Characterization of S1 gene sequence variations of attenuated QX-like and variant infectious bronchitis virus strains an
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ORIGINAL ARTICLE
Characterization of S1 gene sequence variations of attenuated QX‑like and variant infectious bronchitis virus strains and the pathogenicity of the viruses in specific‑pathogen‑free chickens Mohd Iswadi Ismail1,3 · Tan Sheau Wei1 · Mohd Hair‑Bejo1,2 · Abdul Rahman Omar1,2 Received: 6 May 2020 / Accepted: 13 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Besides the vaccine strains, the Malaysian variant (MV) and QX-like are the predominant IBVs detected on commercial poultry farms. These two virus strains are distinct based on genomic and pathogenicity studies. In this study, we determined the sequence of the S1 gene and compared the pathogenicity of serial passage 70 (P70) of Malaysian QX-like (QX/P70) and MV (MV/P70) strains with that of their respective wild-type viruses. The nucleotide and amino acid sequences of the complete S1 genes of QX/P70 and MV/P70 showed 1.4 to 1.6% and 3.0 to 3.3% variation, respectively, when compared to the wild-type virus. Most of the mutations were insertions and substitutions in the hypervariable regions (HVRs), primarily in HVR 3. Furthermore, selection pressure analysis showed that both viruses are under purifying selection. A pathogenicity study in specific-pathogen-free (SPF) chickens showed a reduction in respiratory and kidney lesions in chickens inoculated with MV/P70, but not with QX/P70, when compared to the respective wild-type viruses. However, MV/P70 is still pathogenic and can cause ciliary damage. In conclusion, the MV IBV strain is more responsive than the QX-like IBV strain following the attenuation process used for the development of a live attenuated IBV vaccine.
Introduction Avian infectious bronchitis virus (IBV) is the causative agent of infectious bronchitis (IB), a highly contagious disease of chickens that can cause severe economic losses to the poultry industry due to high morbidity and mortality, a decline in egg quality and quantity, and increased costs for medication, since infected chickens may succumb to secondary bacterial infection [1, 2]. IB is characterized by respiratory disease, but some strains can cause severe kidney damage and intestinal disease [3].
Handling Editor: John Ziebuhr. * Abdul Rahman Omar [email protected] 1
Institute of Bioscience, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
2
Faculty of Veterinary Medicine, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia
3
Department of Veterinary Services, Veterinary Research Institute, No. 59, Jalan Sultan Azlan Shah, 31400 Ipoh, Perak, Malaysia
IBV is a single-stranded, enveloped RNA virus that belongs to the genus Gammacoronavirus, family Coronaviridae, order Nidovirales [4]. The most prominent feature of IBV is the spike (S) glycoprotein, which projects from the surface of the virion [5]. The S protein has two subunits, S1 and S2, which plays a vital role in inducing immunity and in determining the virulence of the virus [6]. The S1 subunit is responsible for the attachment of the virus to cell
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