BRIEF REPORT Gene segment reassortment between Eurasian and American clades of avian influenza virus in Italy Alice Fusaro • Isabella Monne • Giovanni Cattoli • Roberta De Nardi • Annalisa Salviato • Ana Moreno Martin • Ilaria Capua • Calogero Terregino Received: 3 August 2009 / Accepted: 3 November 2009 / Published online: 19 November 2009 Ó Springer-Verlag 2009 Abstract All genes of avian influenza A viruses are phylogenetically distinguished into two large clades, namely the American and Eurasian clade. Reassortments among the gene segments of influenza viruses belonging to the two distinct clades are rare events and have never been described in poultry in Europe and Asia before. This study presents the genetic characterization of two influenza viruses isolated from domestic mallards in Italy in 2004 and 2005. Phylogenetic analysis of the entire genome showed that these viruses contain mixed gene segments belonging to the American and Eurasian clades. The genome of influenza A viruses consists of eight RNA segments of negative polarity that encode 11 proteins. At present, 16 haemagglutinin (HA) and 9 neuraminidase (NA) subtypes have been identified [1]. Wild aquatic birds are the natural reservoirs for influenza A viruses of all known HA and NA subtypes, and these viruses are occa- sionally transmitted to other species, including domestic poultry and mammals [2]. All genes of avian influenza A viruses are divided into two large phylogenetic clades: one containing viruses from the Americas, the other including viruses from Eurasia (Australia and Africa also included). Reassortment events within viruses belonging to the same large phylogenetic clade occur frequently [3, 4], while only few cases of reassortant viruses containing genes from both American and Eurasian clades have been reported [5, 6]. Based on the analysis of 6,767 influenza A gene segments, Krauss et al. [5] found a low frequency of inter-hemispheric gene transfer (\0.6%) and demonstrated that the rate of reas- sortment events varied according to gene segment, ranging from 0.25% for the M gene to 1.77% for the HA gene. Recently, Koehler et al. [7] observed higher frequency of Asian reassortment events (3.1%) among Alaska northern pintails, possibly due to the reduced distance from areas where Asian clades commonly circulate. Interestingly, an avian influenza genome entirely belonging to the Eurasian lineage (i.e. all eight gene segments) has not been reported in America, or vice versa [5–7]. At present, reassortant viruses containing genes from both phylogenetic clades have been detected in wild aquatic birds in Australia [8], Japan [9, 10], South Africa [11], North America [4, 12, 13], Alaska [7] and in the Bering Strait area [14]. In Europe, reports of reassortment events are limited to one virus collected in a guillemot (Uria aalge) in Sweden [15]. In February 2004 and in January 2005, during surveil- lance of backyard flocks in northern Italy, two low-patho- genic avian influenza viruses, A/duck/Italy/775/2004 (H5N3) and A/mallard/Italy/119/2005 (H11N9), were iso- lated from cloacal swabs collected in two domestic mal- lards (Anas platyrhynchos) of two distinct backyard flocks. Genetic characterization revealed that the M gene sequence of both viruses and the HA gene of the H11N9 isolate belong to the American clade. In this study, we generated data on genomic analysis of the two reassortant Italian viruses, thereby providing insights into possible ways of A. Fusaro (&) Á I. Monne Á G. Cattoli Á R. De Nardi Á A. Salviato Á I. Capua Á C. Terregino OIE/FAO and National Reference Laboratory for Newcastle Disease and Avian Influenza, Istituto Zooprofilattico Sperimentale delle Venezie, Viale dell’Universita` 10, 35020 Legnaro, Padova, Italy e-mail: afusaro@izsvenezie.it A. Moreno Martin Istituto Zooprofilattico Sperimentale della Lombardia ed Emilia Romagna, via A. Bianchi, 9, 25124 Brescia, Italy 123 Arch Virol (2010) 155:77–81 DOI 10.1007/s00705-009-0550-2