Survey of flaviviruses on long- and short-distance migratory birds in Trentino Alto-Adige (North-eastern Italy) with oral and cloacal swabs

Background West Nile virus (WNV) and Usutu virus (USUV) (genus Flavivirus, Flaviviridae family), are emerging as important pathogens. They are maintained in nature by a cycle involving ornithophilic mosquitoes, principally Culex spp., and birds. Migratory birds are involved in the spread of Flaviviruses over long distances, particularly from Africa to Europe. There is still a knowledge gap on the role played by the different bird species in the ecology and transmission mechanisms of these viruses. Trentino-Alto Adige (North-eastern Italy) is located on the migratory route of many of the short- and long-distance migratory birds that cross the Alps. Until now, only a silent circulation of WNV and USUV within this territory has been confirmed by serological screenings. Continuous spillover events of both viruses, however, have been reported in the neighbouring regions. The aim of this study was to detect if active virus shedding occurs in migratory birds captured during their seasonal movements. Methods Oral and fecal swabs' collection was carried out in Trentino-Alto Adige region during the 2011 and 2012 autumnal ringing campaigns and during the 2012 spring ringing campaign. Samples belonging to 18 transaharian and 21 intrapaleartic species were tested during spring (n=176) and autumn (n=146) using a generic nested-PCR for Flaviviruses. Results All samples tested negative. Discussion Flaviviruses transmission dynamics is based on a complex relationship between virus, host, vector species, environmental and climatic factors. In previous studies, the oro-fecal shedding has been found only in some of the bird species. Our results further corroborate the results of a previous study carried out in Italy, which found there was no evident oro-faecal shedding of USUV and WNV in the families Fringillidae, Lanidae, Paridae, Muscicapidae, Silvidae, Turdidae, Hirundinidae and Picidae. Our results also seem to suggest that families Motacillidae, Prunellidae, Emberizidae, Cuculidae, Egitalidae, Strigidae may not be important shedders. The lack of detection of active virus shedding does not exclude the circulation of these viruses within this region. Their circulation is anyway apparently very limited. Many factors can be involved: the lenght of the shedding with regard to the lenght of the migratory movements, the low density of mosquitoes, the lack of suitable habitat for Culex spp., the mountainous orography of the territory and the high avian biodiversity