drivers of these interactions between animals? Hopefully in the future we can create an international collaborative centre, either through the UN Food and Agriculture Organisation, or the World Organisation for Animal Health, to put all this information into a risk assessment framework. That way, people can plug in their own information and understand the risks associated with a situation, wherever it might be. We could include a qualitative scale to show whether it’s high risk or low risk. We will make these tools available to the international community, so people all over the world can make better informed decisions.

As told to Graem Sims

Also in this series 2024 ARC Laureate Fellows:

Energy transition and communities: Professor Chris Gibson

Plate tectonics: Professor Alan Collins

Predicting groundwater discharge Professor Andrew Baker

Unravelling the mysteries of the immune system Professor Gabrielle Belz

Researchers hope to monitor Antarctic vegetation remotely Professor Sharon Robinson

How to build a quantum computer Professor Andrea Morello