Mosquito, bird and human surveillance of west nile and usutu viruses in Emilia-Romagna region (Italy) in 2010.

Background To evaluate the presence of West Nile (WNV) and Usutu (USUV) viruses a surveillance system, including mosquito- and bird-based surveillance, was established in the Emilia-Romagna region since 2008, after the first WNV detection in the region. Surveillance has been improved in subsequent years by enlarging monitored area and increasing number of mosquitoes birds tested. Methodology/Principal Findings A network of mosquito traps, evenly distributed and regularly activated, was set up within the surveyed area. A total of 438,558 mosquitoes, grouped in 3,111 pools, were tested by biomolecular analysis. Moreover, a total of 1,276 birds were tested, of which 1,130 were actively sampled while 146 originated from passive surveillance. The survey detected WNV in 3 Culex pipiens mosquito pools, and USUV in 89 Cx. pipiens pools and in 2 Aedes albopictus mosquito pools. Two birds were WNV-positive and 12 were USUV-positive. Furthermore 30 human cases of acute meningoencephalitis, possibly caused by WNV or USUV, were evaluated for both viruses, and 1,053 blood bags were tested for WNV, without any positive result. Conclusions/Significance Despite finding no symptomatic human WNV or USUV infections during 2010, the persistence of the viruses, probably due to their overwintering, was confirmed in the region through viral circulation in both mosquitoes and birds. In 2010, circulation of the two viruses was lower and started later in the season than in 2009, but this decrease was not explained by the relative abundance of Cx. pipiens which was greater in 2010. USUV detection in mosquito species confirms the role of Cx. pipiens as the main vector of the virus and the possible involvement of the Ae. albopictus in the USUV cycle.