Dengue fever circumstances are exploding in mainland France: what do that you must know?

Dengue fever circumstances are exploding in mainland France: what do that you must know?

An unprecedented variety of dengue circumstances have been recognized in mainland France since mid-summer. Certainly, almost forty “indigenous” circumstances – in different phrases, infections contracted on nationwide territory, with out the sufferers having traveled overseas – had already been reported in mid-September, which is greater than the cumulative whole of the final 10 years.

The illness has additionally declared itself in departments the place it had by no means been detected till now. Whereas the variety of infections will seemingly proceed to rise within the days and weeks to return, which areas are affected? What are probably the most believable causes of this distinctive scenario? And why can this example be worrying?

Within the Alpes-Maritimes, the most important outbreak ever recognized in metropolitan France

Presently, of the 5 departments affected by the illness, three are situated within the Occitanie area and two within the Provence-Alpes-Côte d’Azur (PACA) area.

In Occitania, 4 circumstances have been recognized in the identical habitat, within the city of Salvetat Saint-Gilles, 20 km west of Toulouse, in Haute-Garonne; 3 circumstances have been reported within the commune of Andrest and that, 15 km away, of Rabastens-de-Bigorre, within the Hautes-Pyrénées; 1 case was detected in Perpignan, within the Pyrénées-Orientales. The dengue virus had by no means been recognized in these final two departments.

Within the PACA area, the 2 departments affected are the Var, with six circumstances recognized in Fayence and, above all, the Alpes Maritimes with 26 circumstances recognized in three municipalities situated lower than 10 km away from one another: Saint Jeannet, Gattières and Gaude. The geographical and temporal proximity – they have been declared over a month – of those new circumstances leans in favor of a single and similar episode of circulation of the virus in these three municipalities. This focus is already the most important ever recognized in metropolitan France. It’s nonetheless lively, with the final circumstances recognized in early September. Different circumstances will seemingly be recognized quickly.

Till now, the variety of autochthonous circumstances of dengue fever remained very restricted in metropolitan France. It was estimated at lower than thirty because the first case recognized in 2010, with fairly often only some circumstances recognized per 12 months.

The variety of circumstances reported this 12 months due to this fact already exceeds all of the circumstances recognized over the previous 15 years.

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Word additionally that dengue is usually asymptomatic (in about 70% of circumstances), it may well go largely unnoticed. Moreover, with the Covid-19 pandemic, the analysis of different viral ailments has in all probability been underestimated over the previous two years. This will likely have involved particularly numerous arboviruses, together with dengue fever. The precise variety of circumstances is due to this fact in all probability tremendously underestimated.

Why such an explosion? Whereas it was troublesome to anticipate a rise within the circulation of dengue fever such because the one we’re experiencing in 2022, lately a number of precursors have foreshadowed a rise in vector-borne ailments.

The vector mosquito has invaded our territory

Distribution of the tiger mosquito in mainland France and Corsica, in January 2022.
Ministry of Solidarity and Well being

The virus that causes dengue fever is transmitted by mosquito species belonging to the genus Aedesof which the tiger mosquito is a component (Aedes albopictus). Nevertheless, since its first detection on our territory, in 2004 in Menton, this small black mosquito with a physique and legs striped with white native to Southeast Asia and the Indian Ocean has not stopped rising its French distribution space.

In lower than 20 years, it has invaded 67 out of 96 metropolitan departments (in comparison with solely 58 in 2020!). Its unfold all through the territory is inexorable.

Close-up photo of a female tiger mosquito feeding
The tiger mosquito is especially recognizable by its white striped legs.

The supply of serious discomfort in the summertime interval (some vacationer areas are infested with it), the tiger mosquito is able to transmitting, along with the dengue virus, numerous viruses chargeable for diseases in people, together with Zika or chikungunya virus. Its extension on our territory will increase the danger of spreading the ailments they trigger.

Presently, amongst these three viruses chargeable for tropical ailments, the dengue virus is probably the most current in metropolitan France, notably within the southern areas, the place the density of tiger mosquitoes is the best.

A danger elevated by environmental and climatic adjustments

Climate situations, particularly temperature, air humidity and precipitation, have an effect on the geographic distribution and exercise of mosquitoes. Specifically, they promote their proliferation and their lifespan.

The summer time we skilled, distinctive for its alternation of scorching warmth and intense wet episodes, notably within the southern areas, led to a major improve within the variety of mosquitoes.

Certainly, if their eggs want water to finish their growth course of, they’re however very resistant within the surroundings. Within the occasion of a drought, they will stay viable for as much as a number of years, permitting them to outlive till the situations for his or her hatching are favorable.

This explosion in mosquito populations has elevated the danger of transmission of the dengue virus, itself already elevated by the resumption of worldwide commerce and tourism.

Tourism and commerce promote the unfold of pathogens

Industrial or vacationer exchanges, which have been rising exponentially for a number of a long time, can facilitate the unfold of viral ailments, and particularly ailments unfold by vectors comparable to mosquitoes.

Proof of the significance of those elements, through the Covid-19 pandemic, the variety of circumstances of dengue fever infections from folks getting back from journey exterior the Antilles decreased significantly, primarily as a result of drastic drop in worldwide air transport. With the marked restoration in air visitors this 12 months, a rise in imported circumstances has been noticed: from 1is Might to September 2, 2022, Public Well being France counted 165 imported circumstances of dengue fever in France, already as many as for the entire of 2021…

These imported circumstances are as many dangers of the looks of “native” outbreaks, when the mosquito vector of the illness is current on the spot. And this, particularly since dengue fever is the commonest and widespread arbovirus on the planet.

How is dengue transmitted?

Originating in Africa, the dengue virus is a arbovirusfrom the English “ARthropod-BOrne VIRUS”, a virus transmitted by bugs that feed on blood. It belongs to the genus flaviviruscomparable to Zika virus, or yellow fever and West Nile viruses, different arboviruses.

When a mosquito bites an contaminated individual, it ingests the blood through which the dengue virus is current. The latter will then multiply within the physique of the mosquito, which can transmit it to a different particular person throughout a brand new chunk.

The primary circumstances of dengue have been listed within the XVIIIe century on the American continent. This situation is well-known in lots of tropical and subtropical areas of the globe, from Africa to Asia by way of Latin America. The French abroad territories should not spared: Reunion, Guadeloupe or Martinique have suffered recurrent epidemics lately.

A illness that’s usually asymptomatic, however generally severe

Dengue fever is usually known as “tropical flu”, as a result of its signs are most frequently flu-like: sufferers have fever, complications, physique aches… They will additionally generally develop a rash.

Manifestations of the illness happen 3-14 days after the mosquito chunk, with a median of 4-7 days. The affected person typically recovers spontaneously in a couple of days, however vital fatigue persists for a number of weeks.

Dengue virus particle transmission electron microscopy image
Dengue virus particles, spherical and darkish, are clearly seen on this picture taken with a transmission electron microscope.
Frederick Murphy/CDC

Presently, there isn’t any particular remedy for dengue fever. A vaccine exists (Dengvaxia), nevertheless it stays little used as a consequence of many limitations relating to its use. This vaccine has the drawback of accelerating the danger of hospitalization and extreme dengue in folks not beforehand contaminated with the dengue virus. It’s primarily prescribed to folks dwelling in endemic areas, and who’ve already been contaminated with the dengue virus.

The administration of the illness consists primarily of treating the signs, particularly ache and fever. Aspirin and non-steroidal anti-inflammatory medicine are formally contraindicated as a result of danger of bleeding.

The primary drawback related to dengue fever is the danger of growing what is known as extreme dengue fever or dengue hemorrhagic fever, which could be sophisticated by a state of usually deadly shock. Dengue hemorrhagic fever is manifested particularly by respiratory misery related to a number of hemorrhages.

Thankfully, this extreme type of dengue impacts solely a small share of contaminated folks: between 1% and 5% of circumstances. Some folks additionally develop extreme neurological injury (comparable to encephalitis) however these issues are extraordinarily uncommon.

4 totally different virus varieties, however no cross-immunity

There are 4 various kinds of dengue virus, that are differentiated from one another by delicate adjustments of their antigens (antigens are buildings whose detection by the immune system results in its response and the manufacturing of antibodies – it may well s act of proteins, lipids, sugars, and so forth.).

These 4 dengue virus serotypes, named DENV-1, DENV-2, DENV-3 and DENV-4, though comparatively comparable, are totally different sufficient to not confer long-term cross-protection. In different phrases, if an infection by one of many serotypes immunizes us in opposition to it, it doesn’t supply safety in opposition to the opposite three. You’ll be able to due to this fact be consecutively contaminated with the 4 dengue serotypes throughout your lifetime.

In mainland France, a minimum of two serotypes, DENV-1 and DENV-3, have been recognized this 12 months. Which means the dengue virus has been launched into the territory a number of occasions this summer time.

Mosquito management as a way of prevention

After the invention of circumstances of an infection, the identical situation takes place: mosquito management operations are carried out close to the circumstances detected, accompanied by awareness-raising actions with the general public and well being professionals (in addition to throughout surveys door-to-door), carried out in collaboration with the ARS, Public Well being France and mosquito management companies comparable to Altopictus or the Interdepartmental Mosquito Management Settlement.

Presently, the most effective methods to stop the unfold of viruses comparable to dengue, transmitted by mosquitoes, is to restrict the proliferation of those bugs and to guard themselves from their bites.

To scale back the event of mosquito larvae, it is suggested to empty all containers of stagnant water, together with flower pot cups and watering cans, and to cowl rainwater containers, particularly in periods of heavy rainfall. . To restrict the danger of being bitten, it is suggested to make use of appropriate repellents, and to put on free and overlaying clothes.

Thankfully, in our nation, the specter of arboviruses, together with dengue fever, stays sporadic in the interim and the danger of an epidemic is restricted. Strengthening surveillance networks at present stays top-of-the-line methods for combating these new threats which can be troublesome to anticipate.

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