Dengue fever (pronounced DEN-geh or "DEN-ghee" ["e" as in pen, silent u, optional "ee" as in "see"]) is a viral tropical disease transmitted by mosquito bites. There is no cure and treatments only manage the symptoms of the disease, some of which can be fatal.
Dengue is a major public health problem in South-East Asia and South Asia, and is also found in Queensland, Australia, the tropical South Pacific islands, Africa, tropical parts of North and South America, including the Caribbean and mainland Central America. Every year over 100 million new cases are reported, about half a million are hospitalized and 25,000 die.
Dengue is not infectious between humans. It is transmitted to humans by the Aedes aegypti mosquito, which is found in tropical regions throughout the world. These mosquitoes carry a flavivirus which causes Dengue fever. Other flaviviruses, also insect-borne, cause Yellow fever, Zika fever, Chikungunya, the West Nile disease, and several types of encephalitis.
The main preventive measures are to prevent the breeding of mosquitoes and to avoid mosquito bites. No vaccine was available until recently, but as of early 2016 the first vaccine is just reaching the market; see below.
Signs and symptoms
About 80% of people infected with the virus have no symptoms at all, or only a mild fever and general malaise. Mild cases without rash may be easily misdiagnosed as flu. Dengue is also easily confused with Zika fever or Chikungunya which are caused by related viruses, carried by the same genus of mosquito, and have similar symptoms.
For the unlucky 20% or so who get full-blown dengue fever, the first symptoms are usually a sudden fever (often over 40°C, 104°F) accompanied by strong head, joint and muscle pains. In the 19th century it was known as "breakbone fever" due to these pains. This is usually soon followed by a bright red rash, often starting on the lower limbs, but it may spread to torso, arms, legs, and face. Nausea, vomiting and abdominal pain are also common. These symptoms usually appear 3-14 days (most commonly 4-7 days) after being bitten by an infected mosquito.
The acute symptoms of the disease typically last 6-7 days, but many patients are miserable for weeks afterward and it can take many months to fully recover. There is no specific treatment, other than fever management. The symptoms can be alleviated with appropriate medication and fatality rates with proper treatment are around 1 in 1000.
A serious complication, fortunately fairly rare, is dengue hemorrhagic fever (DHF), in which blood vessels become more porous and start to leak fluids. The most common symptom is bleeding from the nose, mouth, and gums, but accumulation of fluids in abdomen or lungs, bleeding in the intestinal tract, vaginal bleeding, or bleeding under the skin are also possible. There can be a fever of 42°C (107 °F) or higher, which is an emergency in itself. The fatality rate for DHF with proper treatment is only about 1%, but the treatment involves major interventions — transfusions, other intravenous fluids, often oxygen to compensate for blood or lung problems, ... — and often several days in an intensive care ward.
DHF can lead to dengue shock syndrome (DSS) in which so much fluid is lost that pulse and blood pressure drop precipitously. This is a critical emergency; it is lethal in 90% of cases unless correctly and very promptly treated, and there is some chance of death even with good treatment. A major goal of treatments for DHF is to prevent the patient from progressing to DSS, and this can generally be achieved.
There are four strains of the dengue virus and, for reasons no-one has figured out, DHF seems to occur more often in people who have recovered from an infection with one strain but then get re-infected with a different strain.
In areas with dengue, if you feel ill (especially after being bitten by a mosquito) see a hospital, doctor or health center fast: the presence of dengue can be confirmed with a blood test.
Dengue hemorrhagic fever is a life-threatening illness, and it often kicks in about as the patient is recovering from a bout of dengue fever; if you are recovering but show any DHF symptoms, see a doctor immediately.
Treating DHF properly requires the resources of a modern hospital. If you are out in the countryside and come down with dengue fever, consider evacuating immediately to somewhere with such a hospital so that you can get prompt treatment if it does develop into DHF.
Preventative measures to control and avoid dengue fever focus on avoiding mosquito bites and include:
- Prevention or elimination of standing water sources, such as pools of water that collect in containers, flower pots, discarded tires or coconut shells, etc. Mosquitoes will breed in any standing water in a matter of days. In some countries there are substantial fines for anyone found to have standing water on their property; this is one reason that Singapore is now low-risk for both dengue and malaria.
- Use of mosquito netting especially for the place you sleep in even if mosquitoes "can't enter" the house.
- Use of insect repellent (DEET or picardin are the main agents that have been shown to be most effective) as well as wearing clothing that covers exposed skin.
- Houses constructed in such a way as to reduce the entry of mosquitoes. (e.g. screens on the windows a/c instead of open windows/ventilators...)
Most electronic bug zappers are not effective against mosquitoes since mosquitoes are not attracted to light. There are some models which emit carbon dioxide or octenol (found in the breath of mammals) so they do attract mosquitoes.
As of early 2016, the first vaccine to prevent dengue fever is just reaching the market; it is effective against all four strains of the virus.
Sanofi Pasteur, the French company who developed it, are seeking approval first in countries like Mexico, Thailand, Brazil and the Philippines — places that need it and have moderately high incomes — and leaving US and European approval for later, so travellers may need to get the shot at their destination.