Usutu Virus

are important pathogens for humans and/or animals [9, 12]. Contrary to other representatives of flaviviridae such as WNV, yellow fever virus (YFV), and dengue virus (DENV), there are currently no comprehensive studies on the properties and replication of USUV. Based on the genome structure, however, it can be assumed that the virus behaves similarly to other flaviviruses such as WNV or DENV [9, 13]. Like other flaviviruses, the USUV particle is enveloped, with the envelope being derived from membranes of the host cell. The virus envelope encapsulates the virus capsid that contains the positive-strand RNA genome with a length of around 11,000 nucleotides. Sequence analyses of USUV isolates have shown that, as in all other flaviviruses, the genome encodes a single polyprotein with a size of around 3,400 amino acids, that is processed by cellular and viral proteases into structural and non-structural proteins. The first 3 genes encode the 3 proteins necessary for the structure of the virus: the capsid protein (C), the precursor membrane protein/membrane protein (prM/M), and the envelope protein (E). The right-hand part of the genome encodes 7 non-structural proteins with enzymatic activity and the regulatory proteins (fig. 1). The virus particle adheres to the host cell with its viral envelope protein E. The receptors on the cell responsible for adherence and uptake into the cell are unknown. Replication of the virus then occurs in the infected cell as described for other flaviviruses [9, 13].