As global temperatures have gone up, so too have outbreaks of many infectious illnesses. Climate change has exacerbated 218 out of 375 conditions
Climate change is constantly in the news these days and for good reason. The report published earlier this year by the Intergovernmental Panel on Climate Change (IPCC), representing the opinion of 234 expert scientists from 195 counties, made for sobering reading. We are due to pass a key threshold by 2040 which will have catastrophic consequences for humanity.
That threshold is a 1.5C rise in the global average temperature above pre-industrial levels. The report states that “It is unequivocal that human influence has warmed the atmosphere, ocean and land.” It also stated that we are close to a tipping point, where we will have gone beyond the point where we can reverse the trajectory towards hugely negative consequences for life on earth, including us.
More promisingly, the IPCC report listed a range of things we can do to make sure we don’t reach the tipping point and the inexorable rise in temperature. We must replace fossil fuels as soon as possible and move to renewable sources of energy. We must also change our dietary habits, since the livestock industry is a huge contributor to global warming. And thirdly we must make our cities much more environmentally friendly. Each of these is very challenging but there’s no mistaking what needs to be done.
We’re also by now all familiar with what could happen if we don’t reverse global warming. There’ll be more and longer periods of extreme weather which are highly disruptive and damaging. Forests will also die, which exacerbates global warming because trees are major sinks for carbon. And we all know the risk from sea levels rising because of melting ice caps, leading to widespread flooding, especially in poorer countries which are especially vulnerable, leading to the mass migration of people and all that entails.
There is another consequence of global warming, however, as if these issues weren’t enough to be going on with. You may be less aware of this but it’s an important one. There will be a rise in the incidence of a whole range of diseases. As global temperatures have gone up, so too have outbreaks of many infectious diseases.
Mosquitoes are now thriving in areas where they hadn’t previously and this is because of increased temperatures
Scientists have concluded that climate change has made more than 200 infectious diseases worse. In a report titled ‘Over Half of Known Human Pathogenic Diseases can be Aggravated by Climate Change’, published in Nature Climate Change, by lead author Camilo Mora from the University of Hawaii, they scoured the scientific literature for any evidence of how features of climate change, including increasing temperature, a rise in sea level and droughts affect infectious diseases. They included infections caused by bacteria, viruses, insects and fungi. More than 77,000 reports were studied with most of the studies being published after 2000, when interest in this particular aspect of climate change began to grow.
What they found was striking. Climate change has exacerbated 218 out of 375 infectious diseases. But it went beyond that, because they also noted how diseases not caused by infection, such as asthma or poisonous bites from snakes and insects, also got worse because of climate change.
Why might this be? The scientists found the main reason for infectious diseases spreading more is because the germs that cause disease are coming into contact with humans more frequently. A good example is Lyme disease. This is a painful disease caused by tick bites. Ticks are tiny blood-sucking insects which usually jump from small mammals or birds onto us. When the tick bites, it passes a bacteria called borellia into us, which then causes an inflammatory condition not unlike arthritis, but also causes severe fatigue and headaches that can persist for months.
Lyme disease remains difficult to treat. As global temperatures rise, the animals the ticks live on can move into new habitats and so bring the disease with them. Lyme disease has now been reported as far north as Canada and even Nova Scotia, into areas that were previously too cold for the ticks to survive. Neither of these places had reported cases of Lyme disease before 2002.
There are many insect-borne diseases, not least malaria, which is spread by mosquitoes. They are also thriving in areas where they hadn’t previously, because of increased temperatures. It’s also been found that they are active for longer, wherever they may be, with one study showing activity has increased 39pc between the 1950s and the 2010s.
This almost doubles the risk of us catching malaria from mosquitoes. We still have no vaccine for malaria although there has been progress. The mosquito is also the source of other nasty diseases with names like dengue fever and chikungunya. Higher temperatures were found to increase the survival and biting rates of mosquitoes carrying West Nile virus. That virus is rarely fatal but causes symptoms which include joint pain, headaches, vomiting and diarrhoea.
And then there are bats. We are all only too familiar with the global catastrophe they caused when they were shown to be the source of the SARS-CoV-2 virus that caused Covid-19. They are also moving into areas where they previously couldn’t survive, and that again is being put down to increasing temperatures. This means a greater chance of them encountering us and passing on viruses.
Overall, the evidence points to the fact there is a lot more mixing of animals and humans going on, perhaps more than in any time in our history. And that will only increase as temperatures continue to rise.
The scientists also found that heatwaves draw more people to water-related activities. This increases the risk of water-borne diseases such as gastroenteritis, which causes diarrhoea and vomiting. It is often caused by bacteria or viruses in the water, including the well-known norovirus or winter vomiting bug, which is something of a misnomer as it can also strike in summer.
They also recorded how storms and floods forced people to move. The people bring diseases such lassa fever, cholera and typhoid fever with them. These infectious diseases are preventable with vaccines or treatable with antibiotics, but they can still cause a lot of illness, and can be dangerous for vulnerable people.
Finally, the scientists reported an increase and worsening in symptoms of asthma. This could be due to pollution levels rising but was also most likely due to an increase in allergens being released by plants and fungi. An asthma attack can be provoked by pollen or other plant products. An increase in temperature has been linked to more pollen release, which will in turn increase asthma. Remember when the pollen count was announced on the radio? We may well need to go back to that to warn people.
The authors of this important study conclude there’s no part of global health that climate change isn’t affecting. They also remind us of the economic cost of infectious diseases, mentioning that by some estimates the Covid-19 pandemic cost the US economy $16tn.
It’s a very important study because it tells us it won’t just be rising sea levels or more storms that will harm us. It will also be a whole range of diseases. This gives our species, which is under siege from infectious agents, more incentive, as if we needed it, both for our health and our economies. We need to halt global warming as soon as we possibly can.
Luke O’Neill is professor of biochemistry in the school of biochemistry and immunology at Trinity College Dublin
Full article taken from Irish Independent:
