How climate change could make infectious diseases even more difficult to combat in the future

• The COVID-19 pandemic has been one of the deadliest virus outbreaks in modern history.
• But researchers fear this pandemic could only be the beginning of a new battle against infectious disease outbreaks — the World Health Organization warns that climate change could make the spread of disease even worse in the coming decades.
• Researchers worry that rising temperatures could cause animals to spread disease in more widespread areas, make pathogens more savvy at surviving in hot climates, and possibly weaken the human body's immune response.
• Though today's novel coronavirus pandemic has not specifically been linked to climate change, here's what could be in store for the future.
• Visit Business Insider's homepage for more stories.

Today's novel coronavirus has wreaked havoc on the globe.

The pandemic has rapidly uprooted life as we know it and left countries across the world scrambling to contain the outbreaks. In just a few short months, billions of people have become jobless, ill, or had their lives significantly disrupted.

But this might not be the only infectious disease we'll have to battle in our lifetimes.

According to research from the World Health Organization, and other institutions, the threat of climate change could make outbreaks even worse in the coming decades.

Researchers fear that as temperatures continue to rise, infectious-disease carrying animals could adapt to more widespread climates, pathogens could become stronger at surviving in hotter temperatures, and the human immune system could face greater difficulty in battling illness.

Though the COVID-19 pandemic has not been linked to climate change, here's how rising global temperatures could lead to an increase in future infectious diseases.

Research about climate change and the spread of infectious disease is complex, multi-factorial, and unfolding in real-time. According to the WHO, "Changes in infectious disease transmission patterns are a likely major consequence of climate change," but there's still a lot that we don't know.

Examples of how climate change could affect the spread of infectious disease.      World Health Organization

Source: WHO

There's no evidence to suggest the COVID-19 pandemic was sparked by climate change. Research pinning certain events to climate change takes more time to complete.

Residents wait to be given access to shop in a supermarket in small groups of forty people on February 23 in the small Italian town of Casalpusterlengo.      Miguel Medina/AFP via Getty Images

Sources: Time Magazine, Johns Hopkins

"Epidemic challenges are becoming increasingly numerous, and there's no reason to think that this is the most severe challenge that would emerge in our lifetime," Frank Snowden, a Yale professor emeritus in the history of medicine, and author of the book "Epidemics and Society: From the Black Death to the present," previously told Business Insider when discussing the coronavirus.

FILE - In this April 16, 2020 file photo, medical staff tend to a patient in the emergency COVID-19 ward at the San Carlo Hospital in Milan, Italy. As Italy prepares to emerge from the West’s first and most extensive coronavirus lockdown, it is increasingly clear that something went terribly wrong in Lombardy, the hardest-hit region in Europe’s hardest-hit country. By contrast, Lombardy’s front-line doctors and nurses are being hailed as heroes for risking their lives to treat the sick under extraordinary levels of stress, exhaustion, isolation and fear. (AP Photo/Antonio Calanni, file)      Associated Press

Source: Business Insider

But further studies would be needed to understand whether or not this is conclusive. Researchers do, however, largely agree that climate change disrupts patterns within nature that could either lead to an increase in disease outbreaks or the difficulty in combating them.

Medical personnel move a deceased patient to a refrigerated truck serving as make shift morgues at Brooklyn Hospital Center on April 09, 2020 in New York City.      ANGELA WEISS/AFP via Getty Images

Source: Scientific American

Additional research by a group of scientists in Tokyo found that mice exposed to warmer temperatures were less effective at fighting off an influenza virus. The research suggested that warmer climates could possibly lead to a weakened immune system.

Flickr/Renee Germany

Source: Scientific American

This trend could continue as the planet warms and pathogens that survive in warmer temperatures reproduce to become better adapted to changes in climate.

A block of ice from the Pastoruri glacier melts as tourists visit the glacier in a tour called "Route of climate change" in Huaraz, Peru.      Gian-Reto Tarnutzer/Unsplash

Source: Time Magazine

Casadevall and a team of researchers found an example of this happening in a drug-resistant fungus. The researchers found that the fungus was able to emerge on three different continents due to its ability to withstand similar temperatures.

Rocky Houghtby/Flickr

Source: Scientific American

"Imagine that the world is hotter and that lizards adapt to live in temperatures very close to yours. Then their viruses adapt to higher temperatures," Arturo Casadevall, chair of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health, told Scientific American. "We have two pillars of defense: temperature and advanced immunity. In a warming world, we may lose the pillar of temperature if the [pathogens] adapt to be close to our temperature."

redcupt2/flickr

Source: Scientific American

For example, bats — the suspected vector for the COVID-19 pandemic — can maintain body temperatures as high as 105 degrees Fahrenheit. This means that they could carry with them a set of pathogens that their body heat can withstand, but that humans, who maintain a resting body temperature of 98.6 degrees Fahrenheit, could not.

grey-headed Flying-fox (Pteropus poliocephalus), a native Australian bat, stretches its leathery wings as it flies high over Sydney's Botanical Gardens      GREG WOOD/AFP via Getty Images

Source: Time Magazine, Business Insider

But as temperatures warm around the globe, viruses are increasingly getting better at adapting and surviving in hotter environments — including within our bodies.

NASA.gov

Source: Time Magazine

One way the human body works to fight off disease is by increasing our internal temperature, known as a fever. When a pathogen enters the body, we often develop a fever in order to stimulate our immune system and create a climate where pathogens can't survive.

A woman has her body temperature checked amid the coronavirus outbreak.      AP Photo/Vincent Thian

Source: Time Magazine

But an increase in the spread of disease isn't the only way climate change could impact future epidemics. Warming temperatures might also make our natural immune systems less effective at fighting off pathogens.

Diagram of the human immune system.      Shutterstock

Sources: Time Magazine, Scientific American

A 2017 study found that land mammals are moving toward cooler climates at an average rate of about 10 miles per decade, while marine species are moving at about 44 miles per decade.

Zolla Chen/Shutterstock

Sources: Scientific American, Science

Scientists have also noted that as temperatures continue to rise, animals have begun migrating to typically cooler environments. This could open up new pathways of disease transmission between animals, since more species will likely begin interacting with one another.

Associated Press

Source: Scientific American

Deforestation could also play a role in the spread of disease. According to the US Agency for International Development, 75% of new or re-emerging diseases at the start of the 21st Century have been transmitted from animals, often because deforestation has brought them closer to human environments.

Aerial photo of deforestation in Malaysia rainforest.      Shutterstock

Source: Columbia University

And since climate change is expected to cause an increase in food scarcity, more people in Africa may consume bushmeat, which have been attributed to nearly 50% of Ebola outbreaks in the past.

A woman displaced by the recent wave of floods in Konto Karfi, prepares to roast bushmeat at an outdoor facility of an Internally displaced people (IDPs) camp in Otokiti, Kogi State, on September 19, 2018      SODIQ ADELAKUN/AFP via Getty Images

Source: Columbia University

Some researchers believe that weather events play a role in Ebola outbreaks, since dry seasons followed by plentiful rainfall can lead to an increase in fruit production, which could create an environment for animals to feed together and spread the disease.

Two bats eating fruit together.      Shutterstock

Source: Columbia University

Similarly, diseases that are transmitted from animals to humans, such as rats or ticks, have been known to shift depending on climate conditions. Certain rodent-borne diseases are linked to flooding, which is expected to become worse as global temperatures rise.

A rat stands on a cement block in a flooded street after a heavy downpour of rain and hail at Besiktas near Istanbul on July 27, 2017.      BULENT KILIC/AFP via Getty Images

Source: WHO

Erin Mordecai, a Stanford biologist studying warming climate and infectious disease, warned that "If the climate is becoming more optimal for transmission, it's going to become harder and harder to do mosquito control." She added: "It's coming for you."

Anopheles stephensi mosquito feeding on a human host, droplet of blood expelled from the mosquito abdomen, close-up view.      Smith Collection/Gado/Getty Images

Source: Stanford University

Researchers fear that as the planet warms, mosquitoes will be able to breed more rapidly and spread disease in typically cooler areas of the world that have otherwise remained unaffected by the pests.

As the climate warms, these two species of mosquito will expand farther and farther from the tropics.      TT/Getty

Source: Stanford University

The risk for malaria epidemics can increase five-fold after an El Niño event, a weather pattern that's expected to get worse with climate change.

A worker of Anglogold Ashanti Malaria Ltd sprays the walls of a house with insecticide against mosquitoes during a Malaria outbreak.      CRISTINA ALDEHUELA/AFP via Getty Images)

Sources: WHO, NOAA

Since the early 19th century, the Punjab region of India has experienced malaria epidemics due to an increase in monsoons and humidity, which provide good conditions for mosquito breeding.

An Indian fruit vendor, Bhupinder Sethi sits on a flooded street as he waits for customers near the bus stand in Punjab.      STR/AFP via Getty Images

Source: WHO

For example, researchers have known that higher temperatures and wetter climates can can lead to an increase in mosquito-transmitted diseases such as malaria.

Close-up of a mosquito sucking blood from a human.      Shutterstock

Source: WHO

As global temperatures continue to rise and create changing weather patterns like increased rainfall, natural disasters, and extreme heat waves, there could be an increase in the ideal environments needed to spread some types of infectious disease.

A view of the flooded Delhi Zoo, where Aedes mosquito larvae have been found at various places.      Parveen Negi/The India Today Group via Getty Images

Source: WHO

Infectious diseases can spread in multiple ways: from humans to humans, from animals to humans, and from a vector like mosquitoes, for example.

An illustration showing an example of human-to-human disease transmission.      World Health Organization

Source: WHO