GI-16 lineage (624/I or Q1), there and back again: The history of one of the major threats for poultry farming of our era

Franzo, Giovanni; Cecchinato, Mattia; Tosi, Giovanni; Fiorentini, Laura; Faccin, Francesca; Tucciarone, Claudia Maria; Trogu, Tiziana; Barbieri, Ilaria; Massi, Paola; Moreno, Ana

Interestingly, although the migration rate was predicted to be low at the beginning of the GI-16 epizootiology (i.e. from Italy to China), the following steps were characterized by a much higher rate (Fig 5) , likely reflecting the dense commercial connections among countries and the limited efficacy of implemented biosecurity measures [23] . The virus introduction from Europe to China could be ascribable to live animal movements, in particular of breeders that were imported to improve and/or substitute the local genetic lines [40] . Additionally, it must be stressed that, even if the inferred link involved Italy and China, the GI-16 lineage was probably present before the 1990s (undetected, improperly characterized or unsequenced) in several European countries, which could have played a relevant role in the eastward viral spread. However, extremely poor data reporting live poultry import and export from China are present and most of the countries considered in the present study declare no trade flows with China [14, 18] . Therefore, other sources of viral spreading must be considered and the Phylodynamic analysis of IBV GI-16 lineage role of wild birds is often considered as a suggestive hypothesis. In fact, circulation of IBVrelated Gamma-coronaviruses in wild species, including migratory birds, has been reported, sometimes with high prevalence [41] [42] [43] . An involvement of these species in the spread of GI-16 can not be a priori excluded, especially over relatively short/medium distances (e.g within Europe and Asia or between these two regions) covered by recognized flyways. However, although the overlap between the East Asia/Australasia and East Asia/East Africa with the Pacific America and Central America flyways could explain the GI-16 introduction to South America, the extreme distance coupled with the absence of detection of this genotype in North America discount this hypothesis. Additionally, it must be stressed that GI-16 and other "wild type" genotypes have never been identified in wild birds and further studies will be necessary to properly and systematically investigate the role of wild birds in IBV epidemiology. In this background, other explanations like illegal or unreported animal trades appear more likely.