Mosquitoes may be targeting humans more than other animals, according to a new study, raising concerns that habitat loss is pushing disease-carrying insects closer to people.
Researchers working in Brazil’s Atlantic Forest found that mosquitoes captured deep inside nature reserves showed a striking preference for human blood – a shift they say is likely driven by deforestation and declining wildlife populations.
“It’s only a matter of time before these mosquitoes become adapted to humans,” study co-author Dr Sergio Machado told BBC Science Focus. “And once that happens, I think it will be difficult to reverse the process of them living with us.”
To investigate what mosquitoes in the region were feeding on, the team set up light traps at two sites in the state of Rio de Janeiro – Sítio Recanto Preservar and the Guapiaçu Ecological Reserve.
They then extracted and sequenced DNA from the blood inside female mosquitoes, which feed on blood to develop their eggs, to identify the animals they had bitten.
Of the 145 mosquitoes collected, usable blood samples could be identified in just 24. Machado said many samples were lost because the insects are fragile and were damaged before reaching the laboratory.
Even so, the results surprised the researchers. Around three-quarters of the identifiable blood meals came from humans – an unexpected finding given the limited human presence within the forest.
“This was a big surprise for us,” Machado said. “We were not expecting this, especially because some of the traps were about a kilometre inside the forest.”
The findings suggest the insects may be flying out of forested areas to feed on people living nearby, then returning to the reserves – a journey of several kilometres that is unusual, though not unprecedented, for mosquitoes.
Machado said habitat destruction around the reserves is likely playing a key role. As surrounding ecosystems are degraded, the wild animals mosquitoes would normally feed on become scarcer, pushing the insects to seek alternative hosts.
Add to that rising temperatures linked to climate change, which can speed up mosquito life cycles and extend their breeding season, and conditions increasingly favour species that can exploit human populations.
“Only the more adapted animals are going to survive,” Machado said. “In this case, I think mosquitoes are going to survive, but we might not,” he added, only half-joking.
The shift is worrying because mosquitoes can transmit a wide range of dangerous pathogens, including dengue and Zika viruses.
Dengue, for example, was absent from Brazil for more than two decades before re-emerging in 1981. Since then, around seven million cases have been reported in the country, according to the World Mosquito Program.
Globally, mosquito-borne diseases kill around 1 million people every year.
And while this study focuses on one area deep within Brazil, Machado said a similar pattern is likely playing out all over the world. As forests are destroyed and animal populations shrink, mosquitoes will thrive by shifting to humans, bringing a wealth of diseases with them.
For Machado, the solution is simple: protect the forests. “We can prevent this by offering mosquitoes a good environment in the forests,” he said. “I’m not against humans living in and near forests, but we need an equilibrium between nature and how we live because the way things are going now is not good.”
The team plans to carry on studying the movements of mosquitoes in the Atlantic Forest, and is developing new and improved traps to increase their sample size in future research.
“It’s very important for human beings to monitor these environmental changes, not only of insects, but animals, water – everything,” Machado said. “Our study is only one part of this.”
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