A new study suggests dry climates and dense human populations are key factors in how mosquitoes have evolved to bite people.

Noting that only a handful of the 3,500 species of mosquito feeds on human blood, researchers at Princeton University set out to determine why certain mosquitoes feed on humans. The World Health Organization named mosquitoes one of the deadliest animals on Earth, citing their ability to carry and spread disease.

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The team studied a variety of mosquito — Aedes aegypti — known to carry ailments that include the Zika virus and dengue fever — and collected samples from 27 sites in sub-Saharan Africa. Through genetic analysis, they found mosquitoes became more likely to feed on humans as population grew denser or more urbanized. This was only in regions with a significant dry season.

Authors of the study, published recently in the scientific journal Current Biology, found that during dry seasons, mosquitoes may rely more on water stored by people.

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The researchers also learned that the preference for feeding on people was the result of specific genetic changes in them, meaning they evolved to specifically target humans.

They noted that in the areas where the mosquiito samples were taken in sub-Saharan Africa urbanization is happening quickly. This could lead to more mosquito bites in many African cities over the next 30 years. The researchers suggest having people in cities make sure their water supplies are well-managed, clean, and not left open to air to help fight off the growing mosquito threat. (VOA)