The dengue virus, or tropical flu, predominantly in the intertropical zone, belongs to the flavivirus family, such as the Zika virus, yellow fever, West Nile, etc. These are arboviruses (abbreviation of arthropod-terminal viruses), because they have the peculiarity of being transmitted by arthropods, blood-sucking insects like 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 one can not be contaminated a second time with a virus of the same serotype, but it is possible to contract a dengue due to one of the other three types. According to a hypothesis supported by WHO, a second infection with another serotype is ten times more likely to develop a severe form than during a first infection, but this theory is currently disputed by many experts. Dengue is the most common type of human arbovirosis with 50 to 100 million cases a 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 never stops to expand as a result of uncontrolled urban development, increased international trade and climate change. The virus has spread particularly in the French departments of America (Guyana, Guadeloupe, Martinique) as well as in Polynesia,
What are the causes of the disease, the mode of transmission of the virus?
The main vector of the dengue virus is the mosquito Aedes aegypti lives in urban areas and breeds mainly in containers containing stagnant water. It is the female that 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 Aedes albopictus (or “tiger mosquito” that also transmits chikungunya), with diurnal activity, present in Asia and spread to North America and Europe. Equipped with great ease of adaptation in temperate zones, it was introduced in 2004 in the Alpes-Maritimes, and its area of implantation continues to expand.
The mode of contamination is traditional: the mosquito is infected by pricking an already infected person and can transmit the virus by pricking another person. Once in the body, the virus multiplies and persists for 3 to 10 days. The person infected with dengue fever is not contagious to another human being, but can infect other Aedes mosquitoes if they are stung again in a period of 1-2 days before the onset of symptoms. until 7 days later.
The symptoms of dengue fever
Dengue manifests itself as a “tropical” flu, with at the beginning:
– a high fever of sudden occurrence,
– muscular and articular pains,
Two or three days later:
– the fever drops before going back up
– a very characteristic rash, similar to measles appears in one out of two cases of one,
– some bleeding from the skin and / or mucous membranes (mucocutaneous bleeding) occur. These bleeds may occur as spontaneous hematomas (blue on the skin), petechiae (small red dots on the surface of the skin), bleeding nose, bleeding gums, vomiting blood or blood in stool.
Most often she progresses to regression and healing in 4 to 5 days, leaving some fatigue. Dengue affects people of all ages. The disease occurs within 3 to 14 days after the bite of the mosquito (4 to 7 days on average) following the bite by the mosquito.
Dengue is in the vast majority of cases benign
– it can even go unnoticed in 50 to 90% of cases
– but often disabling by pain and fever. The major risk is that of severe dengue, with haemorrhagic complications or shock.
Dengue importation is relatively common in metropolitan France. It is necessary to consult a doctor in case of a fever or influenza-like illness occurring a few days after the return of a trip to a tropical zone, which may correspond to a dengue fever, but also to chikungunya or malaria. People living in a Aedes albopictus dissemination zone in France should also consult with suggestive signs, since “native” dengue occurring in subjects who have not traveled is not uncommon.
In all cases, the doctor will look for signs of potential severity, hemorrhages of the skin or mucous membranes, blood pressure drop, and thrombocytopenia (decrease in the number of platelets on the blood count)
Since 2007, in France, dengue fever has been a notifiable disease.
How is the diagnosis made?
Early diagnosis can be made by looking for the NS1 antigen, a dengue virus protein detected in the serum of people with dengue fever as soon as the fever appears; the identification of the virus can also be done early.
The search for IgM antibodies is positive only around the 6th or 7th day of fever and persists for an average of 2 to 3 months. Other more sophisticated biological tests, such as PCR or viral cultures, are reserved for research or highly 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 may be more severe, it is better for someone to know that they have already had an episode of dengue, so that they can take even more preventive measures. draconian.
What is the evolution of dengue fever? Its complications?
Severe dengue fever is a life-threatening complication due to the occurrence of shock or haemorrhagic complications. Generally after the outbreak of the proud, the infection starts again and can evolve in rare cases (1% of cases in people with dengue symptoms) to severe dengue fever. Clinical vigilance should be maximal around the 4th day.
In the haemorrhagic form, the blood accumulates in the cutaneous vessels, the rash becomes haemorrhagic and we observe petechiae (small red-purplish cutaneous spots, related to the infiltration of blood under the skin) , bruises (hematoma)sometimes accompanied by mucous or internal bleeding, digestive or cerebral in particular.
The unfavorable evolution can also be made to a state of shock: the liquids of the organism leave the vessels, going to accumulate in various organs, causing edema, effusions of pleura, 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 import dengue, they can occur at any age and in any individual, but will be more severe in the most vulnerable. The management of these severe forms is done in the middle of resuscitation to compensate for the various failures. Thus, the mortality of these severe dengue fever is very low in countries where health facilities are developed, but can reach 10 % in countries without adequate resuscitation structures.
What are the treatments ?
There is no specific treatment for dengue. The treatment is symptomatic, intended to fight against pain and fever. Nonsteroidal anti-inflammatory drugs and especially aspirin are contraindicated because of thrombocytopenia (a decrease in the number of platelets) and the risk of haemorrhage.
Can we prevent the disease?
The best protection is to protect themselves from mosquitoes ( cf card Passport Health (. Http: // www . Passeportsante . Net / en / News / interviews / sheet . Aspx ? Doc = interviews mosquito ) both by the use repellents and insecticides, and the destruction of the cottages potential for mosquitoes like stagnant water tanks around and in homes
to protect his entourage, the sick person must strictly guard against bites so that it does not transmit the virus to other mosquitoes.
Several vaccine candidates are currently under development and the first dengue vaccinations started this year, with a first vaccine for dengue prevention, Dengvaxia is now administered in the Philippines at three doses in one year. It is a tetravalent vaccine, which therefore protects against the 4 serotypes , and is also registered in Mexico, Brazil and El Salvador most affected countries of America. The vaccine should be available first in high-endemic countries.