A TIGER pads into a reserve village in the Pilibhit region on the Indian Nepalese border searching for food. Villagers panic and hide inside their homes; several people have been killed in the past year. Eventually the tiger is tranquilised and returned to nearby forest.
Tigers are normally wary of humans – they walk into villages only because they have nowhere else to go. In the previous twenty-five years forest cover in the region has been reduced by two thirds to just 22 percent.
Cutting down forests isn’t just a problem for tigers or villagers – it is also one of the reasons pandemics are becoming increasingly common, because deforestation results in increased contact between wild animals and humans.
Treat or prevent pandemics?
In May this year another deadly Ebola outbreak was discovered in the Congo, causing widespread panic and fear. It is thought that the virus spread from fruit bats to monkeys and then humans who ate bush meat. It is the ninth outbreak since Ebola was discovered in the 1970s. The last outbreak in 2014 in West Africa claimed more than 11,000 lives while the cost of controlling the disease, along with the impact on the economy, was in the order of billions of dollars.
Every year an estimated 14 million people die from infectious diseases. Three quarters of these diseases came from animals and the majority of these are wild animals. Billions are spent controlling these diseases, and the economic impact can be devastating even after an outbreak has been controlled. With the Malaysian Nipah virus outbreak in 1998-1999 there were around 100 human casualties, but more than one million pigs were euthanized. The Zika outbreak during the 2016 Rio Olympics cost Latin American countries billions, much of it due to lost tourism revenue.
The priority response to these epidemics has been to treat or limit diseases via vaccines, drugs or quarantine. But responding after an outbreak can be slow, especially if there is a need to create drugs or vaccines. Creating new vaccines is time consuming and extremely expensive. Even if there is a vaccine, it’s not always possible to vaccinate everyone.
What if pandemics could be prevented instead or treated?
Mapping disease hot spots
The origin of pandemics is not random, according to Dr Moreno Di Marco, a conservation biologist at CSIRO. Di Marco uses ecological modeling to predict the impact of global change on biodiversity, and the consequences this has for humanity.
To better understand where pandemics come from, Di Marco contributed to research led by EcoHealth Alliance in the US, where they created a database of global disease hotspots and analysed the relationship between environmental, demographic and biological factors, which they discuss in a 2017 Nature Communications paper.
“We found that the risk of disease emergence is due to increasing interaction between humans, domestic and wild animals,” says Di Marco.
The increased interaction is due to habitat destruction caused by increasing human population needing to convert more land for producing food and energy.
“Areas of high biodiversity are more likely to host pathogens that could be transferred to humans, hence the risk of disease emergence from habitat modification is particularly high,” says Di Marco.
This is because disease risk is related to diversity of mammals. As humans are also mammals, it is relatively easy for viruses or pathogens to be transferred to people.
“Bats and rodents are the main groups associated with infection to humans,” says Di Marco.
The areas of highest mammal diversity are located in the tropics. This means most of the world’s global hotspots for infectious diseases emergence are located in developing countries.
Another link in the puzzle is increased human population densities and mobility – the more people move around, the more likely it is that disease will spread.
Is Australia at risk?
Australia has one of the highest diversity of species on the planet and large parts of Australia are in the tropics. Australia is also home to a large population of fruit bats, all in the Pteropodidae family – the same family that was probably responsible for Ebola. Increasingly, fruit bats are taking up residences in cities as forests are being cut down for agriculture. This puts them in closer proximity to people.
Already Australia has faced a Hendra outbreak, which was due to fruit bats transferring the Hendra virus to horses. When horses stand under a tree which hosts a population of fruit bats they are at risk of receiving the virus often via urine or faeces.
“Australia hosts bat populations which fly to PNG from north Queensland – so there is a risk of pathogen transmission between countries,” says Di Marco.
Di Marco also stresses that Australia is part of an increasingly connected world, which increases the risk of human-to-human transmission.
Disease surveillance is expensive so it’s important to control key risk factors. According to Di Marco the key risk factor is habitat modification.
He also says changed densities of livestock and change in the composition of wildlife will affect the likelihood of a disease outbreak.
Di Marco stresses that predicting the location of the next infectious disease outbreak and responding to these predictions is a complex interdisciplinary problem.
To improve global understanding of how to predict pandemics, Di Marco coordinated a CSIRO Cutting Edge Symposium in May on ecological modeling for disease prediction. The Symposium was organized in collaboration with Simon Ferrier, Mario Herrero and Michelle Baker, and included researchers from the EcoHealth Alliance in the US. It’s the kind of international, cross-disciplinary collaboration required to broaden understanding of this complex problem to improve outcomes in the future.
Published in Ecos, May 2018.