As deforestation and habitat loss drive down wildlife populations, mosquitoes are increasingly turning to another source for their blood meal: humans. That’s the finding of a new study in Brazil’s Atlantic Forest, a global biodiversity hotspot with less than a third of its original forest remaining.
Mosquitoes in the Atlantic Forest “have a clear preference for feeding on humans,” senior author Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Rio de Janeiro, said in a statement.
To reach that conclusion, researchers collected 1,714 mosquitoes from two different Atlantic Forest reserves in the Brazilian state of Rio de Janeiro. Only female mosquitoes bite; they require a blood meal to develop their eggs, so researchers focused on the 145 engorged female mosquitoes they collected. Of those, just 24 contained blood that could be successfully analyzed and matched to known vertebrates using DNA analysis.
Three-quarters of the samples, 18 of the 24, revealed that the mosquitoes had fed on humans. The other sources of blood came from six birds, one amphibian, one canid and a mouse. Several mosquitoes had fed on more than one host species, including combinations of human/amphibian and human/bird, further raising concerns about the spread of disease.
Researchers say they believe mosquitoes are showing a preference for human blood because deforestation and habitat loss have reduced the number of wild animals available for mosquitoes to feed on.
“Once the vertebrate population decreases, moving for other habitats, mosquitoes … go in search of new blood sources,” Sérgio Lisboa Machado, a co-author of the study with the Federal University of Rio de Janeiro, told Mongabay in an email. In this case, the new blood source is human.
The Atlantic Forest once covered roughly 1.3 million square kilometers (502,000 square miles) along the east coast of Brazil and extending into Argentina; that’s an area larger than Peru. Today, less than 30% of the forest remains, much of it heavily fragmented and surrounded by human settlements, agriculture and roads.
As further deforestation and habitat loss push mosquitoes toward human hosts, scientists warn the risk of disease could rise. The insects are responsible for roughly a million human deaths globally each year from zoonotic diseases including malaria, yellow fever, Zeka virus and dengue fever.
Rising temperatures due to climate change are also creating more favorable conditions for mosquitoes to breed and spread into new areas. This study adds to a growing body of evidence that deforestation and habitat disruption pose risks for both wildlife and human health.
The researchers conclude that further studies should be conducted to better understand how deforestation is impacting mosquitoes’ feeding choices and the potential impact this will have on public health.
Banner image: A mosquito feeds on a human host. Photo by JJ Harrison via Wikimedia Commons (CC BY-SA 3.0).
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