In a world plagued by disease, more than two years after a global pandemic, every new outbreak makes headlines.
The world is still battling COVID-19, but Australians have had to raise their heads about the symptoms and risks associated with many other new diseases.
Take the Japanese encephalitis virus (JEV), which was first detected in the country’s southeast earlier this year.
The mosquito-borne virus is still rare, and is cause for caution rather than alarm.
But this is just one example of the kinds of health challenges scientists say we should expect to see more as the world continues to warm.
“Of course, they are not all at the same level as COVID-19. But the frequency of pandemic events is certainly increasing,” says Paul de Barro, senior principal research scientist at CSIRO.
Mosquito-borne diseases get 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 it come more extreme and unpredictable weather events.
The world is facing a major challenge which is known as vector borne diseases. Along with malaria, dengue fever and JEV, the vector is the mosquito.
“Simply put, vectors … do better in a warmer world,” said a 2020 report in the journal Nature Immunology.
JEV has been present in parts of far northern Australia, such as the Tiwi Islands and the top of Cape York, for years, but was never detected in the south until this year.
Most people do not experience symptoms, but about 1 percent have fever and headache – and in rare, severe cases, it can lead to severe swelling of the brain. It has been linked to at least five deaths in Australia.
“Increased rainfall could lead to flooding, which could make it a prerequisite for the main carriers of Japanese encephalitis,” says Dr. de Baro.
“And it has two additional components – increased rainfall and water birds, which are intermediary hosts for the virus, and wild boars do much better as well.
This is the kind of phenomenon that scientists have been warning about for at least two decades.
The world’s leading climate science body, the Intergovernmental Panel on Climate Change (IPCC), has found that the spread of vector-borne diseases is already on the rise and could get worse.
The way a disease spreads also has other factors, such as vaccination, pest control, quarantine and even farming practices, and scientists want to clarify that climate change is not the only cause.
“If the mosquito is a vector part of that cycle, mosquitoes can live an extra week during the year,” says Associate Professor Nicholas Osborne from the University of Queensland.
“And that increases the chances of someone getting infected with that mosquito.”
Historically, Australia has successfully managed the risk of deadly mosquito-borne diseases such as malaria and dengue fever, which kill hundreds of thousands of people worldwide each year, and are prevalent in neighboring countries.
But they could become more difficult as climate changes.
Animal-transmitted viruses are on the rise
Another new virus that has arrived in Australia this year is monkeypox, which causes flu-like symptoms and a characteristic skin rash after human-to-human contact.
Once again, it is important to note that the virus outbreak is not a cause for panic.
And climate change is a factor – the increasing number of outbreaks may be partly the result of declining levels of immunity to poxviruses in the general population.
The virus is what is known as a zoonotic disease, which is caused by the jumping of germs from animals to humans, then spread from person to person.
All evidence suggests that the origin of COVID-19 is zoonotic.
A peer-reviewed study published by the journal Nature in April found that a staggering 10,000 viruses are currently circulating in wild mammals with the potential to infect humans.
According to the study, the potential for cross-species transmission is increasing as climate changes and humans move to areas where they interact more with animals that were once geographically isolated.
“So we’ve seen, say, in the last 20 years, more outbreaks are associated with zoonotic diseases than we saw in the last 20 years.”
This includes swine flu pandemics caused by the H1N1 virus and associated 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 major force in cross-species transmission of viruses “which would undoubtedly have a negative impact on human health and pandemic risk”.
In a world that has already passed 1C degree of global warming, the authors caution that much of the cross-species viral sharing has already occurred.
Mike Ryan of the World Health Organization warned earlier in the month that rapidly changing weather conditions, such as droughts, exacerbated by climate change, are prompting animals and humans to change their behaviour.
Dr Ryan pointed to recent monkeypox outbreaks, an upward trend in cases of Lassa fever, spread by the common African rat, and the increasing frequency of Ebola outbreaks.
“So, I think that’s a lesson, these diseases will continue to emerge, they will continue to push, they will continue to cross the species barrier,” he said.
“The question is: are we in a position to answer collectively?”
There are opportunities for customization
Of course, as the world continues to warm, we need to be prepared for the direct health effects of that heat.
“The heat is going to affect our health in many different ways,” says Dr Osborne from the University of Queensland.
The IPCC expects that between 2030 and 2050, climate change will cause about 250,000 additional deaths per year from malnutrition, malaria, diarrhea and heat stress.
Australia may initially escape the brunt of these challenges, with countries with more widespread poverty more likely to be affected first, but will not be completely spared.
But amidst all the doom and gloom, there are some glimmers of optimism.
Scientists are working hard to find ways to reduce the risk of health consequences from environmental change, including the newly created Australian HEAL Network, of which Dr Osborne is a member.
The IPCC’s April report found that the world already has the tools to keep global warming below 1.5C. But it warned that there must be “transformative change” immediately if this is to happen.
“I am encouraged by the climate action being taken in many countries. There are policies, regulations and market tools that are proving to be effective. If these are scaled up and implemented more broadly and equitably, they could lead to deeper emissions. can support reduction and encourage innovation,” IPCC chair Hoesung Lee said in April.
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