Risk factors and genetic characterization of bovine respiratory syncytial virus in the inner Aegean Region, Turkey.

Bovine respiratory syncytial virus (BRSV) is one of the causative viral agents of the bovine respiratory disease complex. This study was conducted to determine the seropositivity and risk factors associated with BRSV infection and to evaluate the phylogenetic relatedness of the BRSVs in the inner Aegean region of Turkey. In this cross-sectional study, serum samples (n = 557) and nasal swabs (n = 21) were collected from cattle herds (n = 43) between February 2018 and March 2019. A commercial indirect-ELISA kit was used for the detection of antibodies in the sera samples. Reverse-transcriptase PCR was used to detect viral RNA in nasal swabs. Nasal samples were also examined for the detection of bovine parainfluenza-3, bovine viral diarrhoea virus, and bovine herpesvirus 1 by molecular detection methods. Genetic characterization of the local BRSV field isolates was conducted by sequencing attachment glycoprotein (G) gene segment. Epidemiological data on potential risk factors were collected from each sampled herd during blood collection. All herds had at least one seropositive animal. After adjustment for assay sensitivity and specificity, the overall true seropositivity was 58.48% (95% CI: 53.32-63.47). BRSV RNA was detected in 2 of the 21 nasal swabs, whereas other infectious agents were not detected in the investigated samples. Phylogenetic analysis showed that the field isolates of BRSV obtained in this study belonged to subgroup III, but they were located on separate branch from previously characterised Turkish subgroup III isolates. BRSV field strains from this study displayed 3 new amino acid substitutions (P89S, D115G, and S165L) in the G protein chains compared to other main reference BRSV isolates, demonstrating that BRSV is still evolving. Generalised estimating equation model showed that there were positive associations between BRSV infection, age (OR = 2.36, p = 0.001), herd size (OR = 10.32, p < 0.001), herd type (OR = 8.97, p < 0.001), a past history of respiratory disease (OR = 4.06, p < 0.001). The results of this study revealed that BRSV infection is common among cattle herds in the inner Aegean region of Turkey. The obtained epidemiological and genetic data on BRSV infection from this study could be beneficial for designing effective biosecurity practices and vaccination strategies.