Dengue fever

Dengue fever is a viral disease transmitted by mosquitoes of the genus Aedes.

Dengue is widespread in tropical and subtropical regions of Asia, Latin America and Africa. Dengue fever is therefore classified as a tropical disease.

However, there have also been some isolated cases in non-tropical regions, such as southern Europe.

According to estimates, approximately 400 million people worldwide contract dengue virus every year. People traveling to at-risk regions are at risk of contracting the virus.

For this reason, it is important to be well informed before traveling and to take all necessary protective measures.

Dengue fever can be severe, mild or occur without any symptoms at all. It normally takes between 4 and 10 days following infection for symptoms to begin (this is known as the incubation period).

Uncomplicated dengue fever

In most people, an infection with the virus causes flu-like symptoms or no symptoms at all. Symptoms, when they occur, include fever, chills and severe headaches and bone and limb pain. Nausea, vomiting and a skin rash similar to that seen in measles may also occur.

For most patients, the symptoms subside after 2 to 7 days. However, it can take weeks until they feel completely healthy again.

Severe dengue fever

Some people experience a severe form of the disease. The severe form primarily affects children, young adults and people who were previously infected with another subtype of the dengue virus.

The severe form is known as hemorrhagic dengue fever. Hemorrhagic means that hemorrhages (severe bleeding) occur. This begins around 5 days after the fever has subsided.

Restlessness, anxiety, cold sweats and heart palpitations are also experienced. Blood vessels become more permeable, there is a drop in the number of platelets (thrombocytes) in the blood and blood clotting is impaired.

As a result, blood pressure drops. There is limited blood supply to the lungs, liver, kidneys and intestinal tract and, later, to the heart and brain. Eventually, the infected person experiences cardiovascular failure. This is known as dengue shock syndrome.

If left untreated, severe dengue fever is usually fatal. However, 99 percent of patients with the severe form of the disease survive if they receive intensive care treatment.

Dengue fever is primarily transmitted to humans by Aedes mosquitoes that are active during the day. The main carrier of the virus is the Egyptian tiger mosquito (Aedes aegypti).

The virus can also be transmitted in the opposite direction, i.e., from humans to mosquitoes. This is why the virus is more often spread between people living in the same household – an infected member of the household may be bitten by a mosquito, which then becomes infected with the virus. The same mosquito may then bite other members of the household, and the virus is spread.

In rare cases, pregnant women can transmit the dengue virus to their unborn child. Transmission via blood or organ donation is also possible, but is a rare occurrence.

Virus subtypes

A distinction is made between four different subtypes (serotypes) of the dengue virus (DENV-1 to DENV-4). People who recover from an infection with one subtype have life-long immunity against this subtype. It is assumed that they also acquire immunity against the other subtypes, although this immunity only lasts one to two years.

As there are four different subtypes of the virus, it is possible to become infected by dengue fever four times. The risk of becoming more severely ill from dengue fever is slightly increased when contracting it for a second time.

It is thought that the antibodies created by the body after the first instance of the disease can intensify the symptoms of a new infection by a different dengue subtype.

At present, there is no risk of becoming infected with the dengue virus in Germany. Dengue generally only occurs in tropical and subtropical countries.

The risk to travelers of becoming sick with dengue fever depends on multiple factors. They include:

• the travel destination
• the duration of the trip
• the season
• measures taken to repel mosquitoes
• the current situation as regards dengue fever in the travel destination
• a previous infection with the dengue virus

When traveling abroad, it’s best to find out in advance about the situation regarding dengue virus in the destination region. Protective measures can then be taken to prevent a dengue infection.

For up-to-date information about the various infectious diseases occurring in foreign countries, see the website of the German Federal Foreign Office (Auswärtiges Amt).

Just under 4 billion people live in regions at risk for the spread of dengue fever. A total of almost 130 countries are currently classified as at-risk regions. Most of these are Asian countries, followed by countries in Central and South America.

Dengue fever worldwide

According to estimates, approximately 400 million people worldwide contract dengue virus every year. Only one quarter of people who contract the virus become ill with dengue fever. The other three quarters experience an infection without symptoms.

Observations made over extended periods of time indicate a sharp rise in the number of dengue fever infections – the frequency of dengue infections is now eight times greater than it was 20 years ago. The number of deaths quadrupled between the years 2000 and 2015.

Possible causes discussed are the increase in population density in metropolitan areas, modern modes of transport leading to increasing mobility and climate change.

Dengue fever in Germany

Every year, between 600 and 800 cases of dengue fever are reported in Germany in people returning from travel abroad. Most of these are people returning from South and Southeast Asia, as well as South and Central America. To date, barely any cases of severe dengue have been recorded in Germany.

Protection against mosquitoes also offers protection against dengue fever. Various protective measures can be used, which work best in combination.

Protecting the body

The most important measure travelers can take is consistent protection of the entire body from mosquitoes. The World Health Organization (WHO) recommends mosquito repellent for the skin that contains the active substances DEET (diethyltoluamide), IR3535 or icaridin.

Wearing light-colored clothing with long sleeves made of thick material is also recommended. Clothing should also be coated with insect repellent. This type of protection is very important during daylight hours in particular, as dengue-transmitting mosquitoes are diurnal (active during the day). However, these mosquitoes may also be active around artificial lighting in the evening or at night.

Protecting accommodation

Air conditioning, insect protection on windows and mosquito nets over beds help protect living and sleeping quarters against dengue fever and other diseases spread by mosquitoes.

The Foreign Office has published a leaflet on preventing exposure, which details effective measures for preventing insect bites.

Vaccination

Various vaccines against the dengue virus have been approved by the European Medicines Agency (EMA).

Anyone traveling to a dengue risk area should consult a doctor in advance to determine whether vaccination is advisable.

If a person becomes ill while traveling or after returning home and suspects an infection with dengue fever, it is important to inform a doctor when and where the trip took place.

For diagnosis in the early stages of the disease, doctors first take a blood sample and send it to a laboratory for analysis. PCR analysis can detect the genetic material of the dengue virus in the sample. Alternatively, a rapid test can be used to detect the virus in the blood sample immediately in the doctor’s office.

A blood sample can also be sent to the lab if an infection is only suspected at a later stage of the illness or in a person who previously recovered from another dengue infection. After about a week following infection, antibodies produced by the body against the dengue virus can be detected in a laboratory analysis.

There is no treatment for the dengue virus itself. Only the symptoms are treated. Outpatient treatment is usually possible.

The most important treatment measures are:

• bed rest
• drinking plenty of fluids
• pain-relieving and fever-reducing medication, such as paracetamol

Treatment in hospital is advised if the following circumstances apply:

• insufficient fluid intake or diminished urination
• a decline in overall health, restlessness or apathy
• a low blood platelet (thrombocyte) count
• hemorrhages (bleeding)