Introduction
Avian metapneumovirus (aMPV) infections in Europe have been an issue since its first appearance both in turkeys, chickens and in other minor species (Toquin, Bayon-Auboyer, Eterradossi, & Jestin, 1999; Catelli et al., 2001; Cecchinato, Ferreira, Munir, & Catelli, 2017; Cecchinato et al., 2018), causing economic losses mainly due to respiratory or reproductive problems (Cecchinato et al., 2012), often exacerbated by secondary bacterial infections (Giovanardi et al., 2014).
First aMPV isolations in Europe date back to the second half of the 1980s, when Turkey Rhinotracheitis (TRT) outbreaks appeared in the United Kingdom (McDougall and Cook, 1986) and France (Giraud, Bennejean, Guittet, & Toquin, 1986). As the virus was spreading all over Europe and the clinical problems in poultry farms became increasingly serious, during the early 1990s (Cook et al. 1989a e 1989b) live attenuated vaccines were developed and became commercially available. By analysing strains circulating in Europe, Juhasz and Easton (1994) reported differences in the G gene between aMPV isolates and proposed the classification into A and B subtypes and confirmed the co-circulation of both subtypes. After this initial study, and due to the increasing use of sequence analysis, two further subtypes, named C and D, were identified in France (Bayon-Auboyer, Arnauld, Toquin, & Eterradossi, 2000; Toquin et al., 2006).
Despite these reports, molecular data on aMPV strains circulating in Europe are still poor and scattered (Catelli et al., 2004; Cecchinato et al., 2013a; Listorti et al., 2014; Franzo et al., 2017; Tucciarone et al., 2017 a 2018; Ball, Forrester, & Ganapathy, 2018; Andreopoulou et al., 2019), as most of them originate from few countries. In the last decades, subtype B has been generally the most frequently encountered subtype in Europe, although subtype A has been sporadically reported (Lupini et al., 2011).
In order to update the epidemiological picture of circulating strains, the present study was designed to molecularly characterize, by partial G gene sequencing, aMPV subtype B strains detected in Europe in the last years.