2023-07-06 23:11:20
After dengue or chikungunya, might Reunion be affected by the West Nile and Usutu viruses? Indeed, researchers from the Paster Institute have revealed that the tiger mosquito is now capable of transmitting these two new viruses. But while this discovery was made, Imaz Press questioned the Research Institute for Development (IRD) and the Regional Health Agency (ARS) on the epidemiological risks in Reunion. (Photo RB/www.imazpress.com)
For the time being, no risks for Reunion, wishes to reassure the Regional Health Agency. “These diseases are not currently identified in Reunion.”
“These are diseases mainly affecting animals (birds, horses), which cannot be transmitted from man to home, including via a vector”, tells us the ARS.
However, “the Culex mosquito – a natural vector of these viruses – was abundant in Reunion”, indicates Patrick Mavingui, research director at the IRD. The director who adds: “it is not excluded an introduction of these viruses on the island, either by viraemic people (who have the virus in the blood), or by infected wild birds, with in addition a passage in poultry”. “Which would increase the risk of epidemic emergence,” adds Patrick Mavingui.
A fact confirmed by the Regional Health Agency. “The two viruses are already present on the national territory. There are few migratory birds that come to Reunion (two species of falcons, a few waders, crows and more recently glossy ibis).” “All these birds are known to be able to transport and amplify the West Nile virus,” says the ARS. “The mosquitoes present in Reunion are also potential vectors of these diseases. So yes, theoretically, the risk for Reunion cannot be excluded.”
– The tiger mosquito, carrier of these viruses –
It is as part of a monitoring study of mosquitoes carried out in the Grand Est region that the Institut Pasteur researchers made this discovery.
“The tiger mosquito Aedes albopictus (which is found mainly in Reunion) has already been found naturally infected by the West Nile, for example in Pennsylvania”, explains the director of the Research Institute for Development, Patrick Mavingui .
“Experimental (therefore artificial) infections showed that Aedes albopictus were permissive to infection by 22 arboviruses (viruses transmitted to humans by mosquitoes from an animal reservoir or an infected individual), including West Nile and Usutu. That is to say, when we feed the females of this species with blood containing live virus, the infectious virus is found in its saliva. We then say that the mosquito is competent for this virus”, explains the scientist.
“These experiments therefore suggest that the tiger mosquito is potentially capable of transmitting these different viruses,” he concludes.
– An unexpected discovery –
“Many of our results were predictable, except for the tiger mosquito Aedes albopictus,” says Anna-Bella Failloux, coordinator of the study which aimed to measure the abilities of five species of mosquitoes to transmit West Nile and Usutu viruses. .
To explain this unexpected discovery, a track is put forward and points to the important role of migratory birds. Indeed, each year, in the spring, millions of birds make a long migration to reach their breeding grounds, passing in particular through the French Grand Est or the Camargue, some being potentially infected by the West Nile and Usutu viruses.
The tiger mosquito, which feeds on the blood of birds, then of humans, would therefore be an intermediate vector of transmission from birds to humans.
But then, how might these birds present in France transmit the viruses to Reunion, more than 10,000 kilometers away?
“The avifauna (wild and domestic) – which designates a set of bird species in a given region – is the natural reservoir of the West Nile and Usutu viruses”, explains the director of the IRD. “These viruses circulate in Europe, particularly around the Mediterranean, such as in the Camargue. Human cases of these two viruses have also been documented in Europe.”
He specifies, “the West Nile virus circulates periodically in Madagascar in the avifauna and human cases have also been documented in this large island”, which drastically reduces the kilometers which separate Reunion from this virus. “In 2016, published work from my laboratory had detected by serology traces of passage of the West Nile and Usutu viruses in seabirds on the scattered islands”, adds Patrick Mavingui.
A presence not far from our island which does not therefore exclude an introduction of these two viruses transmitted by the tiger mosquito to Reunion.
– A risk to be controlled –
If this risk is confirmed by the IRD, how can it be controlled? “Given the absence of a human vaccine once morest these two viruses (there is an equine vaccine once morest West Nile), control necessarily involves avoiding the introduction of these viruses when possible”, indicates Patrick Mavingui.
“Sustainable vector control, individual and community protection”, are also the main means.
Several schemes already exist in Reunion:
– ARS-LAV: entomological monitoring of vectors. All mosquito populations are monitored to find out which mosquitoes are present and where they are present on the Island.
– Hospitals, Public Health France, ARS: surveillance of human cases
– DAAF, CIRAD, veterinarians: surveillance of equine cases
– DEAL, OFB, SEOR: avifauna monitoring
– DP One Health Indian Ocean: research/teaching in human and animal health
Note that the fact that the Aedes albopictus mosquito is able to transmit these viruses does not change the level of risk
While the West Nile virus is not accompanied by any symptoms in most cases, it can cause, in regarding 20% of cases, a sudden fever, headache, muscle aches, sometimes associated with neurological complications ( meningitis, encephalitis) potentially severe. In less than 1% of cases, it can lead to other complications such as hepatitis, pancreatitis or myocarditis.
With regard to the Usutu virus, the main risk is that of Japanese encephalitis which results in central nervous disorders. The symptoms that should then alert are possible disorientation, loss of motor coordination, sudden weight loss, hepatomegaly (increase in the volume of the liver) or even splenomegaly (increase in the volume of the spleen).
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