This change in behavior could lead to an increased risk of spreading dangerous viruses such as dengue and Zika.
As the area of the Atlantic Forest shrinks, mosquitoes are increasingly turning to humans as their primary source of blood. This shift may accelerate the spread of mosquito-borne diseases and increase the vulnerability of local communities to disease outbreaks.
The Atlantic Forest, which stretches along the Brazilian coast, is famous for its rich biodiversity, including hundreds of species of birds, mammals, reptiles, and fish. However, a significant portion of this biodiversity has already been lost, as human activity has reduced the forest to one-third of its original area.
With the deepening of human impact on previously untouched ecosystems, wildlife is being displaced, and mosquitoes, which once fed on various animals, are now increasingly seeking food among humans, as shown by the study published in the journal Frontiers in Ecology and Evolution.
“We demonstrated that the mosquitoes we captured in the remnants of the Atlantic Forest primarily prefer humans as a food source,” said lead author Dr. Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Rio de Janeiro.
“This is of great significance, as in an ecosystem like the Atlantic Forest, which is home to many species of vertebrates, a preference for humans increases the risk of pathogen transmission,” added co-author Dr. Sergio Machado, a researcher in microbiology and immunology at the Federal University of Rio de Janeiro.
To study the dietary preferences of mosquitoes, researchers set up light traps in the reserves of Sitio Recanto and the Guapiacu River in the state of Rio de Janeiro. They separated recently fed female mosquitoes and studied them under laboratory conditions.
DNA was extracted from the mosquitoes' blood, and a specific gene, serving as a biological barcode unique to each vertebrate species, was sequenced. By comparing these barcodes with reference databases, the team was able to identify which animals the mosquitoes had bitten.
The traps collected 1,714 mosquitoes of different species, among which 145 females were found to have blood. Researchers were able to identify blood sources in 24 individuals, including 18 humans, one amphibian, six birds, one dog, and one mouse.
Some mosquitoes fed on the blood of more than one host. For instance, one mosquito of the species Cq. venezuelensis took blood from both an amphibian and a human. Others, such as Cq. fasciolata, also exhibited mixed feeding, including combinations of rodents and birds, as well as birds and humans.
Researchers believe that this trend can be explained by several factors. “Mosquito behavior is quite complex,” noted Alencar. “While some species may have innate preferences, the availability and proximity of hosts play a key role.”
With ongoing deforestation and the expansion of human settlements, many species of plants and animals are disappearing. In response to such changes, mosquitoes are moving closer to humans, adapting their feeding habits.
Mosquito bites can pose a serious health threat. In the regions where the study was conducted, mosquitoes carry viruses such as yellow fever, dengue, Zika, Mayaro, Sabia, and chikungunya. These infections can cause long-term complications. Researchers emphasized the importance of understanding mosquito dietary preferences to study the spread of diseases in ecosystems and among populations.
The work also revealed shortcomings in current data: less than seven percent of the captured mosquitoes showed traces of blood during feeding, and sources could only be identified in 38 percent of cases. This indicates the need for larger and more detailed studies, including improved methods for detecting mixed blood sources.
Nevertheless, the results obtained may already have practical value. They could help in developing measures to combat mosquitoes and improve early warning systems for disease outbreaks.
“Knowing that mosquitoes in certain regions prefer specific types of blood signals to people the risk of infection transmission,” added Machado.
“This allows for targeted monitoring and preventive measures,” concluded Alencar. “In the long term, this could lead to the development of control strategies that take into account the ecosystem balance.”
