Dengue

Dengue is caused by dengue viruses, commonly grouped into four serotypes, DENV-1 through DENV-4. The European Centre for Disease Prevention and Control reports that a fifth isolate was identified in Malaysia in 2013, but says its epidemiological significance remains unclear. The main route of transmission is the bite of an infected mosquito of the genus Aedes, particularly Aedes aegypti and Aedes albopictus. In urban outbreaks, transmission typically follows a human–mosquito–human cycle: a mosquito acquires the virus while feeding on an infected person and can later pass it to another person. Dengue is not spread by ordinary casual contact. Rare transmission through infected blood or from a pregnant person to an infant around birth has also been documented.

Many dengue infections are asymptomatic or cause only mild illness. When symptoms occur, they commonly include fever, headache, pain behind the eyes, muscle or joint pain, nausea, vomiting and rash. The World Health Organization reports that symptoms usually begin four to ten days after infection and last two to seven days. These symptoms are not unique to dengue, so clinical assessment and laboratory testing may be used to distinguish it from other febrile illnesses.

A small proportion of infections progress to severe dengue, which may involve plasma leakage, shock, severe bleeding or impairment of organs. Warning signs can appear as fever subsides, so severe illness is not defined simply by how high the fever is. Infection with one serotype provides long-term immunity to that serotype but only short-lived protection against the others. A second dengue infection carries a higher risk of severe disease, although severe dengue can also occur during a first or later infection.

Dengue occurs mainly in tropical and subtropical regions and is common in urban and semi-urban settings where competent mosquito vectors are present. The World Health Organization estimates that about half of the world's population is at risk and that 100–400 million infections occur annually. Estimates vary because many infections are not clinically apparent and surveillance differs. International travel can carry the virus between regions, while local transmission depends on the presence of suitable mosquito populations and environmental conditions.

Public-health prevention focuses on controlling Aedes mosquitoes and reducing opportunities for them to breed and bite, alongside surveillance and community communication. The specific mix of measures depends on local mosquito ecology and health systems. There is no specific antiviral medicine for dengue; treatment is supportive, with early recognition and access to appropriate medical care especially important in severe cases. Vaccines are available in some settings, but recommendations and eligibility depend on the product and national policy, so vaccination is not a universal substitute for vector control.