Am i the only person who didn't have to look up for it? LOL, just kidding - it's because it's a really common disease on tropical and humid countries - since the vector is a mosquito that reproduces itself in places with clean and undisturbed water (like that water that stays on the dish underneath a vase of flowers)
It's like a flu, but a bit more annoying (and the person gets red marks on the body - there's a more severe form, that evolves with hemorrhagic phenomenons, but it isn't very common).