Risk assessment of the Usutu virus

The Usutu virus (USUV) belongs to the Flaviviridae family and was first isolated in 1959 from mosquitoes near the Usutu River (present-day Kingdom of Eswatini). Like other flaviviruses, USUV is approximately 40–60 nm in size, enveloped, and possesses a single-stranded RNA genome of approximately 12 kb with positive orientation. Following its discovery, the virus was detected in various African animals (mosquitoes, birds, horses, dogs, and rodents). In Europe, USUV proved to be highly pathogenic for various bird species, particularly blackbirds (Turdus merula) and great grey owls (Strix nebulosa). By 2018, USUV infections in birds had been recorded in 16 European countries, including Germany. The viruses are transmitted to birds via mosquitoes. Since 2009, USUV has occasionally been detected in both immunocompromised and immunocompetent humans, but only in a few cases has it manifested as neuroinvasive disease or USUV fever. In TRBA 462 "Classification of Viruses in Risk Groups," USUV is assigned to Risk Group 2 and designated as a zoonotic pathogen. Furthermore, TRBA 462, Note 1, points out that additional precautions must be taken when handling USUV when working with arthropods (natural vectors) and/or in animal experiments. According to Section 5 (1) of the GenTSV in conjunction with the criteria in Annex I of the GenTSV, the ZKBS (Ref. 45242.0184) classifies USUV as a donor and recipient organism for genetic engineering work in Risk Group 2 , as the virus is highly pathogenic for native birds and has zoonotic potential. In immunocompetent individuals, however, USUV rarely causes symptoms, which are usually mild.