AUSTRALIA IN THE ASIAN CENTURY – A series examining Australia’s role in the rapidly transforming Asian region. Delivered in partnership with the Australian government.
Here, Professor Martyn Jeggo looks at how we might tackle deadly viruses emerging from Asia.
Unlike most Hollywood disaster movies, last year’s Contagion, based on the scenario of a deadly virus originating in Asia sweeping the world, is not too far from the truth.
The movie’s fictitious virus is based on the Nipah virus, which spreads from bats to pigs to humans. First discovered in Malyasia in 1998, Nipah has killed more than 100 people and led to the culling of more than a million pigs. There were 12 separate outbreaks last year alone.
Nipah is closely related to the Hendra virus, which was first isolated in Queensland in 1994 after it spread from bats, killing 14 horses and a horse trainer. More horses died in cases in Queensland and New South Wales last year and this time the virus was also detected in a dog. Nipah and Hendra have a mortality rate of 40% to 100%.
The threat of currently unknown virus-borne illness spreading across the world in the future is very much in the realm of possibility.
The threat of zoonotic viruses
Viruses are uniquely dangerous because of their ability to mutate and become deadly for existing and new hosts – a characteristic that makes them so much worse than a bacteria, mycoplasma or parasite.
Zoonotic viruses spread from animals to humans and are highly unpredictable. The range of who they can infect (host range) and their speed of transmission makes them a great and real threat.
Three-quarters of emerging viruses in humans have their origins in animals and many originate in South-East Asia. Why should this be? The growing need to feed an increasing population has led to more and more intensive farming practices, leading to close contact between farm workers and masses of animals.
The growing need to feed an increasing population has led to more and more intensive farming practices, leading to close contact between farm workers and masses of animals. Thousands, if not millions, of animals such as pigs and poultry are contained in relatively small areas, enabling viruses to infect large numbers of animals at a single site, and potentially mutate and become more virulent.
The 2003 SARS epidemic is the perfect example of a previously unknown virus causing chaos worldwide as it spread from China to Hong Kong and Canada.
A SARS-like virus was dormant in bats for some time before a chance mutation occurred. This change didn’t take place in a bat but in another host. The civet cat, which was almost certainly infected from bats, is commonly eaten by Chinese people and that’s how SARS was able to infect humans.
Chance virus mutations demonstrate the importance of keeping an open mind when considering what kind of viruses could emerge. We can’t rule out the possibility of wild birds from Asia migrating to the Top End of Australia, for instance, and mingling with native birds to introduce a new influenza virus type that we’ve never seen before.
While some of our most deadly zoonotic viruses originate in bats, they are invariably merely the carrier. Rarely do the viruses cause disease in bats. So our ongoing research into bat-borne viruses is focused on understanding “host switching”.
Similarly, understanding the spillover of influenza viruses from one host to the other, such as bird flu infecting people, will help us better manage risks.
Embracing a one-health approach
Population growth, livestock farming practices, climate change and our impact on the environment have disturbed the ecosystem and increased the risk of viruses spreading. There are also more of us travelling around the world, and that can only encourage the spread of viruses.
Only by considering the whole ecosystem in which bats, livestock and humans co-exist can we better understand what leads to the spread of viruses, and how best to curb their impact.
Looking at health controls for people working on intensive livestock farms in Asia might be one way to address this potential risk. But the growing popularity of more eco-farming practices, such as free-range chickens, could also be putting livestock at more risk. As they roam freely across open areas, animals potentially come in contact with wild birds carrying exotic viruses.
Traditionally, we’ve approached wildlife, animal and human diseases entirely separately. The way forward may be to take a “one-health” approach with scientists across all three disciplines working together to understand the system as a whole. To deal with zoonotic viruses, we need to understand the multidimensional links between wild animals, livestock production, the environment and global public health.
Understanding the mechanism of host switching and putting this in the context of our ecosystem is perhaps the best approach to predicting and preempting future virus risks.
This “one-health” approach has already been successful in the development of a vaccine against the Hendra virus. By working together, we realised that there really isn’t anything we could do about the bats. And that vaccinating people costs too much and takes too long. But from our bat-based research, we were able to create a vaccine for horses against Hendra expected to be available next year.
The introduction of the vaccine will mean horses are protected and can’t spread the disease so humans. People won’t be put at risk and the bats hosted the virus all along will no longer be considered such a threat.
Out ongoing research into viruses will take the guesswork out of the contagions that lie ahead. And that calls for a collective sigh of relief.
This is part twelve of Australia in the Asian Century. You can read other instalments by clicking the links below:
Part Fifteen: How Australia can become Asia’s food bowl