Dengue fever is a mosquito-borne viral disease, primarily spread by female Aedes aegypti mosquitoes, that causes symptoms such as sudden high fever, severe headache, joint and muscle pain, and a rash—though most infections are mild or asymptomatic. In about 5% of cases, the illness progresses to severe dengue (formerly dengue hemorrhagic fever), which involves bleeding, plasma leakage, and dangerously low blood pressure, with the risk of this complication heightened by a subsequent infection with a different serotype (a phenomenon known as antibody-dependent enhancement). Prevention relies on mosquito control, and while there is no specific antiviral treatment, two vaccines have been approved: Dengvaxia (2016) for those previously infected and Qdenga (2022) for adults and children over four. First described in 1779, the disease is now endemic in over 100 countries and is expanding into new areas like the Iberian Peninsula and the southern US, partly due to climate change. In 2023 alone, over 5 million infections and 5,000 deaths were reported, though the true numbers are likely much higher due to under-reporting of asymptomatic and mild cases.