Dengue is a mosquito-borne viral infection that is common in warm, tropical climates. Infection is caused by any one of four closely related dengue viruses (called serotypes) and these can lead to a wide spectrum of symptoms, including some which are extremely mild (unnoticeable) to those that may require medical intervention and hospitalisation. In severe cases, fatalities can occur. There is no treatment for the infection itself but the symptoms that a patient experiences can be managed.

The Aedes aegypti mosquito is considered the primary vector of DENV. It could breed in natural containers such as tree holes and bromeliads, but nowadays it has well adapted to urban habitats and breeds mostly in man-made containers including buckets, mud pots, discarded containers and used tyres, storm water drains etc., thus making dengue an insidious disease in densely populated urban centres. Once a female has laid her eggs, these eggs can remain viable for several months in dry condition, and will hatch when they are in contact with water.

Dengue is a mosquito-borne viral disease that has rapidly spread to all regions of WHO in recent years. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. 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 climate parameters as well as social and environmental factors.

Earlier this year, WHO listed dengue as a potential threat among ten diseases for 2019 and current outbreaks in many countries confirm this observation. Dengue epidemics tend to have seasonal patterns, with transmission often peaking during and after rainy seasons. There are several factors contributing to this increase and they include high mosquito population levels, susceptibility to circulating serotypes, favourable air temperatures, precipitation and humidity, all of which affect the reproduction and feeding patterns of mosquito populations, as well as the dengue virus incubation period. Lack of proactive control interventions and staff are some of the other challenges.

The incidence of dengue has grown dramatically around the world in recent decades. A vast majority of cases are asymptomatic or mild and self-managed, and hence the actual numbers of dengue cases are under-reported. Many cases are also misdiagnosed as other febrile illnesses.Before 1970, only 9 countries had experienced severe dengue epidemics.

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 ~70% of the global burden of disease.

In 2020, dengue affected several countries, with reports of increases in the numbers of cases in Bangladesh, Brazil, Cook Islands, Ecuador, India, Indonesia, Maldives, Mauritania, Mayotte (Fr), Nepal, Singapore, Sri Lanka, Sudan, Thailand, Timor-Leste and Yemen. Dengue continues to affect Brazil, India, Vietnam, the Philippines, Cook Islands, Colombia, Fiji, Kenya, Paraguay, Peru and, Reunion islands.

The COVID-19 pandemic is placing immense pressure on health care and management systems worldwide. WHO has emphasised the importance of sustaining efforts to prevent, detect and treat vector-borne diseases during this pandemic such as dengue and other arboviral diseases, as case numbers increase in several countries and place urban populations at highest risk for both diseases. The combined impact of the COVID-19 and dengue epidemics could have devastating consequences on the populations at risk.