Dengue is an acute febrile disease caused by infection with a group B arbovirus of four serotypes, transmitted by the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. Endemic throughout the tropics and subtropics, uncomplicated dengue is rarely fatal, although return to normal health after an attack may take several weeks. It does not always have a benign course, however, and can be complicated by hemorrhagic manifestations (hemorrhagic dengue) and circulatory collapse (dengue shock syndrome) with a potentially fatal outcome unless facilities are available for the urgent medical treatment of those affected.

Typical uncomplicated dengue has an incubation period of 3 to 15 days and is characterized by abrupt onset of chills, headache, lumbar backache, and severe prostration. Body temperature rises rapidly, perhaps reaching as high as 40°C; bradycardia (slow heart rate) and hypotension (low blood pressure) accompany the high fever. Conjunctival injection, lymph node enlargement, and a pale, pink rash, especially noticeable on the face, are usually present during this first phase of the disease. In classical dengue, the fever lasts for 48 to 96 hours initially, subsides for 24 hours or so, and then returns (saddleback fever), although the peak of temperature is usually lower in the second phase than in the first. A characteristic red rash appears in the second phase, usually covering the trunk and extremities, but sparing the face. The fever, rash, and headache, together with the other pains, are known as the dengue triad. The acute illness ends in 8 to 10 days, and one attack confers immunity to the particular dengue subtype.