Why one south-west France village is overrun by mosquitoes
'Several thousand larvae per square metre' in lake after flooding
Thousands of mosquitoes have descended on the Mediterranean village of Leucate (Aude) after an unusual combination of sea winds and rising water levels triggered a mass hatching around the nearby lagoon.
Local authorities say the outbreak is temporary and should ease over the coming days, although residents are currently experiencing its peak.
The outbreak comes as France remains under heightened mosquito surveillance during the summer, with health officials already recording locally acquired cases of dengue and West Nile virus in Occitanie this year.
Rising lagoon waters caused mass hatching
The Leucate mairie says the invasion was caused by "particular natural conditions" around the Etang de Leucate.
Since early July, sea winds have gradually raised water levels in Mediterranean coastal wetlands. During the weekend of July 11, more than 250 hectares around the Etang de Leucate were flooded.
The flooding triggered the mass hatching of Aedes caspius mosquitoes, with "several thousand larvae per square metre" recorded in some areas.
Unlike the Asian tiger mosquito (Aedes albopictus), which can spread diseases including dengue and chikungunya, Aedes caspius is a native saltmarsh species mainly regarded as a biting nuisance.
Mosquito control unable to eliminate all insects
A total of 29 hectares in Leucate and a further eight hectares in neighbouring Le Barcarès, Pyrénées-Orientales, were treated by air on July 15 and 16.
However, a small proportion survived the treatment.
"These 'residual' mosquitoes are responsible for the severe nuisance currently being experienced," the mairie says.
According to EID Méditerranée, the area is now at the height of the outbreak, which is expected to gradually subside and return to normal over the next few days.
France remains on alert for mosquito-borne diseases
Since May 1, public health agency Santé publique France has recorded 231 imported dengue cases, 80 imported chikungunya cases and eight imported Zika cases.
Two locally acquired dengue infections have also been identified this year, in Tarn and Hérault.
Unlike dengue and chikungunya, West Nile virus is spread by Culex mosquitoes, which are widespread across mainland France.
When imported or locally acquired cases of dengue, chikungunya or Zika are detected, health authorities carry out epidemiological and entomological investigations and, where necessary, order targeted mosquito control operations to reduce the risk of local transmission.
Around locally acquired cases, insecticide treatments are expanded and active case-finding may be carried out, including door-to-door enquiries and alerts to local healthcare professionals.
Residents still urged to remove standing water
Although the outbreak in Leucate stems from flooded coastal wetlands rather than gardens, residents are still urged to remove standing water around their homes to limit breeding by Asian tiger mosquitoes.
Likewise, people across France are advised to remove standing water wherever possible by regularly emptying plant pots, buckets and other containers, covering water butts, maintaining gutters and drains, and clearing anything that could collect rainwater.
