Mosquito control operations across France: how this may impact your commune
More than a thousand operations were carried out in southern France last year
Residents across France should be aware of the increasing prevalence of anti-mosquito operations as the summer period begins.
These operations, which see authorities spray zones with chemicals to eliminate mosquito populations, have become more important as the threat of tropical diseases in mainland France grows.
The first two native cases of Dengue Fever this summer have sparked a renewed awareness over the insects.
Tiger mosquitoes, an invasive species to France now present in all regions, can transmit tropical diseases including Chikungunya and Zika Virus alongside Dengue Fever.
However, native Culex mosquitoes can also spread diseases including West Nile Virus.
‘Native’ cases relate to patients who contracted the illness despite not leaving France for 15 days prior, meaning they were infected by a mosquito in France.
How do cases spread?
Mosquitoes that feed on an infected person (who has been infected abroad and imported the disease to France) become vectors for the disease.
In turn, they can spread the disease to anyone they feed on.
This can lead to several generations of mosquito spreading the disease in a close area, feeding off of infected people and infecting new ones.
Incubation periods for the disease vary. For example, Chikungunya is not transmissible for three days until after infection, but for Dengue Fever it usually takes up to two weeks.
In any case, the period at which transmission of the diseases from humans to mosquitoes (the viremia period) for the diseases begins two days before symptoms appear and can last up to seven days, meaning people can unknowingly spread the disease before they even notice they are ill.
It also means that by the time a case has been declared, there is already a risk that the chain of transmission is deep within a community.
Rapid response
When a case of any tropical disease is confirmed, an investigation is opened and authorities act quickly to destroy the chain of mosquitoes able to spread these diseases in the area.
If action is not taken quickly, outbreaks can be massive.
Last summer 809 native cases of Chikungunya were recorded in France, from 79 outbreaks. A single outbreak was responsible for 144 cases.
Residents in the area will be urged to tackle mosquito populations in their homes and gardens, but authorities also move to bring in professional aid.
The decision to officially carry out an operation in an area is decided by the Agences Régionales de Santé (ARS, regional health authorities), who then pass the task on to a local agency responsible for treating an area.
An area must fulfil two conditions for an operation to take place:
A confirmed case of Dengue Fever, Zika Virus, or Chikungunya must have been reported. These diseases are ‘notifiable’, meaning doctors must declare them to regional authorities. It applies to both ‘native’ and ‘imported’ cases, where a person was infected abroad
The departments must be confirmed to host tiger mosquitoes
Last year, only three regions did not see anti-mosquito operations take place (Brittany, Normandy, Hauts-de-France).
In the south, 631 operations were carried out in Provence-Alpes-Côte d'Azur, 338 in Nouvelle-Aquitaine, and 281 in Occitanie.
Operations are usually carried out within 48 hours of a case being declared.
It is possible for private companies to conduct their own operations – there are no rules against this – and indeed some businesses hire pest control companies for regular operations.
The most common clients include holiday and leisure resorts, restaurants, but also local authorities and public buildings.
However, there have been calls for limits on the number of private operations not managed by the ARS for a number of reasons.
Firstly, the chemicals used are powerful insecticides that do not target only mosquitoes but all insects, and can have a negative effect on local wildlife.
These chemicals can be in short supply, and there are arguments that the ARS should have priority on them in case of any shortages.
Also, a liberal usage of these sprays risks increasing immunity in native mosquito populations, making it harder to eliminate them in the future.
How does process happen? What must residents do?
Once the ARS confirms a treatment in an area, the agency responsible will track the history of a victim to see if they can pinpoint where they were infected.
They will check homes, workplaces, shops they visited, etc, ruling out places where there are no mosquitoes or where mosquitoes are unlikely (air-conditioned buildings or offices several floors up rarely see mosquitoes).
Zones where there is a risk of transmission are treated within a 150 metre radius – mosquitoes rarely travel further than this in their lifetimes, unless accidentally transported.
One exception to this is a buffer zone around bodies of water, protected by a 25m - 50m radius, and certain regions have their own restrictions (in Île-de-France for example, vegetable gardens are typically excluded from being sprayed).
Treatments can take place in both public and private areas within the radius, meaning homeowners and residents can be impacted.
Residents in the area will be informed of an incoming operation without being told the precise zone, to keep the identity of the patient anonymous.
While they can refuse for a treatment to be carried out, authorities will attempt to explain the importance to them.
“They usually agree when we explain that a neighbour has Chikungunya and that they could catch it, though we sometimes spend a lot of time convincing certain residents,” said medical entomologist who engages in such treatments Grégory L’Ambert to media outlet Le Monde.
If people remain unconvinced, the prefect can issue a formal notice to allow authorities to spray the area, but this can delay proceedings and reduce the effectiveness of a treatment.
Chemicals are sprayed at night to reduce environmental and human impact (bees are sleeping at this time, and humans should not be within inhalation range of the chemicals).
Night-time activity is also important as tiger mosquitoes are typically resting at this time (unlike Culex mosquitoes they are diurnal and bite during the day), so are easier to destroy.
Residents are advised to take a series of precautions to minimise the impact of the spraying.
Before the operation they should bring pets, laundry, and toys indoors, and move or protect beehives. Note that cold-blooded animals are more sensitive to the deltamethrin chemical used, so should be given more protection.
During the treatment, people stay indoors with windows and doors closed. This is usually the case as operations are carried out at night, but you should still make sure there is no incoming airflow.
The next day; rinse garden furniture and outdoor toys/equipment with water (if waterproof), and wait three days before eating fruits and vegetables from the garden, regardless if rinsed or peeled.
