What Is Dengue Fever?

Dengue fever is a mosquito-borne viral disease caused by dengue virus serotypes 1–4 (DENV 1–4), transmitted primarily by the Aedes aegypti mosquito. It is now endemic in more than 129 countries, placing 3.9 billion people at risk. With approximately 400 million infections annually — 100 million causing clinically apparent disease — dengue is the world's most common arboviral infection. Approximately 40,000 people die from dengue each year. Most infections are mild or asymptomatic, but a dangerous minority progress to severe dengue (dengue hemorrhagic fever or dengue shock syndrome), which can be fatal without hospital care.

Incubation: 4–10 days. Dengue progresses through three phases:

Febrile phase (days 1–3): Sudden high fever (39–40°C), severe headache, retroorbital pain (behind the eyes), intense muscle and joint pain ("breakbone fever"), nausea, vomiting, rash.
Critical phase (days 3–7): Fever subsides but plasma leakage can cause shock. Warning signs: abdominal pain, persistent vomiting, bleeding gums, blood in urine or stool, rapid breathing, sudden drop in temperature. Seek emergency care immediately if these appear.
Recovery phase (day 7+): Fluid reabsorption, gradual improvement. Fatigue may persist for weeks.

Dengue has no specific antiviral. Treatment is supportive. Critical rule: use paracetamol (acetaminophen) only for fever and pain. Never use ibuprofen, aspirin, or other NSAIDs. Dengue causes thrombocytopenia (low platelets) and NSAIDs further inhibit platelet function and irritate the stomach lining, dramatically increasing bleeding risk. IV fluid management is the cornerstone of severe dengue treatment and must be carefully calibrated to prevent both fluid deficit and overload.

Two vaccines are available. Dengvaxia (Sanofi) is approved for ages 9–45 with confirmed prior dengue infection — it worsens disease in dengue-naive individuals. Qdenga (Takeda) is approved for ages 6–16 in multiple countries without pre-screening requirement. Neither is widely available to international travelers. Vector control (eliminating standing water breeding sites) and personal protection (DEET repellent, long clothing) remain the primary prevention tools.

Can you get dengue more than once?: Yes — there are 4 serotypes. Infection with one provides lifelong immunity to that serotype but only short-term cross-protection against others. A second infection with a different serotype carries substantially higher risk of severe dengue due to antibody-dependent enhancement (ADE). Third and fourth infections are typically milder.
How long does dengue fever last?: The acute illness typically lasts 7–10 days. The dangerous critical phase is days 3–7. Fatigue and weakness can persist for 2–4 weeks after fever resolves, even in uncomplicated cases.
Is dengue contagious between people?: No. Dengue is not directly transmissible between people. It requires a mosquito vector — the Aedes aegypti mosquito bites a viremic person, incubates the virus for 8–12 days, then transmits it when biting another person. You cannot catch dengue from being near someone who has it.