Dengue fever is a mosquito-borne disease caused by dengue virus, prevalent in tropical and subtropical areas. Mild cases happen frequently; asymptomatic infections are uncommon. Symptoms typically begin 3 to 14 days after infection. They may include a high fever, headache, vomiting, muscle and joint pains, and a characteristic skin itching and skin rash. Recovery generally takes two to seven days. In a small proportion of cases, the disease develops into severe dengue (previously known as dengue hemorrhagic fever or dengue shock syndrome) with bleeding, low levels of blood platelets, blood plasma leakage, and dangerously low blood pressure.

Dengue virus has four confirmed serotypes; infection with one type usually gives lifelong immunity to that type, but only short-term immunity to the others. Subsequent infection with a different type increases the risk of severe complications, so-called Antibody-Dependent Enhancement (ADE). The symptoms of dengue resemble many other diseases including malaria, influenza, and Zika. Blood tests are available to confirm the diagnosis including detecting viral RNA, or antibodies to the virus.