Dengue hemorrhagic fever is the advanced and sometimes potentially life-threatening form of dengue fever; itself a tropical disease caused by the arbovirus DENV and spread by mosquito of the genus aedes (aedes aegypti and aedes albopictus). Mosquitos become infected when biting humans carrying the virus and may then go on to infect others. The main symptoms of dengue hemorrhagic fever include spots of blood appearing on the skin (petechiae) and low blood platelets leading to possible complications including shock.
While there are over 100 million new cases of dengue fever each year, it is only a relatively small proportion that will develop into dengue hemorrhagic fever (around 5%). Risk factors include previous infection by the virus which may have left behind remnant antibodies, or being younger than 12 years old. It is also more common in females and Caucasians.
As long as the symptoms are recognised early, most patients will recover fully from dengue hemorrhagic fever. If it develops into dengue shock syndrome however, then the risk increases significantly and half of untreated patients do not survive. There is no known vaccine or cure for dengue fever, however there are various treatments which can address the symptoms and ultimately improve the outlook.
Dengue fever is also known as 'breakbone fever' (after the joint pain) and comes from the dengue virus. There are actually four closely related serotypes of dengue virus which can lead to the condition (known as DEN-1 through DEN-4). A fifth serotype was discovered recently, though it belongs to the sylvatic cycle meaning it mainly affects non-human primates – for now there have been no sustained epidemics of DEN-5 in human populations (1).
When symptoms are present, they may include fever, joint pain, headaches, muscle soreness and a distinctive rash similar in appearance to measles (the rash occurs in 50-80% of cases that present with symptoms). The symptoms tend to appear after around 4-6 days (though the incubation period can be anywhere from 3 to 14 days) and last for up to 10 days. These symptoms are often biphasic in nature, meaning that they may disappear and then return again in short cycles of one or two days.
Though it is spread by mosquitos, dengue fever is not otherwise contagious. In around 80% of cases dengue virus is asymptomatic or will only present very mild symptoms. The condition itself is not life-threatening unless it develops into dengue hemorrhagic fever.
Symptoms and Characteristics of Dengue Hemorrhagic Fever
In around 5% of cases the condition will progress into dengue hemorrhagic fever. Symptoms of dengue hemorrhagic fever can include bleeding, low levels of blood platelets and leakage of blood plasma. This can in some cases ultimately lead to dengue shock syndrome where blood pressure falls dangerously low. The mortality rate of dengue fever is around 1-5% without medical attention and 1% with treatment (2).
Bleeding will appear as small spots of blood on the skin called 'petechiae', with larger patches beneath the surface. The affected patient might first notice feelings of restlessness, perspiration, low appetite, headache, blood shot eyes and malaise. In severe cases they may also experience bleeding from the nose and gums. Plasma leakage can result in fluid accumulation in the chest and abdominal cavity and can lead to a lowered blood supply to the organs and possible resulting damage.
In some cases dengue hemorrhagic fever will lead to shock which is the most dangerous point. While in shock, patients will break into a cold sweat with a low body temperature and clammy extremities. In some cases shock may lead to death. In other cases shock will be followed by a one day crisis period after which the patient will begin to recover. Other potential complications include encephalopathy, brain damage, seizure and liver damage.
Diagnosis and Treatment
If you are in an area where dengue fever is known to occur and you notice any symptoms of the condition then you should seek immediate medical attention for diagnosis and treatment. Diagnosis can involve analysis of liver enzymes, arterial blood gases, electrolytes, haematocrit, blood tests (looking for traces of the virus in the blood), platelet count and tourniquet tests (looking for petechiae beneath the tourniquet). An X-ray may be used to demonstrate pleural effusion.
There is no available cure for dengue fever so treatment of dengue hemorrhagic fever instead focuses on addressing symptoms. This may include:
Prevention and Control
The disease is endemic to over 110 countries and at-risk areas cover nearly half of the world's population (3). It is particularly common in the Americas, South-East Asia and the Western Pacific. The number of reported cases is currently on the rise however as the virus spreads to new areas.
When travelling to these areas, it is crucial to take measures to avoid infection. Practical prevention simply involves avoiding mosquito bites. Recommended strategies include the use of thick clothing, mosquito repellent (containing DEET) and nets. It is also helpful to avoid travelling during the times of day when mosquitos are most active.
There is no vaccine against dengue fever, however previous infection by the specific serotype of the virus will provide subsequent lifelong immunity against that specific serotype. Infection by each serotype also provides temporary immunity against other types (cross-immunity), though after this period infection by other forms of the virus will come with increased likelihood of developing into dengue hemorrhagic fever (due to remaining antibodies).
Numerous ongoing initiatives are attempting to abate the presence of mosquitos. These include the use of guppy to prey on mosquito larvae as well as attempts to infect mosquitos with wolbachia bacteria to provide them with resistance to the virus. Research is also being conducted into the development of vaccines, though there is concern that a vaccine might increase the risk of severe forms of the disease as is already the case with lingering antibodies from different serotypes. Antiviral drugs are a possible alternative which are being developed to treat dengue fever and hopefully prevent it from developing into dengue hemorrhagic fever (4).
For now, the best advice is to avoid exposure to mosquitos in at-risk areas and to seek immediate medical attention if you notice any symptoms.