The dengue fever (also known as “tropical flu”) is a viral disease caused by an arbovirus which comes in 4 serotypes: DEN-1, DEN-2, DEN-3 and DEN-4. It is transmitted to humans via the bite of a mosquito infected by the virus. Extremely rare, the virus can also be transmitted through a blood transfusion or organ transplant.
The dengue or tropical flu virus, which is rife mainly in the intertropical zone, belongs to the flavivirus family, such as the Zika virus, yellow fever, West Nile, etc. They are arboviruses (short for arthropod-borne viruses), because they have the particularity of being transmitted by arthropods, blood-sucking insects such as mosquitoes.
There are four different types (or serotypes) of dengue virus, with specific immunity for each subtype, but no cross-immunity between the 4 subtypes. This means that you cannot be infected a second time with a virus of the same serotype, but that it is possible to contract dengue fever from one of the other three types.
According to a hypothesis supported by the WHO, a second infection with another serotype is ten times more likely to develop a severe form than with a first infection, but this theory is currently disputed by many experts.
Dengue is the most common human arbovirus with 50 to 100 million cases per year worldwide. Its incidence has multiplied by 30 in fifty years. The dengue virus has long remained confined to Southeast Asia, before spreading to the Indian Ocean, the Pacific, South America, Central America, the Caribbean, but continues to expand due to anarchic urban development, the increase in international trade and climate change.
Causes of dengue fever
The main vector of the dengue virus is the Aedes aegypti mosquito which lives in urban areas and breeds mainly in containers with standing water. It is the female who stings, mainly during the day, with a peak of activity early in the morning and in the evening before dusk.
A second potential vector of dengue fever is the diurnal Aedes albopictus (or “tiger mosquito” which also transmits chikungunya), which occurs in Asia and has spread to North America and Europe. With great ease of adaptation in temperate zones, infections have been increasing even in colder climate.
The mode of contamination is classic: the mosquito becomes infected by biting an already infected person and can thus transmit the virus by biting another individual. Once in the body, the virus multiplies and persists for 3 to 10 days. The person infected with dengue is not contagious to another human being. But they can infect other mosquitoes of the genus Aedes if they are bitten again within a period of 1 to 2 days before the onset of symptoms and up to 7 days later.
Symptoms of the dengue fever
Dengue fever manifests as a “tropical” flu, with at the beginning:
- a high fever of sudden onset,
- muscle and joint pain,
Two or three days later:
- the fever drops before rising
- a very characteristic rash, similar to measles, appears in one in two cases of one,
- some bleeding of the skin and / or mucous membranes (cutaneomucosal bleeding) appears. This bleeding can present as spontaneous bruises (bruises on the skin), petechiae (small red dots on the surface of the skin), nosebleeds, bleeding gums, vomiting blood or blood in the skin. stool.
The evolution of dengue fever
Most often it evolves towards regression and healing in 4 to 5 days, leaving some fatigue. Dengue fever affects people of all ages. The disease starts within 3 to 14 days after the mosquito bite, with a 4 to 7-day on average.
Dengue fever is in the vast majority of cases benign
- it can even go unnoticed in 50 to 90% of cases
- but often crippling by pain and fever. The major risk is that of severe dengue fever, with hemorrhagic complications or a state of shock.
Imported dengue fever is relatively common in the United States. It is necessary to consult a doctor if a fever or flu-like illness occurs a few days after returning from a trip to a tropical zone, which can correspond to dengue, but also to chikungunya or malaria.
In all cases, the doctor will look for signs of potential severity, bleeding from the skin or mucous membranes, drop in blood pressure, and thrombocytopenia (decrease in the number of platelets on the blood count).
Early diagnosis can be made by testing for the NS1 antigen, a dengue virus protein detected in the serum of people with dengue fever upon onset of fever; the identification of the virus can also be done early.
The search for IgM-type antibodies is only positive around the 6th or 7th day of fever and persists on average for 2 to 3 months. Other more sophisticated biological examinations, such as PCR or viral cultures, are reserved for research or very specialized laboratories in reference centers.
The biological diagnosis allows the declaration of the disease; on the other hand, if we accept the theory that a second infection could be more severe, it is better for a person to know whether or not they have already had a dengue episode, in order to adopt even more preventive measures.
Severe dengue fever is a life-threatening complication with the onset of shock or bleeding complications. Usually after the resurgence of fever, the infection returns and can progress in rare cases (1% of cases in people with symptoms of dengue) to severe dengue. Clinical vigilance should be maximal around the 4th day.
In the hemorrhagic form, blood accumulates in the skin vessels, the rash becomes hemorrhagic and petechiae (small skin spots of red to purplish color, related to the infiltration of blood under the skin), bruises are observed (hematomas), sometimes accompanied by mucous or internal bleeding, digestive or cerebral in particular.
The unfavorable evolution can also be towards a state of shock: the fluids of the body leave the vessels, going to accumulate in various organs, causing edemas, effusions of the pleura, of the pericardium (membrane around the heart), or peritoneum (membrane in the abdomen) and a drop in blood pressure. This leads to a risk of circulatory failure, a drop in body temperature.
In endemic areas, these serious forms mainly concern children; in case of imported dengue, they can occur at any age and in any individual, but will be even more severe in the most vulnerable people. The management of these severe forms is done in the intensive care unit in order to compensate for the various failures. Thus, the mortality of these severe dengues is very low in countries where health structures are developed, but can reach 10% in countries without adequate resuscitation structures.
There is no specific treatment for dengue fever. The treatment is symptomatic, intended to fight against pain and fever. Non-steroidal anti-inflammatory drugs and especially aspirin are contraindicated due to thrombocytopenia (low number of platelets) and the risk of bleeding.
The best protection is to protect yourself from mosquitoes both by using repellents and insecticides, and by destroying potential breeding grounds for mosquitoes such as stagnant water reservoirs around and in homes.
To protect those around them, an infected person must take great care to protect themselves against bites so that they do not transmit the virus to other mosquitoes.