Stretching along the Brazilian coastline, the Atlantic Forest is home to hundreds of species of birds, amphibians, reptiles, mammals, and fishes. However, due to human expansion, only about a third of the forest's original area remains intact. As human presence drives animals from their habitats, mosquitoes that once fed on a wide variety of hosts might be finding new, human targets to quench their thirst for blood, a new Frontiers in Ecology and Evolution study found.
"Here we show that the mosquito species we captured in remnants of the Atlantic Forest have a clear preference for feeding on humans," said senior author Dr Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Rio de Janeiro.
"This is crucial because, in a environment like the Atlantic Forest with a great diversity of potential vertebrate hosts, a preference for humans significantly enhances the risk of pathogen transmission," added co-author Dr Sergio Machado, a researcher who studies microbiology and immunology at the Federal University of Rio de Janeiro.
Humans preferred
For their study, the researchers used light traps to capture mosquitoes at the Sítio Recanto Preservar and the Guapiacu River Ecological Reserve, two natural reserves in the state of Rio de Janeiro. In the lab, engorged female mosquitoes were separated for analysis. The researchers extracted DNA from the blood and used DNA sequencing to analyze a specific gene that functions as a unique 'barcode' for each vertebrate species. By comparing barcodes found in the blood to a database, the researchers could determine which animal the mosquito had fed on.
Out of a total of 1,714 captured mosquitoes belonging to 52 species, 145 females were engorged with blood. Blood meals consumed by 24 of those mosquitoes could be identified and were sourced from 18 humans, one amphibian, six birds, one canid, and one mouse. Some blood meals were made up of multiple sources: the meal of a mosquito identified as Cq. Venezuelensis was made up of amphibian and human blood. Mosquitoes belonging to the species Cq. Fasciolata had fed on both a rodent and a bird as well as a bird and a human, respectively.
The researchers hypothesized that multiple factors could play a role in their preference for our blood. "Mosquito behavior is complex," Alencar said. "Although some mosquito species may have innate preferences, host availability and proximity are extremely influential factors."
Disease spreads
As the Atlantic Forest dwindles due to deforestation and humans keep pushing into previously forested areas, many plants and animals disappear. As a result, mosquitoes change their habits and habitats and get closer to humans. "With fewer natural options available, mosquitoes are forced to seek new, alternative blood sources. They end up feeding more on humans out of convenience, as we are the most prevalent host in these areas," explained Machado.
Bites are more than itchy. In the study regions, mosquitoes transmit a variety of viruses – such as Yellow Fever, dengue, Zika, Mayaro, Sabiá, and Chikungunya – which cause diseases that seriously threaten human health and can have long-term adverse consequences. Investigating mosquito foraging behavior is fundamental for understanding the ecological and epidemiological dynamics of the pathogens they transmit, the researchers said.
The relatively low rate of engorged mosquitoes – just under 7% – as well as the low percentage of cases in which blood meals could be identified – around 38% – highlight the need for more data rich studies. Those studies should also use methods more suited to identifying mixed blood meals to determine all food sources.
Already, the study can aid in the development of more effective policies and strategies to control disease-carrying mosquitoes and help predict and prevent future disease outbreaks. "Knowing that mosquitoes in an area have a strong preference for humans serves as an alert for transmission risk," Machado pointed out.
"This allows for targeted surveillance and prevention actions," concluded Alencar. "In the long term, this may lead to control strategies that consider ecosystem balance."
