Once one person has a virus or parasite that can survive in a mosquito’s body, he or she will give that disease to every single mosquito that bites them, and each of those mosquitoes will give it to every single other person they bite, who will give it to all the mosquitoes they’re bitten by, and so on and so forth.

Most of these diseases arose in tropical climates where mosquitoes are a year-round constant, and those same countries are often less wealthy and less developed, which means more people spending more time exposed to more mosquitoes in the very homelands of mosquito borne illnesses.

It’s still common in many of these places for the average job to be outdoors, working crops or collecting fruit to make a living, often for companies here in the U.S. or Britain. We Westerners basically pay poorer people overseas to put themselves at greater risk in more dangerous environments for a lot of our food.

In some regions it’s rare for people to even have the money for screen or glass in their windows.

The destruction of tropical forest also creates far more environments for mosquitoes, as their larvae can survive in dirtier, more stagnant water than most of their predators can. In a jungle they have fewer options; streams and puddles get colonized by other insects, hungry frogs and many other competitors. Tear down the jungle to make a cow pasture or something, and you make a large area where collected water will get very filthy and attract almost solely mosquitoes. Literally thousands can spawn in just rain-filled bulldozer tracks.

 Some of the deadliest diseases known to man positively thrive off of how our modern civilization operates.