DengueDengue is an infection caused by the dengue virus of which there are 4 different subtypes, the disease is transmitted by mosquitoes
Dengue is a viral disease transmitted by mosquitoes which predominantly feed between dawn and dusk.
Symptoms of dengue can include high fever, muscle and joint pains, headache, nausea, vomiting and rash.
Most infections are self-limiting with improvement in symptoms and recovery occurring 3 to 4 days after the onset of the rash.
Severe dengue (also known as dengue haemorrhagic fever) is a more serious form of the disease which is rare in travellers.
The number of reported cases of dengue in UK travellers has been increasing; most cases are acquired in Asia, the Americas and the Caribbean.
There is currently no vaccine available in Europe to prevent dengue. Travellers should avoid mosquito bites.
Dengue is caused by a virus of the genus Flavivirus, within the family Flaviviridae. It is transmitted by the bite of an infected Aedes spp. mosquito which predominantly feed between dawn and dusk.
There are four distinct serotypes of dengue virus (DEN 1, DEN 2, DEN 3 and DEN 4) all of which have the potential to cause either dengue or severe dengue (also known as dengue haemorrhagic fever (DHF)).
During the 18th and 19th centuries, major epidemics occurred at intervals of 10 to 40 years in Asia, Africa, and North America [1, 2]. The Aedes mosquito and the dengue virus were dependent on sailing vessels to transport them from one population to another, and when a new serotype was introduced, new epidemics occurred . The epidemiology of dengue changed after the Second World War, due to increasing economic growth and the urbanisation of South East (SE) Asia in particular, where millions of people moved to the cities. The dengue virus spread rapidly and the disease developed into pandemic proportions .
According to the World Health Organization (WHO), a recent estimate indicates 390 million dengue infections per year (95% credible interval 284–528 million), of which 96 million (67–136 million) present with symptoms .
The disease occurs in Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific .
A study in 2013 estimated that there were up to 3.97 billion people are at risk of infection with dengue viruses in 128 countries . The main vector, Aedes aegypti, is found worldwide between latitudes 35ºN and 35ºS (see figure 1) .
Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas (see figure 1). The Americas, South-East Asia and Western Pacific regions are the most seriously affected .
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Dengue is an emerging disease outside tropical areas, including parts of Europe. During 2010, locally acquired cases were reported in Croatia  and France ; in 2012, an outbreak of dengue in the Autonomous Region of Madeira resulted in over 2000 cases and imported cases have also been detected in ten other countries in Europe [2, 8].
In order to standardise the reporting of dengue, to improve the quality and accuracy of statistics and to detect and monitor incidence and trends of dengue and severe dengue, the WHO has created an online database for sharing current surveillance data (DengueNet) .
Risk for travellers
The chance of contracting dengue is determined by several factors including travel destination, length of exposure in endemic areas, the intensity of dengue transmission and the 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 countries where dengue is endemic are at risk of infection, although determining the actual level of risk is difficult. The true incidence of dengue in travellers is probably underestimated because in many countries, reporting of dengue is not obligatory and, due to its non-specific symptoms, the illness probably under-diagnosed .
Travellers who spend a long period in endemic areas (such as expatriates or aid workers) are at increased risk; however, even short-term visitors may be exposed to the virus [8, 11-13].
Dengue in UK travellers
Dengue does not occur in the United Kingdom; it is a travel-associated infection. The majority of cases that are reported in the UK are acquired in Asia, the Americas and the Caribbean; in 2013, 541 individual cases of dengue were reported in England, Wales and Northern Ireland compared to 343 in 2012 .
Aedes aegypti is the principle vector associated with dengue transmission. A. aegypti are closely associated with human habitation, where they breed in water-filled receptacles (e.g. wells, water-storage containers and used tyres) and rest indoors in cool, dark rooms. In the forest habitat, they breed in water-filled tree holes. They are most active during daylight hours, when they bite from dawn to dusk, but A. aegypti will also feed at night indoors, when lights are on .
Signs and symptoms
In about 75 percent of cases of dengue there are no symptoms . When symptoms occur, the illness begins abruptly after an incubation period of five to eight days. There may be high fever (up to 40oC), often accompanied by a severe headache and retro orbital (behind the eye) pain, myalgia (muscle pain), arthralgia (joint pains), nausea, vomiting, abdominal pain and anorexia. The high temperature can persist for five to six days; around the third to fourth day, a maculopapular skin rash may be seen on the chest, trunk and extremities .
Health professionals should be alert to the importance of looking out for the warning signs of severe disease. Warning signs include mucosal bleeding, abdominal pain, liver enlargement and fluid accumulations.
Severe dengue is characterised by bleeding with major organ functions becoming compromised resulting in bradycardia (slow heart beat), respiratory distress, impaired consciousness, renal failure eventually leading to death if supportive treatment is not available [15, 17, 18].
Diagnosis and treatment
The clinical picture of dengue is often characteristic and the diagnosis is confirmed by blood test (serology and viral detection) [15, 19].
Treatment of dengue and severe dengue is supportive. Most infections are self-limiting with improvement in symptoms and rapid recovery occurring three to four days after the onset of the rash.
Nursing care in hospital with careful management of fever, fluid balance, electrolytes and blood clotting is standard. Intensive care is essential for patients with shock and major organ compromise. With good nursing and medical support, death due to severe dengue is typically less than one percent .
Anti-viral and steroid therapy have not been shown to aid recovery .
Lifelong immunity to the infecting virus serotype occurs in those who recover, however, infection with one serotype does not confer immunity to the other three serotypes or to other flaviviruses.
Health professionals should be alert to the possibility of dengue in those who have recently returned from a dengue risk area presenting with a fever or flu-like illness.
Clinical advice should be sought in the first instance from a local microbiology, virology or infectious disease consultant. Health professionals who suspect a case of dengue should send appropriate samples for testing (with full clinical and travel history) to the Public Health England Rare and Imported Pathogens Laboratory
Prevention is by avoidance of mosquito bites especially during daylight hours. Particular vigilance with bite precautions should be taken around dawn and dusk. Those living in endemic areas should remove rubbish or water containers close to their home where possible; they can be breeding sites for mosquitoes.
There is currently no vaccine available in Europe to prevent dengue in travellers. Several vaccine candidates are in clinical or pre-clinical development [15, 20-21]. One vaccine Dengvaxia® has been licensed in a small number of endemic countries for use in the local population aged between 9 and 45 years of age . The WHO Strategic Advisory Group of Experts (SAGE) reviewed the vaccine in April 2016 and recommended countries consider introduction of the vaccine only in geographic settings (national or subnational) with high endemicity .
WHO recommends prevention of dengue through vector control methods such as mosquito habitat removal and use of insecticides, surveillance, case management and development of future vaccines .
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- European Centres for Disease Prevention and Control. Epidemiological update: Dengue in Madeira, October 2012. [Accessed August 2015]
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