Less known than dengue or chikungunya, the Western Nile virus is gaining ground carried by increasingly early waves of heat.
If its name rather evokes Egypt it is in Europe that the Western Nile virus actively circulates (also called “West Nile”) this summer. The first indigenous case of the year was detected in mid-July in the VAR according to the reinforced public health surveillance bulletin France. Little known to the general public, the virus transmitted by Culex mosquitoes, very common in Europe, is not a newcomer. Last summer, 38 human cases were detected in France exclusively in the southern half, without making deaths. Discovered in the 1930s in Uganda in the 1930s the first European household was identified in Camargue in 1962.
If 80 % of cases remain asymptomatic, ” The symptomatic forms of the disease are characterized by the sudden appearance of a significant fever after 3 to 6 days of incubation ”, specifies the Pasteur Institute. These symptoms can also be accompanied by headache, rashes or vomiting. In 1 % of cases, the virus can tackle the nervous system and become fatal, especially for sensitive people (pregnant women, newborns, elderly) or comorbidity.
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Epidemic in Italy
Cases have also been identified in Greece, Romania and Bulgaria, but it is with our Italian neighbors that the virus is particularly virulent this summer. There are 13 dead of Western Nile fever, most of them in the past two weeks, especially in the regions of Naples and Rome. However, not enough to panic according to the Italian Ministry of Health which specifies that the ” virus has been endemic in Italy since 2008 ».
Even if the disease has been known and monitored for a long time, the particularity this year is that out of the 15 Italian regions affected, eight had never been before. “” It is due to the migration of infected birds which is unpredictable ”, Explain to Figaro Sylvie Manguin Director of IRD research and specialist in vector transmission infectious diseases (diseases transmitted by a vector, often an insect). “” Birds carrying the West Nile virus can migrate from one region to another ». The Culex mosquito, very widespread in Europe can then be infected and transmit the disease to a mammal, mainly horses and humans.
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Climate change
This year, early heat waves allowed mosquitoes to proliferate. “” If you have warmer temperatures, as we had in June, even in May, the mosquito development cycle will be done earlier “Explains the researcher. Thus, the period during which the mosquito will be able to transmit the virus, will be all the longer. “” Now we see that mosquitoes are starting to be active from April until early November. Statistically it increases the chances of having transmission Adds Sylvie Manguin.
In 2023, a study conducted in Greece and published in the review Nature demonstrated that climatic factors are the main engines of the dynamics of Culex Mosquito populations vectors of the West Nile virus. The latter are favored by long periods of hot climate and conversely too much precipitation, humidity and wind prevent their proliferation.
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Faced with the Western Nile Virus, there is a vaccine for horses, but none for humans. To fight against this disease, the ARS deploys means of prevention and communication as in last August in the PACA region where the inhabitants of the areas concerned were alerted by SMS.
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But above all, as for dengue and chikungunya, Sylvie Manguin recalls the need to practice demosters. “” As soon as a case is diagnosed, within 24 hours, there must be a fumigation of the zone, where the person has been prone to “, She explains recalling that there is no transmission of a man to a man or a man to a man.