First molecular characterisation of avian metapneumovirus (aMPV) in Turkish broiler flocks

Viral respiratory diseases including avian metapneumovirus (aMPV) have a significant economic impact on poultry industries. The frequency and genotype diversity of aMPV in Turkish broiler flocks is not known at present. The aim of this study was to report the first molecular identification and phylogeny of aMPV which is circulating in Turkish broiler flocks. Trachea tissue samples and tracheal swabs were collected from 110 broiler flocks distributed in different geographical regions in Turkey between March 2017 and March 2018. Detection of aMPV was confirmed using universal reverse transcriptase RT-PCR and 8 (7.2%) broiler farms were positive for aMPV. Sequence analysis of the G gene revealed the exclusive presence of subtype B viruses. Three field isolates clustered closely with a 2002 Israel isolate, indicating a potential transmission route between these two countries and through the Middle East. The remaining five field isolates were closely related to a vaccine strain even though broiler flocks in Turkey are not routinely vaccinated against aMPV. Therefore we speculate these five isolates could have originated from nearby vaccinated turkey farms. Additionally, the presence of some nucleotide substitutions compared to the reference vaccine sequence suggests prolonged circulation and evolution of the original vaccine virus or a vaccine subpopulation was selected under field conditions. This evidence emphasises the need for further detailed and more systemic approaches to evaluate aMPV spread and evolution in order to design effective control strategies.