Evaluating the pathogenicity of GI-23 genotype of Infectious Bronchitis Virus isolated in Egypt and assessment of the protective efficacy of the variant II vaccine against it

Document Type : Original Article

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Department of Virology, Faculty of Veterinary Medicine, Benha University, Egypt

Abstract

Infectious bronchitis virus (IBV) is a critical poultry pathogen that causes major economic losses globally. IBV has high levels of genetic, serotype, and pathotypic variability. In Egypt, the predominant genotype identified is GI-23 (Var II), which persists in its dissemination and pathogenic impact within the avian population, notwithstanding the enforcement of rigorous vaccination protocols. This study investigates the pathogenicity of the GI-23 genotype of IBV, specifically the strain isolated in Egypt (IBV/CH/EG/Moshtohor-3/2023), using one-day-old specific pathogen-free chicks. The chicks were inoculated with 105 EID50 of the virus in 0.1 mL via the intranasal route. Clinical signs, mortality rates, histopathological changes, and viral shedding were systematically monitored over 14 days following infection. Furthermore, it evaluates the protective efficacy of a commercially available variant II vaccine against this particular strain. The findings of this study revealed a considerable level of pathogenicity, as evidenced by a 40% mortality rate in infected SPF chicks, accompanied by severe respiratory and renal lesions, as well as elevated viral loads in oropharyngeal swabs. Furthermore, the variant II vaccination conferred a high protection rate of 93.4% and achieved a ciliostasis score of 0, indicating valuable protection against ciliary dysfunction.

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