As global temperatures have increased in recent years, so has the incidence of infectious diseases. Recent threats to public health include SARS, Zika and West Nile virus, Zika and MERS, Zika and West Nile viruses, COVID-19 and clusters of monkeypox.
That’s no coincidence. A study that was published August 1st in Nature Climate Change, researchers tried to understand the relationship between major environmental changes related to higher greenhouse gas emissions—including global warming, rising sea levels, storms, floods, drought, and heat waves—and the outbreaks of 375 human infectious diseases caused by viruses, bacteria, and other pathogens. Climate change was responsible for 58% of the public-health risks.
“The health impacts of climate change are here,” says Dr. Vishnu Laalitha Surapaneni, assistant professor of medicine at the University of Minnesota. “And they are affecting us right here, right now.”
Viruses and other pathogens aren’t becoming better at living in higher environmental temperatures, scientists say. Instead, it’s more likely that the host animals they infect are affected by changing climates. Increasing global temperatures, for example, mean that the geographic range for many pathogen-carrying animals—including insects like mosquitoes—is expanding rapidly. “As they move around to find better climates, there are more opportunities for viruses to spill over among other mammals, and then from some of those mammals to humans,” says Gigi Gronvall, senior scholar at the Johns Hopkins Center for Health Security at the Bloomberg School of Public Health. These animals transport their microbes to new locations in the same manner that roads, trains, planes and airplanes connect distant parts of the globe.
Tickborne diseases are one example of climate’s impact on human health. Warmer temperatures have made it more difficult for ticks to survive in the north. This includes Canada and Nova Scotia. Lyme disease is a tick-borne illness that was not reported in either place until 2002.
Continue reading: Lyme Disease is a common condition that affects around 15% of the population.
Additionally, dangerous pathogens such as the vibrio Genus flesh-eating bacteria are being allowed to thrive in warmer ocean waters. Infections from these bacteria have recently increased—not only when natural climate disasters such as hurricanes sweep over land and bring contaminated waters in closer contact to people, but also when people with exposed cuts or wounds venture into oceans, which have become fertile waters for bacterial growth. A report by The LancetA group of 43 scientists and experts in climate and health from U.N. agencies and academic institutions analysed metrics on environmental impacts on human health. Vibrio is now thriving on the coast of the United States northeast, up 25% and 4% respectively.
The global warming has led to mosquitoes moving further north than any time before. Diseases they carry, such as dengue, have been reported far outside of their typical tropical areas in places like New York City—and disturbingly, the cases aren’t always from travelers, but often from infected mosquitoes circulating in the region. Other pathogens these insects transport, including the ones responsible for Zika and yellow fever, are also being reported in parts of the world where they haven’t previously been common. They are also responsible for yellow fever and zika. LancetAccording to a report, mosquito activity has been increasing in lower-income countries where it is well documented that they thrive. The increase was 39% from 1950-1959 to 2010-2019.
Although mosquitoes thrive in humid, wet climes they can also be attracted to hotter temperatures that could lead to mosquito-borne diseases like West Nile virus. Under drier drought conditions, birds—one of the animal vectors for mosquitoes—tend to congregate in the scarce areas where water is available, creating the ideal conditions for mosquitoes to find new hosts.
As they adapt to climate change, bats are also expanding their territories. The warmer temperatures prompt them to seek out more suitable climes. Their increased mobility increases the likelihood of interaction with humans and spreads diseases such as coronaviruses. “There is a lot more mixing of populations of animals that haven’t been mixed before,” says Gronvall.
It is important to recognize that all species are affected by the changing behaviors of their habitats and the shifting environment they live in. For better understanding the effects of pathogens on humans, scientists recommend that more research be done into how bacteria and viruses circulate within different animal species. “It’s really hard to build bridges between different communities,” such as the U.S. Centers for Disease Control and Prevention and the Environmental Protection Agency or the Department of Agriculture, Gronvall says. “But we are going to need a much more integrated approach to tackling research questions that everyone agrees are important.”
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