West Nile and Usutu Virus Circulation in Wild Birds and Equids in Piedmont, Liguria and Aosta Valley, Northwestern Italy, in 2018-2020

Abstract

Purpose: A mandatory plan on West Nile (WNV) and Usutu (USUV), aimed at an early detection of viral circulation, is implemented in Italy through an active and passive monitoring. Here we report data on WNV and USUV circulation from 2018 till 2020 in birds and equids in three Northwestern regions of Italy (Piedmont, Liguria and Aosta Valley). Methods & Materials: Passive surveillance was carried out on wild birds found dead and as syndromic surveillance on neurological cases in equids. Active surveillance was performed on culled wild birds of target species (magpie, grey crow, jay). For each bird sampled, central nervous system and a pool of organs (heart, spleen and kidney) were analysed. For equids, analysis was carried out on blood samples and target organs (mainly spleen and central nervous system), from live and dead subjects, respectively. Viral RNA was extracted and purified using commercial kits and then assayed by real-time RT-PCRs detecting WNV Lineage 1 and 2, and USUV. All positive samples were sent to the OIE National reference Centre in Teramo (IZSTe) for confirmation. Results: From January 2018 to December 2020 a total of 4602 animals were analysed by RT-PCR, of which 172 equids and 4430 wild birds. The formers ones comprised 124 samples in 2018, 29 in 2019 and 19 in 2020 while 1201 samples were collected from wild birds in 2018, 1492 in 2019 and 1737 in 2020, respectively. Among equids, 12 tested positive to WNV in 2018 while no positivities were found in 2019-2020. Among avifauna, 32 subjects tested positive to WNV in 2018, 37 in 2019 and 41 in 2020 while 4 subjects resulted infected by USUV in 2018, none in 2019 and 2 ones in 2020. Positivities were found exclusively in samples from Piedmont and Liguria regions. WNV positive samples were all attributable to Lineage 2. Conclusion: Surveillance on WNV and USUV allowed to detect viral circulation in birds and equids in Northwestern Italy (Piedmont and Liguria regions) in 2018-2020, aimed at reducing human risk of infection, mainly through a timely enforcement of blood donors screening.