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Mosquitoes living in fragmented forest habitats are increasingly feeding on human blood as wildlife populations decline, a shift that scientists say could heighten the global risk of mosquito-borne diseases amid accelerating environmental degradation.
The finding comes from a recent study conducted in remnants of Brazil’s Atlantic Forest, one of the world’s most biodiverse yet heavily degraded ecosystems. The research, titled “Aspects of the blood meal of mosquitoes (Diptera: Culicidae) during the crepuscular period in Atlantic Forest remnants of the state of Rio de Janeiro, Brazil,” was published in Frontiers in Ecology and Evolution in January 2025.
Researchers analyzed the blood meals of mosquitoes captured during twilight hours in two forested areas in Rio de Janeiro state: the Guapiaçu Ecological Reserve and Sítio Recanto Preservar. Both sites are surrounded by human-modified landscapes and represent typical examples of forest fragmentation seen across much of the Atlantic Forest biome.
The team, led by entomologist Jeronimo Alencar of the Oswaldo Cruz Institute, collected 1,714 mosquitoes using carbon dioxide–baited CDC light traps. Of those, 145 female mosquitoes were found to contain blood. Genetic analysis allowed scientists to identify the source of the blood in 55 specimens, revealing that humans accounted for the majority of identifiable blood meals.
“Mosquitoes are opportunistic feeders,” Alencar said. “When biodiversity declines and wildlife becomes less available, humans often become the most accessible and predictable source of blood.”
The Atlantic Forest once covered large portions of Brazil’s eastern coastline but has been reduced to a fraction of its original size due to centuries of logging, agriculture and urban expansion. The loss of habitat has driven many vertebrate species into smaller, isolated forest patches, altering ecological interactions that once diluted disease transmission.
In intact ecosystems, mosquitoes typically feed on a wide range of vertebrates, including birds, mammals, reptiles and amphibians. This diversity can limit the transmission of pathogens to humans, a phenomenon known as the dilution effect. Fragmentation disrupts that balance, increasing contact between mosquitoes and people.
The study identified several mosquito species known for their flexible feeding behavior, including Aedes scapularis and Psorophora ferox, feeding on humans as well as other animals such as birds, rodents and amphibians. However, the dominance of human blood meals suggested a strong ecological shift driven by environmental pressure rather than innate preference.
“Humans are not necessarily the preferred host,” said Sérgio Lisboa Machado, a co-author of the study and researcher at the Federal University of Rio de Janeiro. “But in fragmented landscapes, they often become the most available host.”
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Implication to The World
Public health experts say the findings have implications far beyond Brazil. Fragmented habitats are increasingly common across the tropics, from Southeast Asia to Central Africa, where deforestation, road construction and agricultural expansion are reshaping ecosystems at unprecedented speed.
Mosquitoes are vectors for a wide range of viruses, including dengue, Zika, chikungunya and yellow fever. Increased human exposure at the edges of degraded forests raises the risk of both endemic transmission and spillover events, in which pathogens circulating in wildlife populations jump to humans.
“Environmental change is a major driver of emerging infectious diseases,” said Alencar. “What we observe in the Atlantic Forest may be occurring in many other regions experiencing similar patterns of habitat loss.”
The study focused on the crepuscular period, when many mosquito species are most active and human outdoor activity often increases. This overlap further amplifies the risk of mosquito-human contact in forest-edge environments.
Researchers emphasize that the shift toward human blood meals does not mean mosquitoes are evolving new preferences. Instead, it reflects the erosion of ecological buffers that once separated humans from disease cycles in wildlife.
As forest fragments become smaller and more accessible, people working, living or traveling near them face growing exposure. Scientists warn that conservation policies and public health strategies must be better aligned to address these interconnected risks.
“Protecting biodiversity is not only about saving species,” Machado said. “It is also about protecting human health by maintaining ecological systems that regulate disease transmission.”
The authors argue that restoring forest connectivity, limiting uncontrolled land conversion and strengthening mosquito surveillance in fragmented landscapes could help reduce future disease risks. Without such measures, they warn, environmental degradation may continue to undermine natural barriers that have long shielded humans from vector-borne diseases.
The study adds to a growing body of evidence linking ecosystem disruption to public health threats, reinforcing calls for conservation efforts that recognize the close ties between environmental integrity and human well-being.
As habitat fragmentation accelerates worldwide, the researchers caution that mosquitoes turning to human blood may become an increasingly common — and dangerous — consequence of environmental neglect. (Wage Erlangga)
