Scientists have long warned that climate change would push species into new territories, with the advance of disease-carrying mosquitoes among their biggest concerns.
But this is not a theoretical future threat. Mosquitoes that transmit malaria have been roaming warmer areas of Africa for over a century, according to a new study.
Georgetown University biologist Colin Carlson and his colleagues used one of the most comprehensive datasets ever compiled by medical entomologists to track the spread of mosquitoes in Africa over 120 years.
The data allowed the researchers to estimate the range limits of 22 species anopheles Mosquitoes between 1898 and 2016. In that time, the world has warmed by at least 1.2 degrees Celsius, opening up new areas suitable for mosquitoes.
As a result, anopheles Mosquitoes have spread 4.7 kilometers (almost 3 miles) south each year and have risen 6.5 meters in height each year.
That’s further and faster than estimates from a 2011 study, which reported that terrestrial species were generally moving 1.1 miles (1.7 km) a year poleward and 1.1 meters (3.9 ft) uphill — a rate about two to three times higher at the time was faster than previously thought.
In fact, this new study suggests that Africans anopheles Mosquitoes have moved so far that they are now found, on average, 500 kilometers (310 miles) closer to the South Pole and 700 meters (2,300 feet) further uphill than at the turn of the century.
According to Carlssonthis is some of the first “hard historical evidence” that mosquitoes are already on the move with rising temperatures – and have been for quite some time.
“This is exactly what we would expect if climate change helps these species reach colder parts of the continent,” says Carlson.
“Up to this point,” Carlson tells Science Alert, “most work on climate change and malaria has focused on the dynamics of malaria transmission itself. Here we take a step back and say that climate change could independently affect mosquitoes and mosquitoes.” before we even get to the malaria part of the story.”
Mosquitoes are fleeting: they can travel hundreds of kilometers overnight on wind currents. But these cold-blooded creatures are also sensitive to temperature fluctuations, humidity, and precipitation, so local climates dictate where they can survive.
Climate change is expected to not only expand the range of mosquitoes, but also increase the time they are in effect each year.
Note that this new study only tracked mosquitoes in the genus anophelesCarlson says other mosquito species likely move in similar ways, but only by collecting data can we begin to understand how far they might go.
“We tend to assume that these shifts are happening all around us, but the evidence base is pretty limited,” says Carlson.
As for anopheles Mosquitoes, tracing their spread throughout history, could help explain the changing patterns of malaria transmission in the African region. It could also help clarify long-standing debates about why malaria cases have risen specifically in the East African highlands.
Some researchers have argued that the malaria resurgence in the highlands is better explained by lapsed control programs and growing drug resistance, while others say rising temperatures are part of the powerful mix of factors affecting malaria transmission that we need to recognize.
“If (anopheles) mosquitoes are spreading in these areas for the first time,” argues Carlson, then “it may help explain some recent changes in malaria transmission that are otherwise difficult to attribute to climate.”
All of this information plays an important role in allocating health resources, which researchers say should be channeled to the edges of transmission zones, where health systems may not be adequately prepared to deal with the increasing risk of the disease.
Of course, we don’t just have to worry about malaria. This is what Carlson’s earlier research shows aedes Mosquitoes — carriers of dengue, chikungunya, and zika viruses — are also on the move.
In the worst case, almost a billion people could be at risk of virus retransmission aedes Mosquitoes as the planet warms to add to the billions more at risk from malaria.
However, less is known about the effects of climate change aedes mosquitoes than on anopheles Therefore, the best way we can manage the changing situation is with increased surveillance to monitor disease outbreaks.
“We should look for species that are moving,” Carlson tells ScienceAlert, “and think about how we’re preparing for the health impacts of climate change.”
The research was published in biology letters.