In a world hyper-attuned to disease after more than two years of a global pandemic, every new outbreak attracts headlines.
The globe is still grappling with COVID-19, but Australians have had to get their heads around the symptoms and risks associated with a number of other new diseases.
Take Japanese encephalitis virus (JEV), which was found in the country’s south-east for the first time early this year.
The mosquito-borne virus is still rare, and cause for caution rather than alarm.
But it’s just one example of the kinds of health challenges scientists say we should expect to see more of as the globe continues to warm.
“Of course, they’re not all at the same level as COVID-19. But the frequency of the events of pandemics are certainly on the increase,” Paul De Barro, senior principal research scientist at the CSIRO says.
Mosquito-borne illnesses do better as the world warms
The science is clear: human activity has warmed the world by about 1 degree Celsius since pre-industrial times. With that comes more extreme and unexpected weather events.
One big challenge facing the globe is what’s known as vector-borne diseases. With malaria, dengue fever and JEV, the vector is the mosquito.
“Put simply, vectors … do better in a warmer world,” a 2020 report in the journal Nature Immunology found.
JEV has been present in parts of far northern Australia like the Tiwi Islands and the top of Cape York for years, but had never been detected further south until this year.
Most people do not experience symptoms, but about 1 per cent have fever and headache — and in rare, severe cases, it can cause serious brain swelling. It’s been linked to at least five deaths in Australia.
“Increasing rainfall leading to flooding can create the preconditions for the main vector of Japanese encephalitis,” Dr De Barro says.
“And that has two additional components — increased rainfall and water birds, which are intermediary hosts for the virus, and also feral pigs do much better.
“So you’ve got greater sources of the virus and lots more of the mosquitoes that are able to spread it.”
It’s the kind of event scientists have been warning about for at least two decades.
The world’s foremost climate science body, the Intergovernmental Panel on Climate Change (IPCC), has found that the prevalence of vector-borne diseases is already on the rise and could get worse.
There are other factors at play in the way any illness spreads, such as vaccination, insect control, quarantine and even farming practices, and scientists want to make clear climate change is not the only cause.
“If there is a mosquito vector part of that cycle, then the mosquitoes might be alive for an extra week during the year,” University of Queensland associate professor Nicholas Osborne says.
“And that just increases the chance of someone being infected with that mosquito.”
Historically, Australia has successfully managed the risk of deadly mosquito-borne illnesses like malaria and dengue fever which kill hundreds of thousands of people worldwide every year, and are prevalent in neighbouring countries.
But those may become more difficult as the climate changes.
Viruses spread by animals are on the rise
Another new virus which has landed in Australia this year is monkeypox, which causes causes flu-like symptoms and a distinctive skin rash after human-to-human contact.
Once again, it’s important to note that the outbreak of the virus is not a cause for panic.
And climate change is one factor — the increasing number of outbreaks could partially be the result of declining levels of immunity to poxviruses in the general population.
All evidence suggests COVID-19 has zoonotic origins.
There are a staggering 10,000 viruses currently circulating in wild mammals which have the capacity to infect humans, a peer-reviewed study published by the journal Nature in April found.
The potential for cross-species transmission is rising as the climate changes and humans move into areas where they interact more with animals that were once geographically isolated, according to the study.
“What we’re seeing is increased frequency,” Dr De Barro says.
“So we’ve seen, say, in the last 20 years, far more outbreaks associated with zoonotic diseases than we saw, say, in the previous 20 years.”
That includes the swine flu pandemic, caused by the H1N1 virus, and the concerning bird flu outbreaks, caused by the H5N1 virus.
One of the key findings of the April study from Nature was that climate change could easily become a dominant force in cross-species transmission of viruses “which will undoubtedly have a downstream impact on human health and pandemic risk”.
In a world that has already passed 1C degrees of global warming, the authors cautioned that much of that cross-species viral sharing may already have happened.
The World Health Organization’s Mike Ryan warned at the start of the month that rapidly changing weather conditions like drought, exacerbated by climate change, were causing animals and humans to change their behaviour.
Dr Ryan pointed to the recent monkeypox outbreaks, an upward trend in cases of Lassa fever, spread by the common African rat, and the increased frequency of Ebola outbreaks.
“So, I think this is a lesson, these diseases will continue to emerge, they will continue to pressure, they will continue to cross the species barrier,” he said.
“The question is: are we in a position to collectively respond?”
There are opportunities to adapt
Of course, as the globe warms, we need to be ready for health impacts more directly caused by that heat.
“Heat is going to affect our health in many different ways,” the University of Queensland’s Dr Osborne says.
“And I suppose this is where a changing climate is seen as so important and why we’re striving to do something about it.”
The IPCC expects climate change to cause about 250,000 additional deaths per year, from malnutrition, malaria, diarrhoea and heat stress, between 2030 and 2050.
Australia may initially escape the brunt of these challenges, with countries with more widespread poverty more likely to be first affected, but will not be entirely spared.
But there are some glimmers of optimism among all the doom and gloom.
Scientists are working hard to find ways to reduce the risk of health outcomes from environmental change, including the newly created Australian HEAL network, of which Dr Osborne is a member.
The IPCC’s April report found the globe already had the tools available to keep global warming under 1.5C. But it warned there must be “transformational change” immediately if that was to occur.
“I am encouraged by climate action being taken in many countries. There are policies, regulations and market instruments that are proving effective. If these are scaled up and applied more widely and equitably, they can support deep emissions reductions and stimulate innovation,” IPCC chair Hoesung Lee said in April.