How long does dengue fever last? Contagious?

Since the summer of 2022, dengue fever cases have been increasing in France with the proliferation of the tiger mosquito. From May 1 to September 1, 2023, 557 cases have been identified in mainland France, according to Public Health France. Dengue fever worries but what is this disease ? How is she diagnosed ? How does it manifest and how long does it last?

Dengue fever: an often mild disease

Dengue is a viral disease caused by a arbovirus that is to say a virus transmitted to humans by insectsin this case here by the mosquitoes (female) of the genus Aedesmainly the species Aedes aegypti and Aedes albopictusmore commonly known as tiger mosquito. It’s a disease very often benign. In people who have been infected, healing results in lifelong immunity against the serotype causing the infection, but not against the other three. An individual can therefore be infected with each of the four dengue serotypes during their lifetime.

What are the symptoms of dengue fever?

There dengue fever is asymptomatic in 50 to 90% of cases (variable percentage according to the epidemics). Symptoms are most often flu-like:

• sudden high fever,
• headache,
• joint and muscle pain
• nausea/vomiting,
• rash resembling that of measles.

Symptoms appear within 3 to 14 days following the mosquito bite.

► The acute phase lasts about a week.

► A critical phase can occur between the 4th and 6th day approximately ; the swarning signs are a fever >39°C after the 5th day, severe abdominal pain with or without diarrhoea, uncontrollable vomiting, restlessness or drowsiness, edema, haemorrhagic signs. Most often benign although debilitating, classic dengue can however be complicated by hemorrhagic forms.

How long does dengue fever last?

Dengue is evolving over a week to 10 days. There fatigue may persist for several weeks. Healing is accompanied by a fortnight’s convalescence.

Dengue virus is transmitted by Aedes aegypti and Aedes albopictus mosquitoes.

What is the incubation period for dengue fever?

There Dengue fever incubation period ranges from 3 to 14 days : 4 to 7 days on average.

Is dengue fever contagious?

The person infected with dengue fever is not contagious for another human being, on the other hand it can contaminate other mosquitoes of the genus Aedes if it is bitten again in a period ranging from 1 to 2 days before the onset of symptoms and up to 7 days later.

We catch dengue fever after an infected tiger mosquito bite. The vector of dengue virus is Aedes aegypti mosquito and the tiger mosquito Who live in urban areas and breed mainly in containers with standing water. In Aedes aegypti, cis the female that stings, mainly during the day, with a peak of activity in the early morning and evening before dusk.

A person infected with dengue is not contagious to another human being.

► 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 a few days later. Once in the body, the virus multiplies and persists for 3 to 10 days. The virus can, more rarely, be transmitted by transfusion or transplantation (of organs or cells).

Who is at risk for dengue fever?

Dengue affects infants, young children and adults alike. So there are no people at risk more than others. Nevertheless, people living in areas with high circulation of the virus (see below) are most at risk.

Early diagnosis can be made by search for NS1 antigen, a dengue virus protein detected in the serum of people with dengue at the onset of fever; the identification of the virus can also be carried out early.
There search for IgM-type antibodies, only becomes positive around the 6th or 7th day of fever and persists for an average of 2 to 3 months. Other more sophisticated biological examinations, PCR-type or viral cultures are reserved for research or highly specialized laboratories in reference centres. “The biological diagnosis allows the declaration of the disease; on the other hand, if we accept the theory according to which a second infection could be more severeit is preferable for a person to know whether or not they have already had an episode of dengue fever, in order to adopt even more drastic preventive measures”, says Professor Anna-Bella Failloux. Blood samples can be taken in analysis and medical biology laboratories.

What are the treatments for dengue fever?

There is no no specific treatment dengue. The treatment is symptomatic, intended to fight against pain and fever. THE nonsteroidal anti-inflammatory drugs (ibruprofen…) and especially aspirin are contraindicated due to thrombocytopenia (decrease in the number of platelets) and hemorrhagic risk.

Is there a dengue fever vaccine?

There is no vaccine against dengue fever. Prevention therefore relies on effective vector control measures.

According to the ARS, to avoid mosquito bites, it is advisable to:

• wear covering and ample clothing, even to impregnate them with insecticide for fabrics;
• use a skin repellent, preferably in the morning and evening, recommended by a pharmacist, on exposed areas of skin;
• if necessary, use mosquito nets on the openings (doors and windows);
• using crib nets for newborns;
• use electric diffusers inside homes;
• use insecticide coils only outdoors;
• use air conditioners or fans that interfere with mosquitoes.

To limit the development of mosquitoes around your homeit is right to :

• empty, store or dispose of any container that may contain water;
• cover water supplies with a mosquito net or cloth to make them airtight;
• clean gutters and gutters;
• avoid illegal dumping of waste.

Is dengue fever dangerous for pregnant women?

Dengue virus infection during pregnancy does not cause no increased risk of disease or worsening disease in the mother. The rate of malformations is not increased, but occasionally cases of congenital dengue fever are observed. Premature births and abortions are possibly more common in dengue patients. Infection of the fetus occurs before birth, during the last weeks of pregnancy.

Is dengue fever dangerous in children?

In children under 15 years old, hypovolemic shock may set in (cooling, clammy skin and imperceptible pulse signaling circulatory failure) and lead to abdominal pain. Appropriate medical treatment is necessary to avoid complications and the risk of death. An intravenous infusion must be started quickly to restore the blood volume because haemorrhages can lead to significant blood loss.

Can you die from dengue fever?

Severe dengue is a life-threatening complication by the occurrence of a State of shock or bleeding complications. Generally after the resurgence of fever, the infection starts again and can evolve in rare cases (1% of cases in people with dengue symptoms) to severe dengue. Clinical vigilance should be maximal around the 4th day. The dengue usually heals within 2 weeks, but recovery time may take several weeks. Patients may feel quite tired during this period and develop depressive symptoms.

Produced with Professor Anna-Bella Failloux, head of the “Arboviruses and Insect vectors” research and expertise unit at the Institut Pasteur.