As climate change continues to drive weather extremes, humans and pathogens are coming in closer contact with each other, more than ever before. There are direct causes of disease — such as warming oceans becoming breeding grounds for certain bacteria — and indirect causes, like stress episodes that can lower one’s immune system. Research now suggests that climate change and infectious diseases are closely related, with global warming estimated to cause the spread of over half the world’s diseases. Here are 5 factors that affect it.
Inhaling smoke causes heart and lung disease, along with worsened cases of asthma or bronchitis. With the respiratory and circulatory systems damaged, people are more likely to develop severe respiratory infections if they catch viruses such as the coronavirus.
One of the consequences of wildfires is the displacement of disease-carrying animals. For example, bats might be driven out and forced to settle on a nearby farm when a fire destroys a forest. By coming in contact with humans or farm animals, they may then spread the disease they are carrying.
This is how the Nipah virus started in Indonesia. Infected bats flew to an orchard bordering a pig farm, contaminating fruit with their feces and saliva. The fruit then fell into the pig pens, the pigs ate it and humans got infected by eating the diseased pigs. With a mortality rate of 40 to 75%, the Nipah virus killed 108 of the 265 people who caught it during that first outbreak.
In 2020, scientists also discovered that wildfire smoke could carry microbes spreading infectious diseases. This new field of study is called pyroaerobiology. Airborne fungi such as coccidiomycoses can spread Valley fever while traveling by smoke, particularly affecting people with compromised immune systems. Bacteria can also travel this way. Since this is a relatively new area of research, scientists still need to collect more data on other types of pathogens.
With few natural water sources available during a drought, mosquitoes often migrate to the water near human dwellings, concentrating in one specific area to breed. The shallow, warm water remaining in lakes and streams is also more likely to harbor amoebas, viruses, and bacteria which can cause deadly diseases.
The heat can cause freshwater algal blooms that may irritate people’s eyes and lungs. At the same time, hot weather drives more people to go swimming. This potentially exposes them to deadly pathogens in the water. People who get their water from private wells are also more at risk of catching a virus during a drought.
With a lack of available clean water, people stop washing their hands. This allows respiratory and stomach illnesses to spread quickly. With no rain to wash away dust and pollen, respiratory diseases also increase due to people breathing in small debris particles.
It is true that droughts kill some pathogens, but not all of them. The ones that survive are more heat-resistant. This means that if a person becomes infected with one of these viruses or bacteria, a fever will not likely destroy it. Like the so-called “superbugs” – pathogens that have become resistant to antibiotics – disease-causing agents that can withstand heat are harder to kill.
During a drought, crops and livestock die, leading many people to starve or go thirsty. Even slight malnutrition opens the door for more severe diseases by suppressing people’s immune systems.
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3. Hurricanes and Tornadoes
Hurricane conditions often force people into cramped shelters. Diseases that spread in close quarters include respiratory illnesses, tuberculosis, and measles.
As the storm destroys sewers and water treatment facilities, rising water levels cause higher instances of water-borne diseases like cholera. The standing water is also a perfect breeding ground for mosquitoes, notable disease carriers.
In the aftermath of a hurricane, many people loose access to medical care because the storm wrecks hospitals, clinics, and pharmacies. Combined with a weakened immune system caused by severe stress, it is no wonder disease outbreaks frequently follow hurricanes.
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During a tornado, damaged power lines often cause electrical failures. Food left in the fridge or freezer spoils quickly under these conditions. Water treatment plants can be damaged as well, making it easy for diseases to spread in the water. And – just as they do during many other natural disasters – people are often forced to squeeze into crowded shelters, making a disease outbreak much more likely to occur
Another reason why climate change and infectious diseases are related are floods, extreme weather events often exacerbated by global warming. Much like hurricanes, floodwaters contain toxic human and livestock sewage. They can also harbour household, industrial, or medical hazardous waste and potentially bring disease-carrying rats to new locations.
Many people are injured by debris when wading through floodwaters and their open wounds can easily get contaminated. Some of the common flood-borne illnesses include cryptosporidiosis, giardia, and norovirus. Getting cut by a fallen piece of metal can also cause tetanus.
Many diseases are spread more easily due to the high population density and frequent movement of people within a nation as well as internationally. Some diseases, like Ebola and Covid19, resulted in strict travel restrictions aimed at avoiding their spreading on a large scale. However, with travel being now an integral part of modern societies and the global population rising constantly, it is now easier than ever for humans to encounter and spread illnesses.
Climate change has also caused a shift in the range of animals. This means that humans are more frequently encountering animals who may spread diseases, such as the case of monkeypox and aviation influenza.
Climate Change and Infectious Diseases: Final Thoughts
Climate change exacerbates extreme weather events. The resulting damage from floods, wildfires, and other natural disasters can allow diseases to run rampant. These events also destroy infrastructure that would usually protect people, such as hospitals and water treatment facilities. Rather than treating these disasters on a case-by-case basis, people must take action to stop climate change so these do not happen or spread in the first place.
EO’s Position: The latest IPCC report clearly shows that the world is rapidly losing sight of being able to stay under the 1.5C limit of global temperature rise. We need to phase out fossil fuels immediately and scale up renewable energy generation to avoid the catastrophic impacts of climate change. With COP27 2022 coming up in November, governments must take steps to update their Nationally Determined Contributions (NDC) to stall global warming.