Dengue

Unique identifier / Notation

BI0207

Synonyms

Break Bone Fever

Dengue is a mosquito-borne disease that is caused by a virus of the Flaviviridae family and transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, A. albopictus. The incidence of dengue has grown dramatically around the world in recent decades, with cases reported to WHO increasing from 505 430 cases in 2000 to 5.2 million in 2019 (adapted from WHO, 2024).

Primary reference(s)

WHO, 2024. Dengue and severe dengue. World Health Organization (WHO). Accessed 29 May 2025

Annotations

Additional scientific description

Dengue is a mosquito-borne viral disease that is transmitted by female mosquitoes mainly of the species Aedes aegypti.  Other species within the Aedes genus can also act as vectors, but their contribution is normally secondary to Aedes aegypti. However, in 2023, a surge in local transmission of dengue by Aedes albopictus (tiger mosquito) has been seen in Europe (WHO, 2024a).

These mosquitoes are also vectors of chikungunya, yellow fever and Zika viruses. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature, relative humidity and unplanned rapid urbanisation (WHO, 2024a).

Dengue poses an increasingly large public health threat, with an estimated 3.8 billion people (95% confidence interval [CI]: 3.5 billion-4.1 billion) living in areas at risk of the disease, most of which are in Asia, Africa, and the Americas in 2015. Urbanization with increasing population densities, population movement, and climate change have led to the geographical expansion of the Aedes vector species and thus contributed to the increase in dengue incidence. There are an estimated 100-400 million infections each year (WHO, 2024b).

The disease is now endemic in more than 100 countries in the WHO Regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The Americas, South-East Asia and Western Pacific regions are the most seriously affected, with Asia representing around 70% of the global disease burden. Dengue is spreading to new areas in Europe, the Eastern Mediterranean and South America (WHO, 2024a).

Dengue is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death. Symptoms usually last for 2-7 days, after an incubation period of 4-10 days after the bite from an infected mosquito (WHO, 2024a).

Dengue causes a wide spectrum of diseases, ranging from subclinical disease (people may not know they are even infected) to severe flu-like symptoms in those infected. Although less common, some people develop severe dengue, which can be any number of complications associated with severe bleeding, organ impairment and/or plasma leakage. Severe dengue has a higher risk of death when not managed appropriately. (WHO, 2024a).

Mosquitoes can become infected by people who are viremic with the dengue virus. This can be someone who has a symptomatic dengue infection, someone who is yet to have a symptomatic infection (they are pre-symptomatic), and also someone who shows no signs of illness (they are asymptomatic). Human-to-mosquito transmission can occur up to 2 days before someone shows symptoms of the illness, and up to 2 days after the fever has resolved.

The risk of mosquito infection is positively associated with high viremia and high fever in the patient; conversely, high levels of DENV-specific antibodies are associated with a decreased risk of mosquito infection. Most people are viremic for about 4-5 days, but viremia can last as long as 12 days. Following infection with one DENV serotype, antibodies that are serotype-specific (homotypic) and cross-reactive with other serotypes (heterotypic) are induced. Following a primary infection with one DENV serotype, long-lasting homotypic protection is elicited. Cross-reactive heterotypic protection, however, is short-term and declines rapidly within a matter of 2 years. As heterotypic protection wanes, there is a risk of severe dengue following a second infection with another serotype.

There is no specific antiviral treatment for dengue, so measures to prevent severe disease and death rely primarily on supportive management with volume replacement. Patients with severe dengue often require in-hospital management in intensive care settings to mitigate poor clinical outcomes that may be caused by vascular leakage or severe bleeding.

The WHO recommends three methods of dengue surveillance: epidemiological surveillance, vector surveillance and monitoring behavioural impact (WHO, no date).

Metrics and numeric limits

Since the beginning of 2023 ongoing transmission, combined with an unexpected spike in dengue cases, resulted in a historic high of over 6.5 million cases and more than 7300 dengue-related deaths reported. The WHO Region of the Americas reported 4.5 million cases, with 2300 deaths. A high number of cases were reported in Asia: Bangladesh (321 000), Malaysia (111 400), Thailand (150 000), and Vietnam (369 000) (WHO, 2024a).

Key relevant UN convention / multilateral treaty

International Health Regulations (2005), 3rd ed. (WHO, 2016).

Drivers

The primary mode of transmission of the dengue virus between humans involves mosquito vectors. There is evidence, however, of the possibility of maternal transmission (from a pregnant mother to her baby). At the same time, vertical transmission rates appear low, with the risk of vertical transmission seemingly linked to the timing of the dengue infection during the pregnancy. When a mother does have a dengue infection when she is pregnant, babies may suffer from pre-term birth, low birthweight, and foetal distress (WHO, 2024a).

Rare cases of transmission via blood products, organ donation and transfusions have been recorded. Similarly, transovarial transmission of the virus within mosquitoes has also been recorded. Previous infection with DENV increases the risk of the individual developing severe dengue (WHO, 2024a).

Impacts

The highest number of dengue cases was recorded in 2023, affecting over 80 countries in all regions of WHO. Since the beginning of 2023, ongoing transmission, combined with an unexpected spike in dengue cases. Several factors are associated with the increasing risk of spread of the dengue epidemic: the changing distribution of the vectors (chiefly Aedes aegypti and Aedes albopictus mosquitoes), especially in previously dengue naïve countries; the consequences of El Niño phenomena in 2023 and climate change leading to increasing temperatures and high rainfall and humidity; fragile health systems in the midst of the COVID-19 pandemic; and political and financial instabilities in countries facing complex humanitarian crises and high population movements (WHO, 2024a).

Community risks to dengue also depend on a population’s knowledge, attitude and practice towards dengue, as the exposure is closely related to behaviours such as water storage, plant keeping, and self-protection against mosquito bites.  Routine vector surveillance and control activities engaging communities greatly enhance a community’s resilience (WHO, 2024a).

Multi-hazard context

Urbanization with increasing population densities, population movement, and climate change have led to the geographical expansion of the Aedes vector species and thus contributed to the increase in dengue incidence. Vectors might adapt to new environments and climate. The interaction between the dengue virus, the host and the environment is dynamic. Consequently, disease risks may change and shift with climate change in tropical and subtropical areas, in combination with increased urbanization and movement of populations (WHO, 2024a).

Risk Management

The mosquitoes that spread dengue are active during the day. Lower the risk of getting dengue by protecting from mosquito bites by using clothes that cover as much as possible; mosquito nets if sleeping during the day, ideally nets sprayed with insect repellent; window screens; mosquito repellents (containing DEET, Picaridin or IR3535); and coils and vaporizers (WHO, 2024a).

Mosquito breeding can be prevented by preventing mosquitoes from accessing egg-laying habitats through environmental management and modification; disposing of solid waste properly and removing artificial man-made habitats that can hold water; covering, emptying and cleaning domestic water storage containers weekly; and applying appropriate insecticides to outdoor water storage containers (WHO, 2024a).

There are currently 2 licensed dengue vaccines: CYD-TDV (Dengvaxia, Sanofi); and TAK-003 (Qdenga, Takeda). Both are tetravalent live-attenuated vaccines but differ in the extent of chimerization and the genome backbone, as well as in efficacy and safety. Vaccination against dengue should be viewed as part of an integrated strategy to control the disease, including vector control, proper case management, community education, and community engagement (WHO, 2024b).

Dengue prevention and control depends on effective vector control measures. Sustained community involvement can improve vector control efforts substantially. There is an ongoing need to adhere to other disease preventive measures such as well- executed and sustained vector control using the WHO Integrated Vector Management (IVM) approach, which is a rational decision-making process for the optimal use of resources for vector control (WHO Western Pacific, 2019). Recently some countries have successfully lowered the incidence of arboviral infections such as dengue through vector control with Wolbachia infection of mosquitoes that decreases their ability to transmit arboviruses.

The WHO responds to dengue in the following ways: supports countries in the confirmation of outbreaks through its collaborating network of laboratories; provides technical support and guidance to countries for the effective management of dengue outbreaks; supports countries to improve their reporting systems and capture the true burden of the disease; provides training on clinical management, diagnosis and vector control at the country and regional level with some of its collaborating centres; formulates evidence-based strategies and policies; supports countries in the development of dengue prevention and control strategies and adopting the Global Vector Control Response (2017–2030); reviews the development of new tools, including insecticide products and application technologies; gathers official records of dengue and severe dengue from over 100 Member States; and publishes guidelines and handbooks for surveillance, case management, diagnosis, dengue prevention and control for Member States (WHO, 2024a).

Monitoring

WHO supports countries to conduct all-hazards strategic risk assessment in the contexts of health emergencies and disasters, which results in the development of a country's risk profile. Empowered with the country risk profile, inclusive of a seasonal risk calendar, countries can anticipate potential emergencies before they occur to trigger early alerts and inform early actions (WHO, 2021).

WHO's Early Warning, Alert and Response System (EWARS) has been designed to improve disease outbreak detection in emergency settings, such as in countries in conflict or following a disaster from natural hazards. It is a simple and cost-effective way to rapidly set up a disease surveillance system. EWARS is deployed during an emergency as an adjunct to the national disease surveillance system. WHO works with Ministries of Health and health sector partners to train local health workers to use the system. After the emergency, EWARS should re-integrate back into the national system (WHO, 2023).