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Usutu virus (USUV) is an emerging arbovirus that was first isolated in South Africa in 1959. This Flavivirus is maintained in the environment through a typical enzootic cycle involving mosquitoes and birds. USUV has spread to a large part of the European continent over the two decades mainly leading to substantial avian mortalities with a significant recrudescence of bird infections recorded throughout Europe within the few last years. USUV infection in humans is considered to be most often asymptomatic or to cause mild clinical signs. Nonetheless, a few cases of neurological complications such as encephalitis or meningoencephalitis have been reported. USUV and West Nile virus (WNV) share many features, like a close phylogenetic relatedness and a similar ecology, with co-circulation frequently observed in nature. However, USUV has been much less studied and in-depth comparisons of the biology of these viruses are yet rare. In this review, we discuss the main body of knowledge regarding USUV and compare it with the literature on WNV, addressing in particular virological and clinical aspects, and pointing data gaps.

National audience; Usutu virus (USUV) is an emerging arbovirus, close to the West Nile virus (WNV), which was first isolated in South Africa in 1959. This flavivirus has spread to a large part of the European continent, causing bird deaths, particularly in 2018. Although human infection seems to be mostly asymptomatic, several cases of neurological complications (encephalitis, meningoencephalitis) have been described. The description in Montpellier of an atypical case of Bell's palsy suggests that the clinical spectrum of USUV-related infections may be more extensive than expected and highlights our limited knowledge of the pathophysiology of this emerging virus.; Le virus Usutu (USUV) est un arbovirus émergent, proche du virus West Nile (WNV), isolé pour la première fois en Afrique du Sud en 1959. Ce flavivirus s’est propagé sur une grande partie du continent européen, provoquant des mortalités aviaires importantes, notamment en 2018. Même si l’infection humaine semble le plus souvent asymptomatique, plusieurs cas de complications neurologiques (encéphalites, méningoencéphalites) ont été décrits. La description à Montpellier d’un cas atypique de paralysie faciale a frigore suggère que le spectre clinique des infections liées à l’USUV pourrait être plus étendu qu’attendu et met en lumière nos faibles connaissances concernant la physiopathologie de ce virus émergent.

Le virus Usutu (USUV) est un arbovirus émergent, proche du virus West Nile (WNV), isolé pour la première fois en Afrique du Sud en 1959. Ce flavivirus s'est propagé sur une grande partie du continent européen, provoquant des mortalités aviaires importantes, notamment en 2018. Même si l'infection humaine semble le plus souvent asymptomatique, plusieurs cas de complications neurologiques (encéphalites, méningoencéphalites) ont été décrits. La description à Montpellier d'un cas atypique de paralysie faciale a frigore suggère que le spectre clinique des infections liées à l'USUV pourrait être plus étendu qu'attendu et met en lumière nos faibles connaissances concernant la physiopathologie de ce virus émergent.