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Disease Information Sheets


Dengue fever is a viral infection transmitted by a daytime biting mosquito. It is found in tropical and sub-tropical regions around the world, predominantly in urban and semi-urban areas. It is a particular risk in South East Asia, South America and the Western Pacific. Most cases of dengue are unpleasant but not fatal. Severe dengue (formerly known as Dengue Haemorrhagic Fever) is a potentially lethal complication that may occur, particularly if the same person is infected repeatedly. Severe dengue is uncommon in travellers, most typically affecting children. About 500,000 people with severe dengue require hospitalisation every year. There are four serotypes (kinds) of dengue virus.

The Dengue Belt and countries at risk of transmission

How common is it?

Some 2.5 billion people – over two fifths of the world's population – are now at risk from dengue. The World Health Organisation (WHO) currently estimates that there may be 50 to 100 million cases of dengue infection worldwide every year. The disease is now endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South East Asia and the Western Pacific.

The incidence of dengue has grown dramatically over recent decades, both through the disease spreading to new areas, but also due to explosive outbreaks. Local transmission of dengue was reported for the first time in France and Croatia in 2010. An outbreak of dengue on Madeira in 2012 resulted in over 1800 cases and imported cases were detected in five other European countries apart from mainland Portugal.

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Are travellers and/or expat workers at risk?

Yes. The risk of dengue depends on the local intensity of transmission and the individual’s exposure to mosquitoes. Both short and long-term visitors are at risk, although there is evidence that long-term visitors are at greater risk than those exposed for shorter periods.


What is the illness?
  • Some people who are infected do not have any symptoms.

  • There is a 5-8 day incubation period between being bitten and becoming ill.

  • If the person has not had dengue before, he/she will experience a fever lasting 1-5 days. The fever may subside and recur after a few days. There may be other flu-like symptoms such as headache, muscle pain and cough.

  • Typically a feint red rash spreads from the trunk to the limbs and face from day 3 to day 5 of the illness.

  • Most cases resolve 3-4 days after the onset of the rash without complications.

  • Severe dengue involves a sudden deterioration in condition between days 2 and 7. There may be bleeding under the skin, from the gums and into the gastrointestinal tract. Shock, respiratory failure and kidney failure may develop.

  • On recovery the individual will be immune for life to the same serotype (kind) of dengue virus, but will still be susceptible to the other three serotypes.


Can it be treated?

There is no specific treatment. Supportive/symptomatic treatment is required.


How can it be prevented?

There is no vaccine. Prevention is by avoiding mosquito bites, particularly at dawn and dusk and during daylight hours. 

  • Spray exposed skin with 30% DEET

  • Treat clothing with insecticide; wear long sleeves and trousers

  • Sleep under an insecticide-treated bed net

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