What is Dengue Fever?
The dengue fever virus is carried by Aedes mosquitoes in many tropical countries. These mosquitoes are found most commonly in urban areas and tend to bite during the day-time. An estimated 400 million people are infected with the dengue fever virus each year and around a quarter of these people develop symptoms.
FAQs
In which countries is dengue present?
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Dengue is present in most countries in the tropics. The highest number of reported cases come from Central America, South America and Southeast Asia. Very occasional cases are also reported from temperate regions including Europe and North America.
How many different types of dengue virus are there?
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There are four known serotypes of dengue virus - DEN-1, DEN-2, DEN-3 and DEN-4.
Why is the second dengue infection sometimes worse than the first?
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After most infections, the body develops protective immunity. Antibodies and immune cells are primed by the first infection and can respond rapidly to a subsequent exposure, neutralising the infective agent.
With dengue virus, a protective response against infection with the same dengue serotype develops. But if you are infected by a different serotype, a process called antibody dependent enhancement (ADE) can occur. This is when antibodies for the first dengue serotype attach to the new serotype but fail to neutralise it. Instead, they facilitate uptake of the virus-antibody complex into immune cells where the virus can multiply. This can lead to severe infection.
What to Know
Dengue symptoms
Symptomatic infection usually occurs around four to seven days after the bite of an infected mosquito (with a total range of three to 13 days). Fever, headache, fatigue, eye pain, joint and muscle pain are common, and around half of people develop a rash. Most symptoms resolve in one to two weeks, but some people go on to experience fatigue for several weeks.
In some people, a second dengue infection with a different serotype of dengue virus to their first infection causes severe infection. Leaky blood vessels can develop as can a bleeding tendency. This may cause bruises under the skin, haemorrhage into the gastrointestinal tract and bleeding at other sites. This form of the illness, which can be life-threatening without appropriate therapy, is sometimes referred to as dengue haemorrhagic fever (DHF). In severe cases, the leaking of fluid from blood vessels can result in a drop in blood pressure. This is referred to as dengue shock syndrome (DSS). Both DHF and DSS are rare in people who are travelling to the tropics for the first time.
Dengue diagnosis and treatment
Diagnosis can be made early in the illness by taking blood for PCR testing or detection of a viral protein called NS1. After around four days, antibodies directed against the virus can be detected in blood samples. There is no specific anti-viral medication for dengue virus. Treatment revolves around symptomatic measures, monitoring and treatment of complications when they occur.
Dengue prevention
For most travellers, prevention of dengue fever involves mosquito avoidance. The Aedes mosquito bites during the day and at twilight. Staying indoors during daylight hours reduces the risk. When going outdoors, wearing protective clothing and using effective insect repellant (for example DEET-based) is also advised.
Vaccines are being developed, but these are not yet routinely available in Australia. They must be imported when required. Immunisation is usually reserved for people who have had dengue in the past and will be moving to areas of dengue transmission to live.