For a long time, vector-borne diseases have been seen as essentially tropical issues, or as conditions linked to international travel. That view is now outdated. In metropolitan France, infections transmitted by mosquitoes, ticks and other arthropods are steadily progressing, driven by climate change, evolving ecosystems and the spread of vectors.
The French epidemiological landscape is gradually entering a new phase: that of a local, seasonal and now recurrent vector-borne risk.
What is a vector-borne disease?
A vector-borne disease is an infection transmitted by a living organism called a « vector », most often a blood-feeding arthropod:
- mosquito,
- tick,
- sandfly,
- flea.
The vector carries the infectious agent from one host to another. The agents involved can be:
- viruses,
- bacteria,
- parasites.
In metropolitan France, two major groups currently dominate:
- tick-borne diseases;
- mosquito-borne arboviruses.
Ticks: an old risk, but expanding
Lyme disease: the leading vector-borne disease in France
Lyme disease is today the most frequent vector-borne disease in France. It is caused by bacteria of the Borrelia burgdorferi complex and transmitted mainly by the tick Ixodes ricinus.
The most affected areas are:
- forested regions,
- wetlands,
- mid-mountain areas.
Some regions show particularly high incidence rates:
- Grand Est,
- Bourgogne-Franche-Comté,
- Auvergne-Rhône-Alpes,
- Nouvelle-Aquitaine.
Clinical features
The early phase is dominated by:
- erythema migrans,
- flu-like symptoms.
Without treatment, disseminated forms may appear:
- neurological involvement,
- arthritis,
- cardiac involvement.
Lyme disease perfectly illustrates how environment, biodiversity and human health interact.
Tick-borne encephalitis: an emerging disease to watch
Tick-borne encephalitis (TBE) is caused by a flavivirus transmitted by ticks. Long considered exceptional in France, it is now identified in several regions:
- Alsace,
- Jura,
- Haute-Savoie,
- Alpine areas.
The disease may progress to:
- meningitis,
- encephalitis,
- sometimes lasting neurological sequelae.
Improvements in molecular diagnostics and surveillance have likely revealed viral circulation that was previously underestimated.
Other tick-borne infections
Ticks can also transmit:
- human granulocytic anaplasmosis,
- babesiosis,
- tularemia,
- some rickettsioses.
Although rarer, these infections seem to be better detected than before thanks to advances in diagnostic techniques.
The tiger mosquito: symbol of the new vector-borne threat
Aedes albopictus has, within a few years, become the main emerging vector in metropolitan France. Originally from Asia, it has remarkably adapted to European urban environments.
Today:
- it is established in most metropolitan départements;
- its progression northwards continues;
- its seasonal activity window keeps extending.
Unlike many traditional mosquitoes, it bites mainly during the day and breeds in very small volumes of stagnant water:
- plant saucers,
- rainwater collectors,
- gutters,
- discarded objects.
Dengue: the gradual installation of an autochthonous risk
Dengue has become a major public health concern. Every year, metropolitan France records:
- thousands of imported cases,
- but also episodes of autochthonous transmission.
In other words: some infections now occur without any travel abroad. The disease usually combines:
- fever,
- headaches,
- muscle and joint pain,
- marked fatigue.
In some cases, severe hemorrhagic forms may appear.
Chikungunya: autochthonous outbreaks becoming more frequent
Chikungunya is also transmitted by the tiger mosquito. The clinical picture features:
- high fever,
- sometimes extremely disabling joint pain,
- symptoms that can persist for several months.
In recent years, several autochthonous outbreaks have been identified in mainland France, notably:
- in the PACA region,
- in Occitanie,
- in Corsica,
- in Auvergne-Rhône-Alpes.
Recent evolution shows that France now has the ecological conditions allowing local transmission chains.
Zika and West Nile: risks under surveillance
Zika remains rare in mainland France but is still monitored due to:
- its risk of sexual transmission,
- and especially its teratogenic potential during pregnancy.
The West Nile virus, for its part, mainly circulates in Mediterranean areas. It is transmitted by mosquitoes of the genus Culex and has an avian reservoir. Most infections are asymptomatic, but some severe neurological forms can occur.
The major role of climate change
Global warming acts as an ecological accelerator. Several phenomena are observed:
- geographical expansion of vectors;
- increase in their density;
- longer activity seasons;
- improved winter survival conditions.
Milder winters and longer summers favor the durable settling of species previously confined to tropical or Mediterranean regions.
A « One Health » challenge
Vector-borne diseases perfectly illustrate the One Health concept. The circulation of infectious agents depends closely on:
- animal reservoirs,
- the environment,
- human activities,
- climatic changes,
- international mobility.
The health response can therefore no longer be purely medical: it becomes ecological, territorial and systemic.
What is at stake for healthcare facilities?
For hospital structures and infection prevention teams:
- better clinical recognition;
- integrating arboviruses into summer differential diagnoses;
- fast reporting;
- managing imported cases;
- training healthcare professionals;
- adapting risk maps.
In the medium term, vector-borne diseases could become a recurrent topic for:
- crisis management,
- environmental surveillance,
- and territorial public health preparedness.
How to protect yourself?
Against mosquitoes
- eliminate stagnant water;
- use suitable repellents;
- wear covering clothes;
- install mosquito nets.
Against ticks
- stay on marked paths;
- wear long clothing;
- inspect your skin after a walk;
- quickly remove ticks with a tick remover.
Conclusion
Metropolitan France is going through a deep transformation of its vector-borne landscape. The tiger mosquito is settling durably. Autochthonous arboviruses are multiplying. Tick-borne diseases remain very frequent.
The main change is perhaps not only biological or climatic. It is also cultural.
We must now think of vector-borne diseases no longer as exotic and exceptional events, but as health risks fully integrated into our daily environment.
NutriCellScience, Mark DOWN — EN edition
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