Open Outbreak

Dengue

Also known as: dengue fever, DENV, breakbone fever

Dengue is a viral infection spread mainly by Aedes mosquitoes, especially Aedes aegypti and, to a lesser extent, Aedes albopictus. It is most common in tropical and subtropical places, especially in urban and semi-urban areas. WHO reported that by 2024-04-30, more than 7.6 million dengue cases had been reported worldwide in 2024, including more than 16,000 severe cases and more than 3,000 deaths. Many infections cause no symptoms or only a mild fever, but some people develop severe dengue with shock, heavy bleeding, or organ problems. Symptoms usually begin 3 to 14 days after infection. Dengue has four virus types, and infection with one type does not give lasting protection against the others. This helps explain why outbreaks can return. This session’s sources clearly support mosquito-bite transmission and the global rise in outbreaks. They do not give a clear single source for a standard antiviral treatment or a universal vaccine recommendation, so those points should be treated cautiously here.

Key facts

TransmissionMainly through the bite of infected Aedes mosquitoes, especially Aedes aegypti and, to a lesser extent, Aedes albopictus.
Incubation3 to 14 days after infection.
Case fatalityVaries by outbreak. Examples from WHO notices: 0.47% in Bangladesh in 2023 and 0.25% in Pakistan in 2022. Overall untreated versus treated fatality was not stated in the sources retrieved this session.
Reproduction numberunknown
Vaccineunknown from the sources retrieved in this session
Treatmentunknown from the sources retrieved in this session
Reservoirunknown from the sources retrieved in this session
Endemic regionsTropical and subtropical climates worldwide, mostly in urban and semi-urban areas; major burden reported in the Americas, Southeast Asia, and the Pacific.

Transmission

Dengue spreads to people through the bite of infected mosquitoes, not through casual contact with a sick person. WHO’s recent outbreak notices say the main vector is Aedes aegypti, with Aedes albopictus also able to spread the virus. These mosquitoes are well adapted to towns and cities, which is one reason dengue can spread quickly in crowded urban and semi-urban settings. WHO also notes that dengue has four serotypes, or closely related virus types. Infection with one serotype gives long-term protection only against that same serotype, and only short-term protection against the others. That means a person can get dengue more than once. The sources retrieved here do not provide a settled reproduction number for dengue, so that figure is best left as unknown on this page.

Symptoms and severity

Many dengue infections cause no symptoms, or only a mild febrile illness. When symptoms do appear, they commonly start 3 to 14 days after infection. The encyclopedia source retrieved in this session lists high fever, headache, vomiting, muscle and joint pain, and a rash. Recovery often takes two to seven days. A smaller group of patients develop severe dengue. WHO says severe disease may involve shock, severe bleeding, or severe organ impairment. That is why dengue can be dangerous even though many infections are mild. Case-fatality also varies by place and year. In WHO outbreak reports, Bangladesh reported a case fatality rate of 0.47% in 2023, while Pakistan reported 0.25% in 2022. These outbreak figures should not be read as a single universal fatality rate for every setting.

Treatment and vaccines

The sources gathered for this page do not provide a clear WHO treatment guideline or a clear current global vaccine recommendation, so it is safer to say that specific treatment and vaccine status are unknown from this session’s evidence. What WHO’s 2024 global update does show is that response depends heavily on early detection, surveillance, trained clinical staff, and mosquito control. WHO also reported shortages of good-quality diagnostic kits and shortages of trained clinical and vector-control staff during the current wave of outbreaks. That tells readers something important: health-system capacity matters a lot for outcomes. Because some cases can become severe very quickly, especially when shock or bleeding develops, prompt medical assessment is important for people with warning signs. But this page avoids naming a specific antiviral or vaccine policy because the required source support was not retrieved in this session.

Where it occurs

Dengue is found mainly in tropical and subtropical climates around the world. WHO says it occurs mostly in urban and semi-urban areas. The 2024 global WHO update reported active dengue transmission in 90 countries in 2024, while also warning that the true number is likely higher because some countries have weak detection and reporting systems. Older review literature retrieved here describes the biggest long-running burden in Southeast Asia, the Pacific, and the Americas. Recent WHO notices also show spread or local transmission in places that worry public-health officials because they are new or unusual for dengue. Examples include the first documented locally acquired cases in Iran in 2024 and the first reported dengue outbreak in Chad in 2023. These events do not mean dengue is new globally, but they do show its geographic footprint can expand when vectors are present and conditions allow transmission.

Recent history

On this site, dengue has 48 archived events since 1996, which fits WHO’s picture of a disease that keeps returning in cycles and is now expanding. WHO’s recent notices show a sharp rise. By 2024-04-30, more than 7.6 million cases, more than 16,000 severe cases, and more than 3,000 deaths had been reported to WHO in 2024. In 2023, WHO described a global escalation, with major outbreaks in countries including Bangladesh, Brazil, Burkina Faso, Fiji, Pakistan, the Philippines, and Viet Nam. In the Americas, WHO said close to three million suspected and confirmed cases had already been recorded by 2023-07-01, exceeding the whole of 2022. WHO also flagged important milestones: Chad reported its first dengue outbreak in 2023, and Iran reported its first locally acquired cases in 2024. Together, these reports show both repeated outbreaks and spread into new settings.

What to watch

The main warning signs are not just more cases, but changes that make spread harder to control. WHO highlights several such signals. One is local transmission in new countries or regions, especially where Aedes mosquitoes are already present. Another is an earlier start or longer duration of the dengue season in places where it is already endemic. WHO also points to changes in the distribution or abundance of Aedes aegypti and Aedes albopictus, heavy rainfall, humidity, heat, and large population movements as factors that can increase risk. A shift in circulating serotypes also matters because population immunity may no longer match the viruses in circulation. Finally, WHO warns that strained health systems, shortages of diagnostic kits, and shortages of trained clinical and vector-control staff can make outbreaks more dangerous. This session did not retrieve evidence on antiviral resistance or vaccine supply for dengue, so those remain unknown here.

Related outbreaks

Updated