Scientists researching mosquitoes in a forest region in Brazil have found that the insects there may have an increasing thirst for human blood, raising concerns about an increased risk of virus transmission. The study, published in the journal Frontiers in Ecology and Evolution, involved researchers analysing blood meals of mosquitoes captured in the Atlantic Forest biome in Rio De Janeiro state to learn more about their feeding habits.

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  Scientists used light traps to capture mosquitoes at two natural reserves in the state, Sítio Recanto Preservar and the Guapiacu River Ecological Reserve. They then used DNA sequencing to establish which animals engorged female mosquitoes had fed on, according to a Frontiers press release detailing the study.

The team found that most blood of the blood meals they could identify contained human blood. Out of 1,714 captured mosquitoes belonging to 52 different species, 145 females were engorged with blood. Blood meals consumed by 24 of them could be identified and were sourced from 18 humans, one amphibian, six birds, one canid, and one mouse, with some blood meals made up of multiple sources.

The forest is home to rich array of wildlife including hundreds of species of birds, amphibians, reptiles, mammals, and fishes. However, due to human expansion, which drives animals from their habitats, only around a third of the forest’s original area remains intact.

Researchers believe as a result, mosquitoes that would once have targeted a wide variety of creatures to feed on may be finding new human targets.

Dr Sergio Machado, a researcher who studies microbiology and immunology at the Federal University of Rio de Janeiro and a co-author of the research explained: “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,” he added.

Male and female mosquitoes primarily feed on nectar and plant juices but females also drink blood, using it as a source of protein to produce eggs and reproduce.

This involves biting hosts, which is often harmless, but in the study regions, mosquitoes transmit a variety of viruses including Yellow Fever, dengue, Zika, Mayaro, Sabiá, and Chikungunya, which cause diseases that seriously threaten human health and can even be deadly.

Senior author Dr Jeronimo Alencar, a biologist at the Oswaldo Cruz Institute in Rio de Janeiro said: “Here we show that the mosquito species we captured in remnants of the Atlantic Forest have a clear preference for feeding on humans.”

He says the finding is “crucial” as in an environment like the Atlantic Forest with “a great diversity of potential vertebrate hosts, a preference for humans significantly enhances the risk of pathogen transmission”, but the authors stress that the preponderance of human blood discovered may be due to various factors, and doesn’t neccessarily mean mosquitoes are specifically targetting humans over other animals.

These circumstances could see mosquitoes transmitting more viral diseases and adverse health outcomes for people who live in the area.

The team believe research such as that which they have carried out can contribute to better prevention actions.

Hypothesing on why the creatures appear to be targeting humans more, Dr Alencar said: “Mosquito behavior is complex.

“Although some mosquito species may have innate preferences, host availability and proximity are extremely influential factors.”

The study notes 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%) points to the need for more data rich studies, which should also use methods more suited to working out all food sources in mixed blood meals.

Nevertheless, Dr Machado says: “Knowing that mosquitoes in an area have a strong preference for humans serves as an alert for transmission risk.”

Dr Alencar: “This allows for targeted surveillance and prevention actions. In the long term, this may lead to control strategies that consider ecosystem balance.”