Yellow fever: What is this disease?How to prevent it?

Yellow fever is a serious viral hemorrhagic disease that rages in certain tropical regions of the world.Vaccination, the only effective weapon against the disease, is highly recommended for travelers passing through endemic zone.Some countries condition entry into their territory to obtain an international certificate of yellow fever vaccination.

Definition of yellow fever

Yellow fever is an acute viral hemorrhagic disease present in the tropical regions of Africa, South America and Central America.

Transmitted by vectors mosquitoes, the yellow fever virus causes acute hepatonephritis in its typical form (simultaneous involvement of liver and kidneys) which manifests itself by fever, headache, a reduction, muscle pain, jaundice(or jaundice) and vomiting.

Worldwide, this serious disease affects around 200,000 people a year for 30,000 deaths, especially in children (source 1).

In France, the disease can be imported in a sporadic and temporary manner by travelers who have stayed in endemic areas.

Vaccination is an effective and economical means of prevention.A single dose makes it possible to confer immunity for life against the disease.

The causes of this tropical disease

Viral disease

The yellow fever virus (or Amaril virus) belongs to the genre of flavivirus (such as dengue viruses, Japanese encephalitis, and Western Nile fever).It is a very small monocatennial RNA virus (40 Nm in diameter), with antigenic variations behind several African or American strains.

The yellow fever virus is an arbovirus (arthropod-boom virus);This means that it is transmitted by hematophagous arthropod vectors.These viruses are therefore able to cross the species barrier and are often the cause of zoonoses.

A monkey disease transmitted by mosquitoes

Among mammals, monkeys living in tropical region are natural and asymptomatic hosts of yellow fever virus.

In this natural cycle (or wild), the transmission between monkeys is made through the mosquitoes present in the tropical forests of these regions (Aedes in Africa and Haemagogus in Central America and South America).

Under these conditions, humans can also be infected with the virus as an exceptional "accidental" host when it moves in these forests, is bitten by infected mosquitoes and develops a yellow fever called "Selvatique".

Epidemiological circumstances

Epidemiological circumstances may cause epidemic waves depending on the environmental conditions and the immunity of populations:

Symptoms of yellow fever

Once the virus is inoculated by the bite of an infected mosquito, the incubation time is short: from 3 to 6 days.

In the majority of cases, the infection is asymptomatic or in form attenuated with influenza symptoms which disappear after a few days.

But for some patients, the disease evolves in a few days towards a serious hemorrhagic fever.This typical shape of yellow fever evolves in 3 phases:

- The "red phase" appears suddenly after the few days of incubation with fever (39 ° C), chills, headache, muscle pain and a congestive facies (redness at the level of the face, neck andthorax).At this stage of the disease, and in the context of a differential diagnosis, the clinic can also make fluid, dengue or malaria suspect.

- A fleeting remission of around 24 hours occurs 2 to 3 days after the appearance of the first symptoms with a transitional drop in fever.

- The "yellow phase" is marked by the reappearance of a high fever (40 ° C);It causes acute hepatonephritis (liver and kidneys) leading to hemorrhagic syndrome and cytolytic or jaundice (explaining the name of the disease).The patient can:

In its typical form, yellow fever is lethal in a few days (7 to 10 days) for almost half of the patients (source 2).The death occurs after episodes of convulsions, delusions and coma.

The survivors of the disease have a long convalescence but without sequelae.

All curable forms of Amaril virus infection lead to strong and lasting immunity (probably for life).

Prevention advice

Vaccination in endemic zone

Anti -star vaccination is made possible by researchers from the Dakar Pasteur Institute since 1932. Elle est le moyen de prévention le plus efficace pour éviter de contracter la maladie : > 90% de personnes protégées (source 3).A single injection makes it possible to obtain protective immunity after 10 days and for a period of 30 years (or even for life).

In endemic areas, and in particular those where immunity and vaccination coverage are low, the anti -marilier vaccine is essential to prevent or counter yellow fever epidemics:

Travelers' vaccination

In France, vaccination against yellow fever is compulsory for people (adults and children over 12 months old) residing or traveling to Guyana.Otherwise, it is particularly recommended for travelers going to countries at risk.

In addition, some countries require an international yellow fever vaccination certificate for obtaining a visa and entry into their territory.

Map of African areas affected by yellow fever (in English) map of South America areas affected by yellow fever (in English) list of countries requiring the certificate of vaccination against yellow fever

Contraindications to the anti-marilier vaccine

Be careful, the anti-marilier vaccine is a living attenuated vaccine, which in principle is contraindicated in:

Each situation must be considered on a case -by -case basis depending on the risk of exposure and must be the subject of an opinion from the attending physician.

In this regard, vaccination and obtaining the yellow fever vaccination certificate can only be carried out in a anti -arch vaccination center approved by the health authorities.

Note that "the anti-mail vaccine had formerly to be redone every 10 years but since 2016, except in some cases (including children under two, immuno-depressed people and pregnant women at the time of the first injection), it is valid for life ", according to Doctor Schérifa Salifou Laurain, general practitioner and mesotherapist.

Fight against mosquitoes vectors of the disease

The risk of transmission can be reduced by fighting against mosquitoes vectors of the disease.Individual protection measures (insecticides, covering clothes, mosquito nets, etc.) can be useful, but are rarely sufficient.

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Examinations: the diagnosis of yellow fever

Non -exhaustive clinical examination

The diagnosis of yellow fever is difficult, especially at an early stage of the disease.On the clinical level, other pathologies with damage to liver or renal predominance can be integrated into differential diagnosis: malaria, dengue, hepatitis, leptospirosis, measles (in children) or other viral hemorrhagic fevers.

Additional examinations required

Laboratory techniques can confirm the diagnosis:

Jointly in the clinic, the evaluation of these biological parameters is a major element to establish a prognosis for the disease.

The treatments of this viral hemorrhagic fever

The vaccine is the only effective way to fight against the disease and its spread.In addition, the treatments for yellow fever are only symptomatic: they do not allow healing and do not prevent death.However, in the absence of effective antiviral treatment, early patient management improves survival rates.This consists among others:

Acknowledgments to Doctor Schérifa Salifou Laurain, general practitioner and mesotherapist, for his indications and corrections.

Source 1: "Yellow fever", Pasteur Institute

Source 2: "Yellow fever", WHO

Source 3: "yellow fever", info service vaccination

"Yellow fever, dengue, Japanese encephalitis and West Nile virose, 4 major arboviroses Yellow fever, dengue, Japanese Enceptitis and West Nile Virus Infection: Four Major Arbovirus Diseases", Abourgeade and Al., Sciencedirect

'The diagnosis of yellow fever', Patrice Bourré and Al., Sciencedirect

A lire aussiAuteur : Dora Laty, Journaliste santé bien-êtreExperte : Dre Schérifa Salifou Laurain, médecin généraliste et mésothérapeute Publié le