Brief overview
- What is dengue fever? A viral infection transmitted by the Aedes mosquito.
- Occurrence: mainly in tropical and subtropical countries, but also (occasionally) in Europe.
- Symptoms: sometimes none, otherwise typically flu-like symptoms (such as fever, chills, headache, aching limbs, muscle aches); in case of complications, among others, blood clotting disorders, vomiting, drop in blood pressure, restlessness, drowsiness.
- Prognosis: usually benign course; increased risk of complications in children and second infections
- Prevention: Avoid mosquito bites (long clothing, mosquito net, mosquito repellent, etc.), vaccination if necessary.
Dengue fever: infection routes and incidence
These mosquitoes are mainly found in urban environments or generally in regions populated by humans. They prefer to lay their eggs near water (bottles, rain barrels, buckets, etc.). If females are infected, they can transmit the virus directly to the brood. The female mosquitoes are also the ones that pass the disease to humans.
Can people infect each other with dengue?
Direct dengue transmission from person to person – i.e. without the presence of Aedes mosquitoes – does not usually occur.
Unlike flu viruses, for example, dengue viruses are not found in saliva, according to current knowledge. So dengue fever cannot be transmitted by sneezing, coughing or kissing. However, there are individual cases in which researchers assume that people have become infected through unprotected sexual intercourse.
Researchers have been able to detect dengue virus RNA in semen, vaginal secretions and urine. However, it remains unclear to what extent this can lead to infection (it is also conceivable that infection can occur via small injuries sustained during sexual intercourse, and thus infected blood is transmitted). A positive test does not necessarily mean that the affected person is infectious, as this only detects the genetic material of the dengue virus.
Although very rarely reported, direct transmission of dengue virus among humans does not play a relevant role in the spread of dengue fever according to experts. The decisive factor is transmission via Aedes mosquitoes.
Occurrence of dengue fever
Due to global warming, however, the Asian tiger mosquito is now also widespread in southern Europe and continues to expand its area of settlement. In recent years, there have already been isolated cases of dengue infection in Europe, for example in Madeira, Croatia, France and Spain. Experts fear that the mosquito will also increasingly spread to continental Europe.
The most common countries of infection in 2018, according to Infection Protection Act (IfSG) reporting data, were:
- Thailand: 38 percent
- India: 8 percent
- Maldives: 5 percent
- Indonesia: 5 percent
- Cuba: 4 percent
- Cambodia: 4 percent
- Sri Lanka: 4 percent
- Vietnam: 3 percent
- Mexico: 2 percent
- Tanzania: 2 percent
- Others: 25 percent
Dengue fever: illnesses on the rise
Dengue fever has spread rapidly in recent decades. In the last 50 years, the number of infected people has increased thirty-fold. Experts estimate that between 284 and 528 million people worldwide contract dengue virus each year.
Dengue fever: symptoms
Many infected persons also show no symptoms at all (especially children).
Complications of dengue fever
In the majority of patients, dengue fever heals without further consequences. In some cases, however, there are complications: Doctors distinguish between two serious courses of the disease, which can also become life-threatening. They occur mainly in children and adolescents under 15 years of age, and generally in patients who have already had dengue:
Dengue Shock Syndrome (DSS): When blood pressure is derailed due to the disease, the heart can no longer pump enough blood through the body. As a result, the heart rate increases sharply. Nevertheless, vital organs such as the brain and kidneys are no longer adequately supplied.
Warning signs of such complications are:
- sudden abdominal pain
- repeated vomiting
- sudden drop in body temperature to below 36° C
- sudden bleeding
- sudden drop in blood pressure
- rapid pulse
Dengue fever: treatment
There is no causal therapy for this infection. This means that the doctor can only relieve the symptoms, but not fight the virus itself.
As long as no complications occur, the patient does not necessarily need to be hospitalized. However, as soon as signs of bleeding appear or shock is imminent, inpatient treatment (possibly in the intensive care unit) is unavoidable. There, vital signs (heart rate, respiratory rate, blood pressure, etc.) can be closely monitored. In addition, infusions or blood units are administered to patients as needed.
Dengue fever: prevention
In principle, dengue fever can be prevented by vaccination and by exposure prophylaxis.
Dengue vaccination
The first dengue vaccine was licensed in the EU in December 2018. Medical professionals administer three doses of the vaccine at six-month intervals.
The second dengue vaccine received its approval in the EU in December 2022. It is administered in a two-dose regimen with a three-month interval between the first and second vaccine doses.
Approved for children four years of age and older, adolescents and adults. Currently (June 2023), the relevant agencies are considering a possible vaccination recommendation for travelers to dengue endemic areas.
Exposure prophylaxis
- Wear long pants and long sleeves
- Apply repellents (mosquito sprays) to skin and clothing
- Stretch mosquito nets with a mesh size of no more than 1.2 mm – equivalent to about 200 MESH (meshes/inch2) – over the bed
- Put fly screens on windows and doors (impregnated with insecticides)
Dengue fever: examinations and diagnosis.
In the initial phase, the main symptoms of dengue fever are indistinguishable from those of a normal flu. An appropriately specialized physician such as a tropical doctor can nevertheless often already suspect an infection with “dengue fever” on the basis of the symptoms described and the information that the affected person has been in a risk country. The physician obtains such information during the initial consultation with the patient (anamnesis).
- Temperature, pulse and blood pressure measurement
- Listening to heart and lung sounds
- Palpation of the superficial lymph nodes
- Examination of the throat and mucous membranes
Suspicion of dengue fever can be confirmed by blood tests: A blood sample from the patient is tested for dengue virus and specific antibodies to the pathogen. Rapid tests to detect specific antibodies are also available.
Dengue fever: course of the disease and prognosis
As a rule, dengue fever runs its course without complications. Most patients recover within a few days. However, fatigue may persist for several weeks.
There is an increased risk of complications from dengue fever in patients who do not drink enough or are younger than 15 years of age. A second infection with dengue viruses is also dangerous:
Mortality risk
Especially in dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), timely intensive medical treatment is very important. Mortality (lethality) in DHF ranges from six to 30 percent. DSS is even more dangerous: without adequate treatment, 40 to 50 percent of patients die from this severe form of dengue fever. With timely treatment, however, mortality drops to one percent or less.
