Most people think of mosquitos as very annoying creatures, but they are actually much more dangerous than just irritating. Mosquitos are known to spread diseases that kill hundreds of millions of people every year. According to the World Health Organization, close to 725,000 people each year are killed by mosquito-born diseases. Malaria, one of the more well known and dangerous diseases, has affected hundreds of millions of people. Mosquitos are also known to carry other deadly diseases like dengue fever, yellow fever, and encephalitis.