Dengue is a disease primarily of the tropical and subtropical areas, caused by four closely related viruses. It is transmitted by certain day-biting mosquitoes which are closely associated with humans. The most important vectors are Aedes aegypti and Aedes albopictus.

Epidemic dengue has been increasing since the 1980s, with the virus types and vector mosquitoes re-emerging and spreading in the tropics and sub-tropics worldwide. The disease is now found in more than 100 countries throughout the Americas, Africa, the Eastern Mediterranean, South-east Asia, and the western Pacific. The WHO estimates that two fifths of the world's population are now at risk from dengue and that there may be 50 million cases of dengue infection worldwide every year.

An infection may be non-apparent, but can also take the form of a severe, flu-like fever, with rash, vomiting, strong headaches, joint and muscle pains (dengue fever, DF, also called break-bone fever). Additional and potentially fatal complications may include damage of blood vessels with bleeding of the gums, nose, or under the skin (dengue hemorrhagic fever, DHF) and massive bleeding and shock (dengue shock syndrome, DSS).

There is no vaccine and no specific treatment for dengue. The only method of controlling the disease is to combat the vector mosquito.