West Nile Virus and Usutu Virus Co-Circulation in Europe: Epidemiology and Implications

Abstract

West Nile virus (WNV) and Usutu virus (USUV) are neurotropic mosquito-borne flaviviruses that may infect humans. Although WNV is much more widespread and plays a much larger role in human health, the two viruses are characterized by similar envelope antigens, clinical manifestations, and present overlapping in terms of geographic range of transmission, host, and vector species. This review highlights some of the most relevant aspects of WNV and USUV human infections in Europe, and the possible implications of their co-circulation.

Keywords: Usutu; West Nile; co-circulation; epidemiology.

Figure 1

Geographic distribution of WNV (green) and USUV (red) in Europe. Co-circulation, paired with antigenic similarity and overlapping clinical expression of the infections, complicates the diagnosis of febrile conditions, leading to suboptimal case management. More importantly, this may directly alter the epidemiology of these viruses. This was shown in California, after the introduction of WNV caused the displacement of Saint Louis encephalitis virus (SLEV), and in Thailand, with an increased severity of dengue virus (DENV) infection symptoms in individuals with previous JEV infection [86,87].