Why are striped mosquitoes increasingly interested in human blood?

A new study shows that their tastes have changed, they are increasingly fond of human blood and this means an increased ability to transmit disease.

For a long time, Zebra mosquitoes (Aedes aegypti) have been known to suck blood from humans and transmit dengue, Zika and viruses. But in their " home" of Africa, most of the zebra mosquitoes prefer to suck blood from other animals, such as monkeys and rodents. 

By examining the bite range of midges across Africa, research shows that mosquito populations in arid and densely populated areas prefer to suck human blood. Increasing climate change and urbanization will make this more common, although not everywhere.

Mosquito. (Aedes aegypti).

"This study is significant because the more we understand where and why mosquitoes like to bite humans, the better we will be able to predict and minimize the spread of disease." - According to Law Lawzzak, an evolutionary geneticist at the Wellcome Sanger Institute.

Noah Rose, a postdoctoral fellow working with Carolyn McBride at Princeton University and her African colleagues, collected eggs from zebra mosquitoes from 27 locations in sub-Saharan, from arid steppes to wet jungle. and places with different numbers of residents. Rose used the eggs to hatch in the lab and to test the sucking habits of young mosquitoes. Housed in a plastic box with two protruding tubes, a group of 100 mosquitoes could optionally fly down one of the Rose's forearms at the other end or the tube toward a guinea pig. There is a screen to prevent mosquitoes from biting the above two targets.

He also sequenced the genomes of 389 mosquitoes to see how the blood-sucking preferences were related. Anna Cohuet, a medical entomologist at the French National Research Institute for Sustainable Development in Montpellier, who is not involved in this study, sees this as a huge amount of work.

In a report Rose and her colleagues gave at the Biology of Genomes conference, held online last week and in a preliminary draft in February, mosquitoes have different, consistent preferences for pigs or Guinea pigs depend on where they were collected. The team found that mosquitoes originating from African forests like to suck guinea-pig blood. Those from the Sahel region, the semi-arid belt south of the Sahara, always prefer to suck human blood.

For the rest, the closer they are to their mosquitoes from the Sahel, the more likely they are to bite people. (Sahel mosquitoes spread to the Americas hundreds of years ago along with the slave trade.)

The team also found that population density is related to the taste of midges . The more people crowed, the more blood they suck, Cohuet explained. However, this is not a complete explanation, because mosquitoes are also collected from some deserted towns. Instead, the climate is dry and hot most of the year, with only a brief rainy season in the Sahel, seems to have made mosquitoes suck more human blood. In those places, according to Rose, the breeding of mosquitoes seems to become more dependent on the puddles that people leave or get stuck in the tires.

"Thus, if the pace of urbanization is rapid in these arid regions, the blood-sucking mosquitoes will proliferate," said Elaine Ostrander, a geneticist at the Genome Research Institute. national people said. The possibility of transmitting dengue fever and other infectious diseases related to midges makes Ostrander worried. "That would be extremely terrible," she said.