How does dengue fever affect platelet counts?

Dengue fever

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 no symptoms, otherwise typically flu-like symptoms (such as fever, chills, headache and body aches, muscle pain); in case of complications Blood clotting disorders, vomiting, drop in blood pressure, restlessness, drowsiness
  • Treatment: symptomatic with hydration and pain relievers and febrile drugs; in-patient intensive care in the event of complications
  • Forecast: mostly benign course; increased risk of complications in children and secondary infections
  • Prevention: Avoiding mosquito bites (long clothes, mosquito net, mosquito repellent, etc.)

Dengue fever: routes of infection and occurrence

Dengue fever is caused by the dengue virus, which comes in four different variants (serotypes): DENV 1-4. All of them are from the Aedes mosquito transmitted - most often 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 areas or generally in human-populated areas. 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. It is also the female mosquitoes that pass the disease on to humans.

Can people infect each other with dengue?

Usually people become infected with dengue viruses through a bite from Aedes mosquitoes. The stinging animals can also absorb the infected blood of sick people and transmit it to other people.

A direct dengue transmission from person to person - i.e. without the presence of Aedes mosquitoes - does not usually take place.

In contrast to flu viruses, for example, dengue viruses do not occur in saliva according to current knowledge. Dengue fever cannot be transmitted through sneezing, coughing or kissing. However, there are isolated cases in which researchers assume that individuals find out about unprotected sex have infected.

The European Center for Disease Prevention and Control (ECDC) therefore advises that patients with or suspected of having dengue fever should not practice or practice safer sex during the period of illness. However, the experts also emphasize that further studies are necessary for a more precise statement.

So far, researchers have been able to detect dengue virus RNA in semen, vaginal secretions and urine. To what extent an infection can occur through this remains unclear (it is also conceivable that an infection via small injuries that occurred during sexual intercourse and infected blood is transferred is also conceivable). A positive test does not necessarily mean that the person affected is contagious, as it only detects the genetic make-up of the dengue virus.

There are also isolated reports on Pregnant womenwho passed the virus on to their unborn child through the blood. Doctors call this transmission path vertical transmission. A transmission of the virus through breast milk has so far been assumed in a single case. In addition, the dengue virus can be infected through infected blood (transfusions, needlestick injuries).

Although very rarely reported, the direct transmission of the dengue virus between people does not play a relevant role in the spread of dengue fever, according to experts. The transmission via Aedes mosquitoes is decisive.

Occurrence of dengue fever

Dengue fever is the most common and fastest spreading mosquito-borne infectious disease worldwide. Southeast Asia, South and Central America, parts of the Pacific such as New Caledonia and Hawaii as well as Africa and Australia are particularly affected.

Due to global warming, the Asian tiger mosquito is meanwhile also widespread in southern Europe and is expanding its settlement area. In recent years, there have been isolated local dengue infections in Europe, such as in Madeira, Croatia, France or Spain. Experts fear that the mosquito will also increasingly spread to continental Europe.

The Aedes mosquito is not at home in Germany so far. German dengue fever patients were infected in tropical and subtropical countries. Since Germans like to travel more and more, the number of dengue fever cases introduced has risen sharply in recent years. Around 600 cases were reported in Germany in 2018.

According to reporting data from the Infection Protection Act (IfSG), the most common countries of infection in 2018 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 is one of the notifiable diseases in Germany. This means that the attending physician must report every case to the health department. This measure should help to identify larger outbreaks as quickly as possible and to be able to take countermeasures.

Dengue fever: diseases are on the rise

Dengue fever has spread over the past few decades. Over the past 50 years, the number of people infected has increased thirty-fold. Experts estimate that between 284 and 528 million people worldwide contract the dengue virus every year.

Insidious tropical diseases

  • Ebola - deadly viruses

    The Ebola virus is one of the most dangerous pathogens in the world. It belongs to the group of hemorrhagic fevers - febrile diseases that are accompanied by internal bleeding. The virus spreads to the whole organism and destroys the blood vessels. Bleeding in the gastrointestinal tract, spleen and lungs is usually fatal.
  • Rapid infection

    There are repeated epidemics in Africa, as here in Zaire in 1995. Most infected people die within a few days. The Ebola virus is transmitted from person to person through direct physical contact, as well as when one comes into contact with body excretions from infected people. Since there are no drugs that fight the virus directly, only symptoms can be treated.
  • Malaria from mosquito bite

    Malaria is caused by single-cell blood parasites called plasmodia. They are transmitted through bites of the anopheles mosquito. The disease is usually characterized by regular attacks of fever. The most dangerous forms are fatal in many cases.
  • Insecticides against the spread of malaria

    This historical picture from 1961 shows two men spraying the insecticide DDT in an Indian village. However, since DDT accumulates in adipose tissue and is suspected of causing cancer, its use is now banned in many countries or only permitted to a very limited extent.
  • Leishmaniasis

    Leishmaniasis is caused by single-cell parasites, so-called leishmanias, which are transmitted by mosquitoes. Some species just stick to the skin. Then, as shown here, the so-called oriental bump (cutaneous leishmaniasis) occurs. However, other leishmanias affect important organs of the body and cause kala-azar (visceral leishmaniasis). Extreme enlargement, especially of the spleen, is possible, which is why many patients develop a large abdominal circumference. Without treatment, this disease is fatal in 80 to 90 percent.
  • leprosy

    Leprosy - Leprosy is caused by the bacterium Mycobacterium leprae, a relative of the tuberculosis pathogen. The infection probably takes place via contaminated nasal secretions or via the resulting, weeping skin ulcers. However, leprosy is far less contagious than is usually assumed.
  • Marburg fever

    Together with Ebola, Marburg fever is one of the most serious infectious diseases in humans. Patients suffer from fever with disorientation and impaired consciousness up to coma. The mortality rate with Marburg fever is between 30 and 90 percent. The incubation period is only four to seven days. There is a risk of infection for the entire duration of the illness. Even corpses can still be infectious.
  • Elephantiasis

    Lymphatic filariasis is caused by roundworms. Transferred by mosquito bites, the larvae migrate into the lymphatic system where they trigger inflammation. The permanent lymph congestion causes the affected parts of the body to swell. This massive enlargement of arms, legs, testicles or breasts is called elephant disease (elephantiasis).
  • Zika

    The Zika virus (here in red in the picture) was actually considered a harmless pathogen for a long time. Because normally infected people get a maximum of a little fever and a rash. However, it has been known since 2015 that the fetuses of pregnant women who become infected can develop malformations of the brain. And: It is spreading more and more, especially in South America at the moment.
  • Yellow fever

    The yellow fever virus is transmitted through mosquito bites. In severe cases, bleeding from the skin and mucous membranes occurs. In some cases there are also neurological and psychological symptoms, meningitis, kidney and liver failure.
  • Sleeping sickness

    The pathogens causing sleeping sickness (trypanosomes) are transmitted to humans through the bite of the tsetse fly. Sleeping sickness itself develops several months to years after the infection. The patients suffer from concentration disorders, personality changes (noticeable irritability) and disorders in the sleep-wake rhythm. In addition, they can no longer take in food and lose weight. Usually an increasing need for sleep develops, in addition to which there are often paralysis, cramps or muscle tremors. The disease is almost always fatal.
  • Chagas

    Chagas disease is caused by unicellular parasites (trypanosomes). They are transmitted through the bite of bedbugs. The pathogen causes fever, abdominal pain and diarrhea. The kidneys and liver also enlarge. If the disease does not heal, it can develop serious long-term effects that can even lead to heart failure.
  • Dysentery

    Bacterial dysentery is triggered by rod-shaped bacteria, the Shigella. The group A specimens found in the tropics form a poison that can severely damage the intestinal mucosa. Violent, slimy-bloody diarrhea are the result. If the poison gets into the bloodstream, it can cause circulatory shock and various nerve disorders. This severe form is fatal in up to ten percent of cases.
  • River blindness

    River blindness is caused by the nematode Onchocerca volvulus. The larvae (microfilariae) are transmitted to humans by blood-sucking black flies. The adult worms encapsulate themselves under the skin, but can also migrate into the eye, where they lead to blindness.
  • Dengue

    Dengue fever is a viral infection that is transmitted by mosquitoes such as the female Aedes aegypti shown here. The symptoms are usually similar to those of severe flu. In rare cases, internal bleeding can occur, which can be fatal.
  • Schistosomiasis

    The pathogens of schistosomiasis are pair leeches (schistosomes) - a genus one to two centimeters long. When bathing in contaminated water, the worm larvae penetrate the body through the skin and initially cause severe itching. If left untreated, the leeches implant themselves in various organs, for example in the liver.
  • Schistosomiasis infestation of the liver

    If the parasite attacks the liver, as in the case of the boy pictured here, it can lead to considerable water retention in the abdomen.
  • Lassa fever

    The photo shows the treatment of a woman suffering from Lassa fever in Sierra Leone. The virus is transmitted by certain African rats and causes severe flu-like symptoms. Among other things, edema (water retention) forms in the eyelids and face. In severe cases, bleeding of the internal organs, skin and mucous membranes eventually occurs, which can be fatal.
  • West Nile fever

    West Nile fever is a viral infection that is transmitted by mosquitoes. It does not cause any symptoms in most infected people. Around 20 percent suffer from flu-like symptoms such as fever, headache, chills, nausea or vomiting. However, complications such as encephalitis or meningitis can occur.

Dengue fever: symptoms

The time between the bite of the Aedes mosquito and the appearance of the first symptoms (incubation period) is three to 14 days. Most of the time, the infection breaks out between the 4th and 7th day.

The symptoms of dengue fever are often very unspecific and are similar to those of ordinary flu: Typically, the patient has high fever (up to 40 degrees Celsius), chills, Head-, Joint and limb pain. Because of the severe muscle pain, dengue fever is also "Bone Breaker Fever". The fever often has two peaks (biphasic). Together with the second fever, a rubella-like, itchy rash occur all over the body. Other possible accompanying symptoms in dengue fever are, for example Exhaustion, nausea,Vomit as swollen lymph nodes.

Many infected people also show no symptoms at all (especially children).

Complications in dengue fever

In the majority of patients, dengue fever heals without any further consequences. In some cases, however, there are complications: Doctors differentiate between two serious disease courses that can also be life-threatening. They occur mainly in children and adolescents under the age of 15 and generally in patients who have already suffered from dengue:

Dengue Hemorrhagic Fever (DHF): In hemorrhagic dengue fever, an acute outbreak of fever is followed by symptoms that are caused by a sharp drop in blood platelets (thrombocytopenia) - there is various bleeding such as pinhead-sized bleeding into the skin or mucous membranes (petechiae), nose and gum bleeding as well as gastrointestinal bleeding ( vomiting blood and bloody stools).

Dengue Shock Syndrome (DSS): If the blood pressure derails due to the illness, the heart can no longer pump enough blood around 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 are:

  • sudden abdominal pain
  • repeated vomiting
  • sudden drop in body temperature below 36 ° C
  • sudden bleeding
  • Confusion, agitation, or lightheadedness
  • sudden drop in blood pressure
  • fast pulse

Both complications are potentially life threatening and require hospital treatment. The tricky thing: They usually only appear when the patient is already feeling better again, often between the third and seventh day of the illness. For this reason, one speaks of the in this context critical phase, because now the course of the disease is revealed and the doctor has to decide whether (drastic) countermeasures need to be taken.

Dengue fever: treatment

There is no causal therapy for this infection. This means that the doctor can only alleviate the symptoms, but not fight the virus itself.

Dengue fever treatment does not differ significantly in the fever phase without complications from that of the flu: One is important adequate hydration. You can also take action against the high fever and pain pain reliever and antipyretic drug like taking acetaminophen. Pain relievers and fever medicines, which impair blood clotting and thus increase the bleeding tendency, are not suitable. These include above all acetylsalicylic acid (ASA), but also ibuprofen.

As long as there are no complications, the patient does not necessarily have to go to the hospital. However, as soon as signs of bleeding appear or a shock threatens, inpatient treatment (possibly in the intensive care unit) is unavoidable. The vital parameters (heart and breathing rate, blood pressure, etc.) can be precisely monitored there. In addition, the patients are given infusions or blood reserves as needed.

The risk of complications is particularly high when the fever subsides. Any deterioration in health should then be reported to the doctor immediately.

Dengue fever: prevention

In October 2018, the European Medicines Agency (EMA) approved a vaccine against dengue for the European market. For most EU citizens, however, this authorization does not matter. It is restricted to people who are nine to 45 years old, who live in an endemic area (e.g. La Réunion, Guadeloupe or French Polynesia) and have ever suffered from dengue fever. The dengue vaccine is also not permitted as a travel vaccine.

Research has shown that people who have not had dengue fever and have been vaccinated have a slightly increased risk of developing serious dengue. That is why only people who have survived the infection receive the dengue vaccination.

According to the Robert Koch Institute, scientists are researching several other vaccines against dengue fever, some of them in clinical test phases. Until then, some measures will help to prevent dengue fever in the first place. The most important thing is to protect yourself from mosquito bites when traveling to risk countries (Exposure prophylaxis). The following protective measures are recommended:

  • wear long trousers and long sleeves
  • Apply repellents (mosquito sprays) to skin and clothing
  • Mosquito nets with a mesh size of no more than 1.2 mm - this corresponds to approx. 200 MESH (meshes / inch2) - stretch over the bed
  • Install fly screens on windows and doors (impregnated with insecticides)