This shift in mosquito behavior could significantly increase the risk of spreading dangerous viruses such as dengue and Zika. The reduction of the Atlantic Forest is leading mosquitoes to increasingly choose humans as their primary food source. This, in turn, could potentially accelerate the spread of diseases carried by these insects and make local communities more vulnerable to epidemics.
The Atlantic Forest, which stretches along the Brazilian coast, is known for its incredible diversity of flora and fauna, including hundreds of species of birds, mammals, amphibians, and fish. However, human activity has caused the forest area to shrink to one-third of its original size.
According to the study, as humans encroach on previously untouched ecosystems, wildlife is gradually displaced, and mosquitoes that once fed on various animals begin to seek blood from humans. "We demonstrated that the mosquitoes we captured in the remnants of the Atlantic Forest clearly prefer human blood," noted lead author Dr. Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Rio de Janeiro.
Co-author of the study, Dr. Sergio Machado, a researcher in microbiology and immunology at the Federal University of Rio de Janeiro, added: "This is important because in such an ecosystem with a large number of potential hosts, a preference for humans significantly increases the risk of pathogen transmission."
To analyze the feeding habits of mosquitoes, the research team set up light traps in two nature reserves in the state of Rio de Janeiro: Sitio Recanto and on the Guapiacu River. Mosquitoes that had recently fed on blood were captured and studied in laboratory conditions. DNA was extracted from the mosquitoes' blood, and the scientists sequenced a specific gene that serves as a biological barcode for various vertebrate species. By comparing these barcodes with reference databases, the researchers were able to identify which animals had been bitten by the mosquitoes.
The study collected 1,714 mosquitoes from 52 different species, among which blood was found in 145 females. The sources of blood were identified in 24 of them, including 18 humans, one amphibian, six birds, one dog, and one mouse. Some mosquitoes fed on the blood of multiple hosts simultaneously; for example, one of them, Cq. venezuelensis, took blood from both a human and an amphibian.
The complexity of mosquito behavior can be explained by several factors. "While some species may have innate preferences, the availability and proximity to hosts play a key role," explained Alencar. With ongoing deforestation and the expansion of human settlements, many species of both plants and animals are disappearing, forcing mosquitoes to adapt by changing their habitats and foraging methods.
The study also revealed gaps in existing data: less than seven percent of captured mosquitoes had traces of blood, and sources were identified in only 38 percent of cases. This highlights the need for more in-depth research using advanced methods to detect mixed blood sources.
Nevertheless, the findings already have practical implications, as they can help develop measures to combat mosquitoes and improve early warning systems for disease outbreaks. "Knowing that mosquitoes in a certain area prefer specific types of blood serves as a warning signal for the population about the risk of infection transmission," summarized Machado. "This opens up opportunities for targeted monitoring and preventive measures," concluded Alencar. "In the long term, this could lead to the development of strategies that consider ecosystem balance."
