A transmission electron micrograph showing dengue virus virions (the cluster of dark dots near the center)
Source: CDC per University of South Carolina Biomedical Sciences web page (in Spanish)
Dengue — also called "breakbone" fever — is an infectious tropical and subtropical virus from the species Flavivirus and the Flaviviridae family, the same family that produces West Nile virus. Incidences of dengue have risen an alarming 30-fold during the last 50 years, with current estimates showing that 50–100 million people are afflicted annually. It is the most prevalent and rapidly spreading mosquito-borne viral illness in the world.
While the majority of those infected by dengue exhibit no symptoms, others may experience mild symptoms such as fever, headache, and muscle pain. The most severe, life-threatening cases result in dengue hemorrhagic fever, which may cause acute abdominal pain, internal bleeding, and dengue shock syndrome, leading to organ dysfunction.
The virus exists in four distinct serotypes. Exposure to one serotype generally provides a person with long-term immunity to that serotype and short-term immunity to the other three serotypes. Dengue hemorrhagic fever can occur in individuals exposed to one serotype who later become infected with other serotypes. There are no specific antiviral medicines for dengue.