Every mosquito bite is annoying, but some mosquito bites are downright dangerous. In tropical regions, a bite can be the first step to contracting a virus with long-lasting health effects. While people in colder climates don’t usually have to worry as much about mosquito-borne disease, new research published Thursday suggests that their safety may be short-lived.
A paper in PLOS Neglected Tropical Diseases shows that by 2080, nearly one billion more people around the world will be at risk for mosquito-borne diseases due to rising global temperatures. These diseases, which include zika, dengue, and yellow fever, already cause millions of deaths per year.
Scientists already knew that climate change is creating warmer environments where mosquitoes can thrive, increasing the risk of mosquito-borne disease. What’s different about this study, co-author and Georgetown University post-doc Colin Carlson, Ph.D., tells Inverse, is that it show how many people will be put at risk.
“We definitely know that more people are going to be at risk from dengue and viruses like it than are currently,” Carlson says. “So the main result of our study — that nearly a billion people might be exposed to these diseases by one or both mosquitoes by 2080 — is extremely concerning, and almost certainly means more people getting sick globally.”
Carlson’s analysis uses projected global temperatures between 2050 and 2080 to determine the new regions that may become hospitable to two types of mosquitoes: Aedes aegypti, sometimes called the “yellow fever mosquito,” and Aedes albopictus, also called the “Asian tiger mosquito”. These mosquitoes prefer specific temperature ranges that are associated with increases in virus transmission. When temperatures are between 21 and 34 degrees Celsius, Ae. aegypti is at its most dangerous, while Ae. albopictus prefers temperatures between 19.9–29.4 degrees. Celsius.
Already, tropical regions in Africa and Central America spend significant portions of the year in these temperature ranges, which can lead to dangerous and costly disease outbreaks. As global temperatures increase, areas north of those regions will have to grapple with more warmer days, too.
If we stay on our current emissions path, both Europe and North America will see significant increases in exposure as climates drift into the mosquito sweet spot. Carlson predicts that, as early as 2050, 55 million more people will be exposed to viruses carried by Ae. aegypti, and 32.1 million will be exposed to those borne by Ae. albopictus. By 2080, those numbers increase to 62.8 million and 34.7 million, respectively.
The outlook also isn’t great for Europe in 2080, where the largest increases in exposure are predicted. By that time, eastern and western Europe combined will see 380.4 million more people exposed to Ae. aegypti and 376.3 million more exposed to Ae. albopictus.
The flip side to the global warming predicament is that climate change may make the tropical regions where the viruses already thrive too hot for mosquitoes, leading to less exposure. That is not, however, an ideal outcome.
In the Caribbean, every climate scenario results in a decrease in the amount of people exposed to viruses, primarily because changing temperatures drives them out of the viral transmission sweet spot. If the world keeps warming at its current rate, Southeast Asia may see a decrease in exposure by 124.8 million people as well. Of course, this increased warming comes with additional risks, like food shortages and extreme weather events, which will come with their own casualties.
Despite these decreases in regional rates, more people around the world will be exposed to mosquito-borne illnesses overall. This puts even more pressure on scientists trying to find better ways to detect and treat mosquito-borne diseases or even genetically engineer them to disappear altogether.
Carlson adds that “a future where we can eliminate mosquito populations would be a great one for human health,” but we may be just as well-served by combating climate change too. If we can a least slow down the ongoing temperature increase, millions of people in the future may not even be exposed to these viruses in the first place:
“Even though we’re locked in for a certain amount of climate-attributable mortality no matter what,” says Carlson, “we could still save millions of lives by working together to set our planet on the right track.”
Forecasting the impacts of climate change on Aedes-borne viruses—especially dengue, chikungunya, and Zika—is a key component of public health preparedness. We apply an empirically parameterized model of viral transmission by the vectors Aedes aegypti and Ae. albopictus, as a function of temperature, to predict cumulative monthly global transmission risk in current climates, and compare them with projected risk in 2050 and 2080 based on general circulation models (GCMs). Our results show that if mosquito range shifts track optimal temperature ranges for transmission (21.3–34.0°C for Ae. aegypti; 19.9–29.4°C for Ae. albopictus), we can expect poleward shifts in Aedes-borne virus distributions. However, the differing thermal niches of the two vectors produce different patterns of shifts under climate change. More severe climate change scenarios produce larger population exposures to transmission by Ae. aegypti, but not by Ae. albopictus in the most extreme cases. Climate-driven risk of transmission from both mosquitoes will increase substantially, even in the short term, for most of Europe. In contrast, significant reductions in climate suitability are expected for Ae. albopictus, most noticeably in southeast Asia and west Africa. Within the next century, nearly a billion people are threatened with new exposure to virus transmission by both Aedes spp. in the worst-case scenario. As major net losses in year-round transmission risk are predicted for Ae. albopictus, we project a global shift towards more seasonal risk across regions. Many other complicating factors (like mosquito range limits and viral evolution) exist, but overall our results indicate that while climate change will lead to increased net and new exposures to Aedes-borne viruses, the most extreme increases in Ae. albopictus transmission are predicted to occur at intermediate climate change scenarios.