Detection of Usutu Virus Within a West Nile Virus Surveillance Program in Northern Italy

Abstract Usutu virus (USUV) is a mosquito-borne flavivirus belonging to the Japanese encephalitis serocomplex, recently related to neurological disease in immunosuppressed patients. In the same area of Northern Italy where USUV human cases occurred in 2009, a regional West Nile virus (WNV) surveillance program based on mosquito monitoring and wild birds screening has been implemented since 2008. Mosquito pools and wild birds were tested using three different polymerase chain reactions (Flavivirus, WNV, and USUV). During summer 2009, 56 pools (54 consisting of Culex pipiens and 2 of Aedes albopictus) and 27 pools (Cx. pipiens) out of 1789 mosquito pools were, respectively, USUV and WNV positive. Moreover, out of 1218 wild birds tested, 44 were WNV positive, whereas only 11 birds were USUV positive by polymerase chain reaction. Data collected during 2009 prove a cocirculation of USUV and WNV in Northern Italy, but these two viruses show different incidence values in both mosquitoes and birds, suggesting inv...