Possible outbreak of dengue fever in Nice

Health authorities in the southern city of Nice are warning of a possible outbreak of native dengue fever spread by tiger mosquitoes after two cases were confirmed. Around a dozen others are suspected.

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Health agency l’Agence Régionale de Santé (ARS) for the Nice and Alpes-Maritimes region spoke of a possible “outbreak” for the first time this week, after one case of dengue fever was confirmed on Friday September 4, and another on Monday September 7.

The use of the word “outbreak” signals that at least a dozen other suspected cases are currently being investigated.

The cases are being considered as “native” infections, meaning that the people with a confirmed or suspected case have not travelled to a known dengue risk area within the past 15 days.

They are therefore thought to have become infected after being bitten by a tiger mosquito (Aedes albopictus) in mainland France.

The first confirmed case in Nice was a resident of the Pessicart neighbourhood, while the second lived on Boulevard Mantega-Righia, to the west of the Boulevard de Cessole.

Both areas have now been “quickly de-mosquitoed” by specialist team L’Entente Interdépartementale de Démoustication, which acted on the public streets and in private gardens to try to eliminate all tiger mosquitoes from the district, said the ARS.

Local residents have also been given free information leaflets on how to reduce mosquito numbers and try to avoid being bitten. These include reminding people of the “importance of prevention measures to avoid bites, including wearing clothes outside that cover your skin, and using anti-mosquito products”.

Locals are also reminded to remove “anything [around the home or garden] that could contain stagnant water and therefore provide a base for mosquitoes to thrive”.

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These are not the first cases of native dengue fever in France. The mosquito - which used to be associated with the south - has been slowly spreading north in the past decade, and has now even been reported in Paris.

Since 2010, there have been at least 50 reported cases of dengue fever and chikungunya in people who have not visited countries where those illnesses are prevalent.

And in May 2020, mosquito alert agency Vigilance Moustiques warned that 57 French departments were on red alert for tiger mosquitoes.

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Increased risk to France

The Aedes albopictus, or tiger mosquito, is known to be a vector of illnesses such as dengue, zika, and chikungunya, even in mainland France.

These diseases “will represent a major health risk across the country...over the next few decades”, a health commission told the French Assemblee Nationale at the end of July. The commission called for tough measures against the insect.

In its report, MP Ramlati Ali said: “This is an invasive species, which did not exist in France before 2004. In 2019, 58 out of 96 mainland departments were affected. The mainland has been sheltered from mosquito-borne illnesses for 50 years, but this is no longer the case today.

“We must learn to live with them, and limit their impact on the health of residents in France.”

Dengue fever: The symptoms

Dengue fever originated in tropical regions. It causes high fever, muscle pain, headaches, eye pain, and fatigue, and can be fatal in some severe cases. However, between 50-90% of cases are asymptomatic.

The ARS has advised people in the area that if they notice any of the symptoms above - and especially after a recent mosquito bite - to immediately call their GP.

A rising fever

Dengue is also on the rise globally, according to the World Health Organisation.

Cases have increased eight-fold over the past two decades across the world, rising from 500,000 reported cases in the year 2000, to more than 2.4 million in 2010, and 4.2 million in 2019.

The number of deaths rose from 960 in 2000, to 4,032 in 2015.

Anti-mosquito initiative

A number of initiatives across the world are seeking to reduce the negative impacts of the tiger mosquito and the diseases it spreads, including one major non-profit project, The World Mosquito Program (WMP).

The WMP is an Australian research initiative that was first started 10 years ago, and is partly financed by the Bill and Melinda Gates Foundation.

Bruno Col, project spokesperson, said that the initiative is seeking to “use the mosquitoes against themselves”.

The main aim is to inoculate the female insects with a natural bacteria named “Wolbachia”, which is “present in 60% of insects across the world”.

Dr Anna-Bella Failloux, entomologist (insect expert) and head of the Arboviruses and Insect Vectors Unit at the Institut Pasteur in Paris, explained to news source HuffPost: “[This bacteria] shortens the life of the female mosquito and reduces the risk that the mosquito will be infected if it bites an infected person, so stops the spread via the mosquito.”

It does this because the bacteria and the virus “colonise the same environment” in the body, and find themselves “in competition with cellular resources”, making it less likely that a bacteria-infected mosquito will pick up the virus.

Similarly, the bacteria also works to reduce mosquito population numbers overall, as the young of a female carrier are unlikely to be viable, explained Dr Failloux.

The project has already successfully released mosquitoes carrying this natural bacteria in Australia, Brazil, Indonesia, and the French territory New Caledonia.

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