Molecular characterization of isolated infectious bronchitis viruses from affected vaccinated broiler flocks in Syria

Tamara Al-Jallad,Fahim Abdelaziz,Mouhamad Al-Masalma,Morshed Kassouha,Mohamad Salhab,Anouar Alomar

doi:10.1186/s12917-020-02672-1

Abstract

BackgroundAvian Infectious Bronchitis Virus (IBV) is a highly contagious disease that imposes a huge economic burden on the global poultry industry. IBV contains numerous serotypes and variants with incomplete tenuous cross immunological protection. The failure of currently used vaccines to protect against diverse, circulating IBV strains that are specific to a given region poses a major problem for the poultry industry. Thus, there is an urgent need to conduct studies aimed at genotyping field IB viruses. In this study, we have determined the molecular characteristics of circulating IBV by sequencing the S1 gene of viral isolates from affected previously vaccinated broiler flocks suffering from the disease.ResultsTen isolates propagated in embryonated eggs showed an ability to induce typical IBV lesions after three successive viral passages. We performed a nested RT–PCR assay that targeted the hypervariable region 3 (HVR-3) of the S1 gene, and identified the isolates as IBV through sequence analysis. The IBV isolates showed sequence similarity between the Syrian isolates that vary from 96.20 to 100%, and those being closer to the Variant-2 strain IS/1494/06 (EU780077.2) with 97.5 to 99.4% similarities. However, less nucleotide identity was found with sequences belonging to the used vaccine strains such as H120, Mass5, and 4/91.ConclusionsThis study showed the presence of the Variant-2 strain circulating in Syrian broiler flocks showing signs of IBV disease. Currently, there is no commercial effective vaccine which protects birds against the Variant-2 strain. Continuous monitoring procedures should be taken to control and limit the spread of the IBV Variant-2 strain. This research emphasizes both the importance of epidemiological monitoring in intensive poultry farming for novel pathogens and the use of local isolates as future vaccine targets.

Highlights

Avian Infectious Bronchitis Virus (IBV) is a highly contagious disease that imposes a huge economic burden on the global poultry industry
After the third viral passage, typical IBV hemorrhagic embryonic lesions and delay of development and growth were observed in all eggs
Nested Reverse transcription (RT)-Polymerase Chain Reaction (PCR) Ten tissue samples were collected from the trachea (N = 7) or kidney (N = 3) of chickens suspected to have IBV

Summary

Introduction

Avian Infectious Bronchitis Virus (IBV) is a highly contagious disease that imposes a huge economic burden on the global poultry industry. We have determined the molecular characteristics of circulating IBV by sequencing the S1 gene of viral isolates from affected previously vaccinated broiler flocks suffering from the disease. The virus is acquired following inhalation or direct contact with contaminated poultry, litter, animal husbandry equipment, or other fomites [7]. It mainly affects the respiratory tract, the kidney, and the reproductive system of chickens across all age groups [2]. Chickens infected with IBV have decreased egg production and quality as a result of thin, fragile, misshapen shells, and thin watery eggs [5, 10]

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