[Aedes aegypti] is responsible for spreading Zika, dengue, yellow fever, and chikungunya in various regions around the world. Although A. aegypti currently inhabits many cities around the world, it originated as a forest-dwelling species in Africa. A group of researchers sought to understand how this transition happened and, more specifically, how the mosquito evolved a preference for human hosts.
The researchers from Princeton University identified two major factors: a dry climate and city life.
“Mosquitoes living near dense human populations in cities such as Kumasi, Ghana, or Ouagadougou, Burkina Faso, showed increased willingness to bite human hosts,” noted Noah Rose, PhD, a postdoctoral fellow in the McBride lab. “But they only evolve a strong preference for human hosts in places with intense dry seasons—in particular, in the Sahel region, where rainfall is concentrated in just a couple months out of the year. We think this is because mosquitoes in these climates are especially dependent on humans and human water storage for their life cycle.”
The researchers say that climate change in the next few decades isn’t expected to drive major changes to the dry season dynamics they found were important to mosquitoes. But, they say, rapid urbanization could push more mosquitoes to bite humans in many cities across sub-Saharan Africa over the next 30 years.