magnified many times
Probably dengue fever didn't exist before the late 1700s AD, so in the ancient and medieval worlds there was no dengue fever. Most people think that the virus that causes dengue evolved from some earlier virus that didn't make people sick. Dengue appeared all over the warmer parts of the world at about the same time. Since the late 1700s, the dengue virus has been spreading, and more and more people have been catching dengue fever.
Mosquitoes and how they spread dengue fever
You get dengue fever when a mosquito bites you and the dengue virus travels in the mosquito's spit into your blood. Hardly anyone living in North America or Europe gets dengue fever, but almost half the people in the world live in places where you might get dengue fever. There are about fifty million cases of dengue fever in the world every year. That means about one out of 130 people in the world gets dengue fever every year. There is no vaccination against dengue fever yet, though doctors are trying to invent one. The best way to stop dengue fever is to keep mosquitoes from laying eggs, by not leaving any puddles of water around.
If you catch dengue fever, you suddenly get a rash and a terrible headache and very achy muscles and joints, so that people sometimes call dengue "break-bone fever". There's no real treatment, just taking Tylenol (paracetamol) and drinking lots of water. Most people get better in about a week, though a few people die of it.