Dengue – Global situation

Global Overview 

Current situation 

The global incidence of dengue has markedly increased over the past two decades, posing a substantial public health challenge. From 2000 to 2019, the World Health Organization (WHO) documented a ten-fold surge in reported cases worldwide increasing from 500 000 to 5.2 million. The year 2019 marked an unprecedented peak, with reported instances spreading across 129 countries.

After a slight decline of cases between the year 2020-2022 due to the COVID-19 pandemic and lower reporting rate, in 2023, an upsurge in dengue cases have been observed globally, characterized by a significant increase in the number, scale, and simultaneous occurrence of multiple outbreaks, spreading into regions previously unaffected by dengue.

Dengue transmission is cyclic and large outbreaks every 3-4 years can be expected. During the COVID-19 pandemic we saw moderate transmission of dengue in some regions and low transmission in others leading to an accumulation of people without immunity to certain dengue virus serotypes. However, the data on the circulating dengue serotypes is limited.

Since the beginning of 2023, ongoing transmission, combined with an unexpected spike in dengue cases have resulted in close to a historic high of over five million cases and more than 5000 dengue-related deaths reported in over 80 countries/territories and five WHO regions: Africa, Americas, South-East Asia, Western Pacific and Eastern Mediterranean Regions globally (Figure 1). Close to 80% of these cases, or 4.1 million, have been reported in the Region of the Americas. Dengue is the most widespread arbovirus and causes the highest number of arboviral disease cases in the Region of the Americas, with cyclic epidemics recurring every 3 to 5 years. In addition, clusters of autochthonous dengue have been reported in the WHO European Region. However, these numbers are likely an underestimate of the true burden as most of the primary infections are asymptomatic and dengue reporting is not mandatory in many countries.

Several factors are associated with the increasing risk of spread of the dengue epidemic including, the changing distribution of the vectors (chiefly Aedes aegypti and Aedes albopictus), especially in previously dengue naïve countries; the consequences of El Nino phenomena in 2023 and climate change leading to increasing temperatures and high rainfall, humidity among others; fragile health systems in the midst of COVID-19 pandemic, political and financial instabilities in countries facing complex humanitarian crises and high population movements. These factors also challenge the response to the epidemic and the risk of further spread to other countries. Weakness in the surveillance systems in many affected countries may have led to delayed reporting and response and missed identification of symptoms, contributing to increased severe dengue outcomes.

WHO has assessed the risk to be high globally considering the increasing risk of transmission and the upsurge of cases and deaths.

Figure 1: Countries/territories/areas reporting autochthonous dengue cases (November 2022- November 2023) *

Between 1 January 2023 and 11 December 2023, a total of 4.1 million suspected dengue cases (cumulative incidence of 419 cases per 100 000 population), including 6710 severe cases (0.16% of suspected cases) and 2049 deaths (CFR 0.05%) were reported from 42 countries and territories in the Region of the Americas, with 15 countries reporting active outbreak. Of the total number of dengue cases until 12 November 2023 (EW 48 of 2023), 1 895 122 (45%) were laboratory confirmed.

Currently, 46 countries and territories systematically report, through the Health Information Platform for the Americas (PLISA), on a weekly basis, the total number of cases, incidence, number of severe cases, number of deaths and lethality due to dengue, as well as entomological surveillance data. As of EW 48, Brazil has reported the highest number of suspected cases in the Region (n = 2 909 404; 1359 cases per 100 000 population), followed by Peru (n= 271 279; 813 cases per 100 000 population), and Mexico (n = 235 616; 179 cases per 100 000 population). In terms of severe dengue, Colombia reported the most cases (1504; 1.35% of cases), followed by Brazil (1474; 0.05% of cases), Mexico (1272; 0.54% of cases), Peru (1065; 0.39% of cases), and Bolivia (640; 0.44% of cases).

Dengue virus (DENV) is transmitted to humans through the bite of infected mosquitoes typically in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. The primary vectors that transmit the disease are Aedes aegypti and, to a lesser extent, Aedes albopictus mosquitoes, though in some regions such as Europe and North America this latter vector is more widespread.

DENV has four serotypes (DENV-1, DENV-2, DENV-3, DENV-4). Infection with one serotype provides long-term immunity to the same serotype and only transient immunity to the other serotypes, after which secondary infections with a different serotype increase the risk for severe dengue. Dengue cases are most commonly asymptomatic or result in mild febrile illness. However, some cases will develop severe dengue, which may involve shock, severe bleeding or severe organ impairment. This stage often starts after the fever has gone away and it is preceded by warning signs such as intense abdominal pain, persistent vomiting, bleeding gums, fluid accumulation, lethargy or restlessness, and liver enlargement.

There is no specific treatment for dengue, but the timely diagnosis of dengue cases, identification of warning signs for severe dengue, and appropriate clinical management are key elements of care to prevent the progression to severe dengue and deaths.

Heterogeneity in capacity across Member States impacts the ability to detect and respond to DENV endemic and epidemic transmission. While the majority of the countries in the Americas, South-East Asian and Western-Pacific regions are endemic for the disease and have the capacity to manage cases, a few countries do not mandate reporting of dengue cases and thus under- or non-reporting of cases results in pockets of vulnerability within regions. Simultaneous outbreaks across multiple WHO regions strain the capacity for epidemic response. The overall capacity to respond to multiple, concurrent outbreaks continues to be strained due to the global lack of resources, including shortages of good quality dengue diagnostic kits for early detection, lack of trained clinical and vector control staff, and lack of resources to support risk community and community engagement interventions. Prevention and control of dengue continue to be variable due to changes in the predominant circulating serotypes and co-circulation of multiple dengue serotypes in the different regions, limited funding, competing health priorities and diverse perceptions about the effectiveness of interventions and control measures. Surveillance and response capacity is particularly limited in many countries in the African region, and as stated earlier, five of the Eastern Mediterranean Member States with DENV are dealing with conflicts and natural disasters.

There is a pressing need to increase advocacy and resource mobilization in an integrated approach to influence policymakers in affected countries within these regions.

The following activities are being undertaken at WHO to support Member States in the response to this event.

Recent data from 2023 emphasize escalated dengue outbreaks in several countries, particularly Bangladesh, Brazil, Burkina Faso, Fiji, Pakistan, the Philippines, and Viet Nam. Additionally, non-endemic countries are increasingly facing dengue as a significant public health concern. The emergence and re-emergence of dengue and its unprecedented worldwide spread are linked to various factors:  i) Changing distribution and adaptation of the Aedes aegypti vector; ii) increased unplanned urbanization and human activities fostering conducive environments for vector-host interaction; iii) Climate change-induced shifts in weather patterns; iv) Fragile healthcare systems amidst political and financial instabilities; v) Co-circulation of multiple dengue serotypes; vi) Challenges in clinical diagnosis due to non-specific symptoms; vii) Inadequate laboratory and testing capacity; viii) Prolonged ongoing concurrent outbreaks, including COVID-19; ix) Lack of specific treatment for dengue; x) Limited behavioral data available on community risk perceptions, awareness and health seeking behaviors: xi) Lack of community centered approach and RCCE resources to support engagement and mobilization of local communities in vector control activities; xi) Insufficient vector surveillance and control capacities and, xii) Lack of coordination among stakeholders, chronic underfunding,  low donor interest and xii) large scale movement of people and goods.

The expansion of DENV beyond its endemic transmission areas presents additional challenges.  A significant population that is immunologically naïve to the current virus circulating, increasing the risk of outbreaks. Moreover, people in these areas might lack awareness of dengue warning signs, leading to potential delays in seeking health care which is critical to reducing mortality from severe disease.  Accessibility challenges to medical facilities, compounded by limited geographical access, heighten the difficulty in accessing basic healthcare services.  These challenges are aggravated by stockouts of essential supplies for prevention and control, laboratory diagnostic reagents, and the need for ongoing training of healthcare workers.

These factors, along with others, including financial crises, mass migration of internally displaced persons (IDPs) and refugees, and longstanding developmental inadequacies, have deprived large populations across all continents of adequate healthcare, consequently increasing their vulnerability to dengue. However, it is important to note that the distribution of dengue risk varies significantly across regions, countries, and within countries.

Based on all the above WHO has assessed the risk at global level as high. Following the risk assessment and an internal grading process, WHO Regional Offices have agreed on priority interventions to implement in support of Member States.

Dengue prevention and outbreak response involves several agencies in the public health sector. Addressing these challenges requires a multidisciplinary and multisectoral integrated approach, especially at national level to achieve its goal of reducing the impact on public health. The strain on epidemic response capacity due to simultaneous concurrent outbreaks coupled with political crises highlights the need for robust emergency response mechanisms and strengthened collaboration among stakeholders. The global lack of resources, including shortages of good quality dengue diagnostic kits for early detection, lack of trained clinical and vector control personnel, and community awareness remain a critical obstacle to an effective response. While coordination efforts with global health organizations like WHO and other partners strive to set common priorities and analyses, the need for continuous support to affected countries and enhanced collaboration is imperative.

Effective vector control measures: 

Effective vector control is key to the prevention and control of the DENV. Vector control activities should target all areas where there is a risk of human-vector contact, such as residences, workplaces, schools, and hospitals. WHO promotes Integrated Vector Management (IVM) to control Aedes species. IVM should include removing potential breeding sites, reducing vector populations, and minimizing individual exposure. This should involve vector control strategies for larvae and adults (i.e., environmental management and source reduction), especially monitoring water storage practices, draining and cleaning household water storage containers weekly, larvicide in non-potable water using WHO-prequalified larvicides at correct dosages, distribution of insecticide-treated nets (ITNs) for fever/dengue inpatients to contain spread of the virus from health facilities. Indoor space spraying for rapidly containing dengue-infected mosquitoes may be challenging to deliver in densely populated areas.

The Global Arbovirus Initiative promotes coordination and collaboration among multisectoral partners, an integrated vector management approach and sustained control measures at all levels. Its guiding principle is to harmonize prevention, surveillance (entomological and epidemiological) and case management with existing health systems, such that they are sustainable, cost-effective and ecologically sound.

Personal Protective Measures:  

Personal protective measures during outdoor activities include topical repellents to exposed skin or the treatment of clothing and using long-sleeved shirts and pants. Additionally, indoor protection can include the use of household insecticide aerosol products, or mosquito coils during the day. Window and door screens can reduce the probability of mosquitoes entering the house. Insecticide-treated nets offer good protection to people against mosquito bites while sleeping during the day. Since Aedes mosquitoes are most active at dawn and dusk, personal protective measures are recommended particularly at these times of day. Personal protection measures and mosquito control should also cover workplaces and schools since the vectors are day-biting mosquitoes.

Entomological Surveillance: 

Entomological surveillance should be undertaken to assess the breeding potential of Aedes mosquitoes in containers and monitor insecticide resistance to help select the most effective insecticide-based interventions.

Case management: 

There is no specific treatment for dengue infection. However, early detection and access to appropriate healthcare for case management can reduce mortality, as can rapid detection of severe dengue cases and timely referrals to tertiary healthcare facilities.

• severe abdominal pain
• persistent vomiting
• rapid breathing
• bleeding gums or nose
• fatigue
• restlessness
• blood in vomit or stool
• being very thirsty
• pale and cold skin
• feeling weak.

People with these severe symptoms should get care right away.

Ministries of Health and partners should closely review local interventions to accept and recommend them for public health programmes for early adaptation to reduce the growing health impact of dengue.

WHO does not recommend that any general travel or trade restrictions be applied to countries/territories/areas based on the available information.

• WHO Fact sheet: Dengue and severe dengue
• Ending the neglect to attain the Sustainable Development Goals: A road map for neglected tropical diseases 2021–2030
• Public Health Situation Analysis: El Niño (October-December 2023)
• Establishing syndromic surveillance and event-based surveillance systems for Zika, dengue and other arboviral diseases;
• Half of world population at risk of dengue virus : WHO
• WHO warns of dengue risk as global warming pushes cases near historic highs
• Laboratory testing for Zika virus and dengue virus infections
• Dengue and severe dengue cases and deaths for the subregions of the Americas
• PAHO dengue situation reports
• PAHO Guidelines for clinical diagnosis and treatment of dengue, chikungunya and zika (2022) 
• Dengue situation in America
• ECDC, increasing risk of mosquito-borne diseases in EU/EEA following spread of Aedes species
• Vector control: the ARS confirms a first indigenous case of dengue in Île-de-France and initiates two mosquito control actions in Limeil-Brévannes (94)
• Dengue cases in Italy: updated data
• WHO Bangladesh. Dengue Situation Report, Issue # 10, 30 Oct 2023
• Disease Outbreak News. Dengue – Bangladesh
• National Dengue Control Unit, Ministry of Health. Publications, 2023
• Western Pacific regional action plan for dengue prevention and control (2016)
• WPRO dengue situation reports

¹DLI (Dengue Like Illness). Case definition: Fever for at least 2 days, in addition to at least two of the following:

i. Nausea or vomiting; ii. Muscle or joint pain; iii. Severe headache or pain behind the eyes; iv. Rash;v. Bleeding