Written by Dr Adrian Hyzler, Chief Medical Officer and Head of Medical Communications
Updated: August 2019
The World Health Organisation classifies dengue as one of the seventeen ‘Neglected Tropical Diseases’ and it has become a disease of global significance.
Dengue is a severe viral illness that primarily presents with fever. It causes flu-like symptoms, if any at all, but rarely it can have potentially lethal complications. It is endemic throughout the tropics and subtropics and it has become particularly established in urban, poor areas but also affects more affluent neighbourhoods.
It is a leading cause of febrile illness in travellers to Latin America, the Caribbean and Southeast Asia. It is found in over 100 countries throughout the world putting almost half of the world’s population at risk. Dengue has a similar geographic distribution to malaria but presents a greater risk in urban and residential areas than malaria. It is estimated that there are between 100 and 400 million infections annually, a number that has grown dramatically in recent years. This increase is believed to be due to a combination of urbanisation, population growth, increased international travel and global warming. Of the 2.5 billion people living in areas where it is common, 70% are from Asia and the Pacific. There are between 10,000 and 20,000 deaths annually.
It is mainly transmitted through the bite of infected mosquitoes – the same mosquito is responsible for transmission of zika, chikungunya, and yellow fever, as well as other less widely-known viral infections.
KEY FACTS ABOUT DENGUE…
- Dengue is a viral disease transmitted by mosquitoes which predominantly feed between dawn and dusk.
- It is typically found in tropical and subtropical climates but is spreading to temperate regions.
- Symptoms of dengue are flu-like and 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 three to seven days after the onset of the rash.
- Severe dengue is a more serious form of the disease which is rare in travellers.
- Most cases among travellers are acquired in Asia, the Americas and the Caribbean.
- Travellers should check the prevalence of dengue before travelling and take suitable measures to avoid mosquito bites.
TRANSMISSION | How do you get dengue?
Almost all transmission occurs through the bite of the infected female Aedes mosquito, primarily Aedes aegypti and Aedes albopictus. Infection can occur from a solitary bite.
Because the virus remains in the blood of humans for about a week, transmission is also possible through exposure to infected blood, organs, or other tissues (such as bone marrow). In addition, dengue can be transmitted to the new-born baby when the mother is infected near the time of birth. Dengue viruses may also be transmitted through breast milk. There is no evidence of sexual transmission.
Once infected, humans become the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. The virus circulates in the blood of an infected person for 2-7 days, at approximately the same time that the person develops a fever. In parts of Asia and Africa, the transmission cycle may also involve jungle primates that act as a reservoir for the virus.
Dengue infection rates are higher outdoors and around dawn and early evening when these mosquitoes bite most frequently. However, Aedes aegypti breed indoors and are capable of biting anyone throughout the day. The mosquito remains infected for life, usually about 2 to 3 weeks, but is itself not affected by the virus.
Dengue outbreaks have also been attributed to Aedes albopictus and several other species of Aedes mosquitoes. This increases the distribution map of dengue and explains the spread to more temperate climates where these species are better adapted to survive. The Ae. albopictus mosquito is a forest species but has adapted to human environments in the Americas and Europe. The mosquito is often transported long distances aided by the international trade in used tyres in which the eggs are deposited, in collections of rainwater. The eggs can withstand very dry conditions and remain dormant for months while they await favourable conditions for hatching.
SYMPTOMS | What are the symptoms of dengue?
Between half and three quarters of infections cause no symptoms at all. When symptoms do occur they generally present between three and 14 days after the mosquito bite – this is known as the incubation period. The initial symptom is a sudden feverish illness (up to 40°C/ 104°F) that usually lasts for two to seven days.
Other signs and symptoms of uncomplicated dengue infection may include:
- Severe headache
- Eye pain
- Muscle, joint and bone pain
- A red rash on the chest, trunk and hands and feet appear on the third or fourth day
- Minor bleeding in the gums, nose, eyes and blood in urine.
Signs of progression to severe dengue as follows:
- Persistent vomiting
- Severe abdominal pain
- Swelling from fluid retention
- Lethargy and restlessness
- Difficulty breathing.
This typically lasts 24 to 48 hours, and will need hospital treatment, but most people then start to get better. However, a small number may progress to severe bleeding, irreversible shock and death.
Children often experience symptoms similar to those of the common cold and gastroenteritis (vomiting and diarrhoea) and have a greater risk of severe complications.
DIAGNOSIS | How is dengue diagnosed?
A doctor would have a high index of suspicion in anyone who presents with fever and related symptoms in a dengue endemic area. An early blood test can be used to detect the virus. After about four days from the onset of illness, an alternative blood test can detect antibodies in the blood to confirm the diagnosis. There is a cross reaction with other similar viral illnesses, such as yellow fever or Japanese encephalitis, and these may produce false positive results in areas where these infections are also endemic.
It is important to remember that a traveller returning home from an area with endemic dengue may present with fever up to 14 days after their return, since it can take this long for symptoms to develop.
It is always important to tell your doctor about travel abroad when you become sick upon return to your home country.
TREATMENT | How is dengue treated?
There is no specific antiviral treatment for dengue. The most important aspect of management consists of maintaining good hydration, by adequate oral fluids or, if necessary, with intravenous fluids.
Fever should be kept under control with paracetamol / tylenol and tepid sponge baths. Drugs such as aspirin or anti-inflammatories should be avoided since they may exacerbate any bleeding episodes.
Severely ill patients will require admission to an intensive care unit for frequent observation and monitoring. They may require blood products in severe illness. The fatality rate is 1-5%, but less than 1% with adequate treatment.
Sick patients should be kept in a mosquito-free environment in order to reduce the risk of further transmission to others.
PREVENTION | What precautions should I take to prevent getting dengue?
There is a vaccine but it is not available to travellers. Dengvaxia has been licensed in 20 countries but only for use in the local population aged between nine and 45 years of age. It must only be given to people who have been confirmed as having been infected with dengue in the past. The reason for this is that people who have a second infection with a different type of dengue (there are five ‘serotypes’) are at risk of developing the more severe form of the illness. The vaccine consists of three doses and it is thought that it is 60% effective, but more importantly that it prevents more than 80% to 90% of severe cases.
There is no medication that can be taken to prevent dengue.
The risk of infection increases the longer the duration of travel to the dengue region and also where the incidence of dengue is higher, such as during the rainy season or during outbreaks. Consequently, expatriates and aid workers for example, who spend long periods in endemic areas are at increased risk. However, even short-term visitors may be infected by just a solitary bite from an infected mosquito!
In humans recovery from infection by one dengue virus provides lifelong immunity against that particular virus serotype. However, this immunity confers only partial and transient protection against subsequent infection by the other three serotypes of the virus. It is thought that sequential infection increases the risk of developing severe dengue.
The most effective form of prevention is to avoid mosquito bites…
- Screen windows and doors and use air conditioning. The Aedes mosquito typically lives and breeds indoors in dark, cool places.
- Wear clothing that covers arms and legs especially during early morning and late afternoon, when the risk of being bitten is highest – permethrin impregnated clothing affords greater protection.
- Use insect repellent containing DEET 50%, both day and night. DEET sprays are safe to use in pregnancy and when breast feeding, and for children over two months of age.
- Alternative sprays can be used containing picardin or lemon eucalyptus extract.
- Use a knock down spray indoors to clear dwellings of mosquitoes
- For long-term travellers, empty any containers with stagnant water around dwellings in order to minimise mosquito breeding sites.
World Health Organisation – Dengue
Centers for Disease Control and Prevention