Dengue Fever

In the past, the disease was widespread in tropical and subtropical countries. In the meantime, it also occurs sporadically in other areas because of climate change. There were isolated cases in France, Spain and Italy in 2023.

Nevertheless, dengue fever is a classic motion sickness. In the case of travel returnees, one must always think of dengue fever if they have corresponding symptoms.

Dengue fever has spread rapidly in recent decades. In the last 50 years, the number of infected people has increased thirtyfold. Experts estimate that between 284 and 528 million people worldwide contract dengue fever every year.

Vaccination for Dengue Fever

Vaccination against dengue fever is worth considering if you are planning to travel to an endemic area. There are currently two vaccines on the market to protect against dengue fever: Dengvaxia and Qdenga. However, these vaccines are not intended to be used unrestrictedly.

Dengue fever: transmission and incubation period

The dengue virus is transmitted by a bite of the Aedes mosquito – most commonly by the yellow fever or tiger mosquito (Aedes aegypti or Stegomyia aegytpi), sometimes also by the Asian tiger mosquito (Aedes or Stegomyia albopictus).

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 on to humans.

The incubation period of dengue fever is two to 14 days. During this period, the person is already infected with the virus, but has not yet developed symptoms.

Can humans infect each other with dengue?

Usually, people become infected with dengue viruses through the bite of Aedes mosquitoes. The mosquitoes can also pick up the infected blood of sick people and transmit it to other people.

Dengue Fever: Symptoms

The symptoms of dengue fever are often very non-specific and resemble an ordinary flu: Typically, those affected have a high fever (over 40 degrees Celsius in severe cases), chills, headaches, joint and limb pain.

Because of the severe muscle pain, dengue fever is also called “bone crusher fever“. The fever is often biphasic. Along with the second bout of fever, a rubella-like, itchy rash may appear all over the body.

Other possible accompanying symptoms of dengue fever are, for example, fatigue, nausea, vomiting and swollen lymph nodes. Some patients also report a bitter or metallic taste in the mouth (dysgeusia).

Complication 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 that can also be life-threatening. They occur mainly in children and adolescents under 15 years of age, as well as in patients who have already had dengue disease:

Severe dengue fever (obsolete: dengue haemorrhagic fever – DHF): In severe dengue fever, an acute fever outbreak is followed by symptoms caused by a sharp drop in blood platelets (thrombocytopenia).

Various bleeding occurs, such as pinhead-sized bleeding in the skin or mucous membranes (petechiae), bleeding of the nose and gums, and gastrointestinal bleeding (with vomiting of blood and bloody stools).

Dengue shock syndrome (DSS): When blood pressure derails due to the condition, the heart can no longer pump enough blood throughout the body. As a result, the heart rate rises sharply. Nevertheless, vital organs such as the brain and kidneys are no longer adequately supplied.

Warning signs of such complications include:

• Sudden abdominal pain
• Repeated vomiting
• Sudden drop in body temperature below 36°C
• Sudden bleeding, especially of the mucous membranes
• Confusion, restlessness, light headedness, or other disturbances in consciousness
• Shock symptoms, such as a sudden drop in blood pressure or a rapid pulse

Both complications are potentially life-threatening and require hospital treatment. The tricky thing is that they usually only occur when the patient already feels better, often between the third and seventh day of the disease.

In most cases, those affected have not had a fever for 24 to 48 hours at this point. Therefore, they often assume that the disease will regress.

For this reason, it is also referred to as the so-called critical phase, since at this point in time the course of the disease becomes apparent and a medical decision must be made as to whether (drastic) countermeasures are necessary.

Dengue Fever: course of the disease and prognosis

As a rule, dengue fever progresses without complications. Most patients recover within a few days. However, the fatigue can last for a few more weeks.

There is an increased risk of complications of dengue fever in those affected who suffer from a lack of fluid intake, are younger than 15 years of age or do not receive medical treatment. A second infection with dengue viruses is also dangerous:

After a dengue fever infection, you are immune to the respective type of dengue virus for life. However, you can become infected with one of the other three types of virus and become ill again.

This second infection is then often more severe (for example in the form of haemorrhagic dengue fever). Experts suspect that an overreaction of the immune system is responsible for the more severe course of the disease.

People who have already contracted dengue fever must therefore be particularly careful when travelling to the tropics again.

Risk of death

Especially in the case of severe dengue fever (formerly: DHF) and dengue shock syndrome (DSS), timely intensive medical treatment is very important.

The mortality rate (lethality) of severe dengue fever is up to 20 percent. DSS is even more dangerous: without appropriate treatment, up to 50 percent of patients die from this form of dengue fever.

With timely therapy, on the other hand, mortality drops to one percent or less.

Dengue fever: treatment

There is no causal (causal) therapy for this infection. You can only alleviate the symptoms, but not fight the virus itself.

Dengue fever treatment does not differ significantly from the treatment of flu in the fever phase without complications: it is important to drink enough fluids. In addition, you can take a pain-relieving and fever-reducing medication such as paracetamol for the high fever and pain.

If there are no complications, outpatient treatment is sufficient. Nevertheless, those affected should go to the doctor regularly and have their course of the disease monitored. In this way, warning signs can be detected at an early stage. If the described signs occur, the patient should be admitted to hospital as an inpatient.

In the hospital, vital signs (heart rate, respiratory rate, blood pressure, etc.) can be reliably monitored. In addition, infusions or blood reserves can be administered if necessary.

Dengue fever in pregnancy and lactation

The consequences of dengue fever on pregnancy have not yet been clearly scientifically clarified. Researchers have observed that severe courses of pregnancy occur again and again. This affects both the expectant mother and the fetus.

There are also isolated reports of pregnant women who have passed the virus on to their unborn child through blood. In medicine, this transmission path is referred to as “vertical transmission”.

Infection of a developing child is often associated with the risk of malformations. Whether malformations occur and what type they are depends on the stage of pregnancy at the time of infection. Individual circumstances also play a role.

It is not possible to predict the exact course of an infection with dengue fever during pregnancy.

However, studies conclude that increased mortality of the mother, the fetus or later the newborn can be associated with a dengue infection. So, infection during pregnancy is dangerous.

The dengue virus can pass into breast milk during breastfeeding. Therefore, even though these cases have rarely been described, it is possible for an infected mother to infect her newborn while breastfeeding. Infants are usually more severely affected by dengue fever. In some cases, they develop inflammation of the brain (encephalitis).

Dengue fever: prevention

In principle, infection with the dengue virus can be prevented by vaccination and appropriate measures (exposure prophylaxis).

For more information on vaccination against dengue fever, please refer to the accompanying text.

In order to reduce the risk of dengue infection, travellers should focus above all on reliable exposure prophylaxis. So, you should protect yourself from mosquito bites when traveling to risk areas. To do this, experts recommend the following protective measures:

• Wear long pants and tops with 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 (mesh/inch2) – over sleeping places
• Install fly screens on windows and doors (impregnated with insecticides)

Dengue fever: Examinations and Diagnosis

A specialist doctor, such as a tropical doctor or a travel doctor, can often suspect an infection with the dengue virus based on the symptoms described and the information that the person concerned has been in a risk country.

The doctor obtains this information, including on trips that have taken place, during the initial consultation with the patient (anamnesis).

The physical examination is also important. It includes:

• 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

The suspicion of dengue fever can be confirmed by blood tests: a blood sample is examined for corresponding antigens and specific antibodies (serology). A PCR test can detect the virus in the patient’s blood.

If those affected do not come to the doctor until a few days after the onset of symptoms, the viruses may no longer be detectable. They only stay in the body for a short time. Therefore, a negative PCR test cannot rule out dengue fever.

In addition, the examination looks for signs of a tendency to bleed, for example in the form of bleeding gums, nosebleeds or small skin bleedings (petechiae). To check the increased tendency to bleed, the so-called tourniquet test is also performed:

For this purpose, a blood pressure cuff is placed on the patient’s upper arm and inflated to a value between the systolic and diastolic blood pressure. After about ten minutes, the cuff is removed and it is checked whether small bleedings (petechiae) have formed on the forearm.

However, the tourniquet test is not a reliable diagnostic criterion for dengue fever. A positive test result can also occur with other diseases.

A Recent Update in the UAE

With the heavy rainfall across the Emirates last week, healthcare facilities across the UAE are grappling with an increase in waterborne illnesses following unprecedented rainfall, which has inundated several neighbourhoods, especially across some of the northern Emirates. Common cases reported include dengue fever, respiratory infections, and skin infections attributed to prolonged exposure to water and damp environments.

The average number of hospitals visits due to the latest floods have increased to 40 no’s up from the usual 25 no’s. Local experts state that they expect more mosquito-borne illnesses and skin conditions in the next few weeks because of water accumulation during the rains. MOHAP has proactively released preventive and health awareness tips for residents of UAE to ensure their health and safety in the next coming weeks.