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

Abstract

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.

Molecular Characterisation and Antibody Response to Bovine Respiratory Syncytial Virus in Vaccinated and Infected Cattle in Turkey

“…Findings with PCR in other studies performed in Turkey have been both similar and different compared to those obtained in the present study [ 27 , 36 , 37 ]. In one previous study in Erzurum, Turkey, 1.29% of 155 nasal swabs were positive for BRSV-RNA [ 36 ].…”

“…The first study reported 46.12% seropositivity in non-vaccinated cattle [ 47 ]. Non-vaccinated cattle sera were analysed in another study in Turkey, which found seropositivity of 44.6% in Central Anatolia [ 48 ], 58.48% in Afyonkarahisar and Usak provinces [ 27 ], 67.3% in Eastern and Southeastern Anatolia [ 49 ], 73% in Marmara Region [ 50 ], 76.38% in Denizli and Burdur provinces [ 51 ], 97.1%in Adiyaman province [ 52 ], and 98.6% in Aydın province [ 51 ]. In neighboring countries, BRSV seroprevalence in non-vaccinated animals was found to be 83.11% in Iraq [ 53 ] and 51.1% [ 54 ] and 89.1% in two studies from Iran [ 55 ].…”

“…However, in a study performed in 2018 in Samsun, Turkey, three lugs were analysed and all samples were positive for BRSV-RNA [ 37 ]. In addition, 2 of 21 nasal swabs were positive for BRSV-RNA in Afyonkarahisar and Usak, representing a low level of BRSV circulation [ 27 ]. Higher detection rates were reported in the neighboring countries Iraq (37.31%) [ 53 ] and Iran (78.12%) [ 66 ].…”

“…BRSV Subgroup-II includes genotypes detected in northern European countries such as Denmark, Sweden, and Norway; some of the BRSV genotypes detected in Japan have been reported to belong to Subgroup-II as well [ 20 , 25 ]. BRSV Subgroup-III, including the strains detected in Turkey, mainly includes genotypes reported from the USA [ 20 , 26 , 27 ]. BRSV Subgroup-IV is divided into two subclasses, called IA and IB, as reported by Valarcher and colleagues [ 20 ].…”

“…BRSV has been isolated from many countries in Europe, America, Asia, and Africa including Turkey [ 31 , 32 , 33 , 34 , 35 ]. The majority of studies in Turkey have been aimed at determining the seroprevalence of BRSV among cattle herds, and there is limited knowledge available about sequence and phylogenetic analyses of BRSV [ 27 , 36 , 37 ]. The isolation of the virus using cell cultures is rather difficult; in addition, two samples separated by an interval of 2–3 weeks need to be taken for the antibody response to distinguish between infected and vaccinated animals.…”