Why mosquitoes’ thirst for human blood is intensifying

By Stephen Beech

Mosquitoes’ thirst for human blood is rising, reveals new research.

Scientists found that some of the blood-sucking insects really are targeting humans more than other food sources.

They say the worrying trend raises the risk of disease transmission.

But it could be a matter of convenience for mosquitoes as biodiversity dwindles and other food sources are displaced, according to the study.

Stretching along the Brazilian coastline, the Atlantic Forest is home to hundreds of species of birds, amphibians, reptiles, mammals, and fish.

But human expansion means only about a third of the forest’s original area remains intact.

As human presence drives animals from their habitats, the new study has found that mosquitoes that once fed on a wide range of hosts might be finding new, human targets to quench their lust for blood.

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."

Co-author Dr. Sergio Machado, a researcher in microbiology and immunology at the Federal University of Rio de Janeiro, said: “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.”

For the study, published in the journal Frontiers in Ecology and Evolution, the research team 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.

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 research team 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 believe that multiple factors could play a role in their preference for our blood.

Dr. Alencar said: “Mosquito behavior is complex.

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

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.

Dr. Machado said: “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."

In the study regions, mosquitoes transmit several potentially deadly viruses to humans – including Yellow Fever, dengue, Zika and Chikungunya.

Scientists say that investigating mosquito foraging behavior is "fundamental" for understanding the ecological and epidemiological dynamics of the pathogens they transmit.

The research team 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 studies that use methods more suited to identifying mixed blood meals to determine all food sources.

But they say their findings can aid in the development of more effective policies and strategies to control disease-carrying mosquitoes and help predict and prevent future disease outbreaks.

Dr. Machado said:. “Knowing that mosquitoes in an area have a strong preference for humans serves as an alert for transmission risk."

Dr. Alencar added: “This allows for targeted surveillance and prevention actions.

“In the long term, this may lead to control strategies that consider ecosystem balance.”