The chance of contracting dengue is determined by several factors, including destination, length of exposure, intensity of transmission and season of travel. Risk is thought to be higher during periods of intense mosquito feeding activity (two to three hours after dawn and during the early evening).
All travellers to dengue endemic countries are at risk, although determining actual risk level is difficult. True dengue incidence in travellers is probably underestimated as in many countries dengue reporting is not obligatory. Also, due to non-specific symptoms, dengue is probably under-diagnosed.
Travellers who spend long periods in endemic areas (such as expatriates or aid workers) are at increased risk. However, even short-term visitors may be exposed.
Overview
Dengue (break-bone fever) is a viral infection that spreads from mosquitoes to people. It is more common in tropical and subtropical climates.
In severe cases, dengue can be fatal.
Symptoms
If symptoms occur, they usually begin 4–10 days after infection and last for 2–7 days. Symptoms may include:
- • high fever (40°C/104°F)
- • severe headache
- • pain behind the eyes
- • muscle and joint pains
- • nausea
- • vomiting
- • swollen glands
- • rash
Individuals who are infected for the second time are at greater risk of severe dengue.
Severe dengue symptoms often come after the fever has gone away:
- • 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 seek urgent medical attention.
Global Burden
The incidence of dengue has grown dramatically around the world in recent decades, with cases reported to WHO increased from 505 430 cases in 2000 to 5.2 million in 2019. 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.
One modelling estimate indicates 390 million dengue virus infections per year of which 96 million manifests clinically. Another study on the prevalence of dengue estimates that 3.9 billion people are at risk of infection with dengue viruses.
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 including Europe, and explosive outbreaks are occurring. Local transmission was reported for the first time in France and Croatia in 2010 and imported cases were detected in 3 other European countries.
The largest number of dengue cases ever reported globally was in 2019. All regions were affected, and dengue transmission was recorded in Afghanistan for the first time. The American Region reported 3.1 million cases, with more than 25 000 classified as severe. A high number of cases were reported in Bangladesh, Malaysia, Philippines, Vietnam, in Asia.
Dengue continues to affect Brazil, Colombia, the Cook Islands, Fiji, India, Kenya, Paraguay, Peru, the Philippines, the Reunion Islands and Vietnam as of 2021.
Transmission
The virus is transmitted to humans through the bites of infected female mosquitoes, primarily the Aedes aegypti mosquito. Other species within the Aedes genus can also act as vectors, but their contribution is secondary to Aedes aegypti.
After feeding on a DENV-infected person, the virus replicates in the mosquito midgut before disseminating to secondary tissues, including the salivary glands. The time it takes from ingesting the virus to actual transmission to a new host is termed the extrinsic incubation period (EIP). The EIP takes about 8–12 days when the ambient temperature is between 25–28°C. Variations in the extrinsic incubation period are not only influenced by ambient temperature; several factors such as the magnitude of daily temperature fluctuations, virus genotype, and initial viral concentration can also alter the time it takes for a mosquito to transmit the virus. Once infectious, the mosquito can transmit the virus for the rest of its life.
Vaccine
As of January 2023, a new vaccine Qdenga® has been licensed in the UK for the prevention of dengue disease in individuals from 4 years of age.
The vaccine is given in 2 doses, 3 months apart from each other. In return, they offer lifetime immunity to the disease.
The UK Joint Committee on Vaccination and Immunisation (JCVI) and WHO Strategic Advisory Group of Experts (SAGE) are in the process of reviewing the product information. Recommendations on the use of this vaccine will be published in due course.