Around 700,000 people die every year from mosquito-borne disease. The biggest culprit is malaria, but other mosquito-borne diseases, like dengue fever, chikungunya, and Zika, have proliferated wildly in recent years, and now make up a substantial share of the global burden of mosquito-borne disease. By some estimates, the number of dengue infections has increased 30-fold in the past 30 years.
The culprit? Climate change, plus urbanization and changes in where human populations are concentrated. And a new study in Nature Microbiology suggests that things will only get worse. Using statistical mapping techniques, they model how two disease-carrying mosquitos, Aedes aegypti and Aedes albopictus, have spread over the last 30 years, and predict how they’ll spread over the next 30.
The results are alarming. These species of mosquito — which carry infectious diseases including Zika, dengue, chikungunya, and yellow fever, though not malaria — are expected to spread throughout most of the United States and Europe, exposing hundreds of millions of people to these diseases.
“Overall,” the study finds, “our predicted expansions will see Ae. aegypti invading an estimated 19.96 million km by 2050 (19.91–23.45 million depending on the climate and urbanization scenarios), placing an estimated 49.13% (48.23–58.10%) of the world’s population at risk of arbovirus transmission.”
The expanding range of disease-transmitting mosquitos is a significant source of harms from climate change. These diseases largely have low mortality, but serious quality-of-life costs (in the case of Zika, brain damage in fetuses). It’s not clear that most countries are ready to address the public health challenge.
What’s driving the spread of mosquitos?
Modeling which parts of the world will be affected by mosquitos is tricky, in part because lots of factors affect their spread.
Climate change, of course, has vastly expanded the range of possible suitable habitats for many species of mosquito. Urbanization has, too. The paper argues that in the past, projections of mosquito spread were overly simplistic: “Those projections assumed that both species can fully infest all areas of predicted newly suitable habitat.”
In reality, it’s more complicated than that. Ae. aegypti, particularly, has a short flight range, and on its own would take centuries to expand the range of its habitat. It has mostly expanded through shipping: Mosquito eggs can catch a ride in tires and potted plants.
That means that urbanization, shipping, and adaptation among the mosquito species to new conditions all play a role in the spread of mosquitos. It’s not sufficient to check whether a location will be habitable to them, argues the study — researchers also need to think about how quickly mosquitos will reach and colonize the area.
The authors solved this with a mathematical model that made use of statistics, especially in the US and Europe, on mosquito spread so far. They found that urbanization, shipping, and human activity will be the most relevant drivers of mosquito spread at first. Later, it’ll be climate.