Continuous clinicopathological and molecular recognition of very virulent infectious bursal disease virus in commercial broiler chickens

Abstract

Gumboro virus is one of the most dangerous immunosuppressant viruses that infect chickens and causes massive financial losses around the world. The purpose of the current study is to conduct a molecular survey of chicken farms for the infectious bursal disease virus (IBDV). On the basis of postmortem (PM) lesions, 125 bursal samples from 25 farms were collected from clinically diseased commercial chicken farms with increased mortality and suspected Gumboro virus infection. Pooled bursal samples from suspected IBD-vaccinated flocks were tested for IBDV by real-time polymerase chain reaction (RT-PCR). Fifteen out of 25 pooled specimens were found positive for IBDV, with a 60% detection rate, and confirmed positive for very virulent IBDV (vvIBDV). Nucleotide phylogenetic analysis of VP1 and VP2 genes was employed to compare the five chosen isolates with strains identified in various localities in 2022. The VP1 and VP2 genes are allotted into groups (I, II). The strains in our study were related to group II and it acquired a new mutation in the VP2 gene that clustered it into new subgroup B. By mutation analysis, the VP2 gene of all strains had a characteristic mutation to vvIBDV. It acquired new mutations in HVRs contrasted with HK64 in Y220F, A222T/V in all strains in our study, and Q221K that was found in IBD-EGY-AH5 and AH2 in the major hydrophilic region peak A in the loop PBC in addition to G254S in all strains in our study and Q249k that found in IBD-EGY-AH1 and AH3 in the minor hydrophilic region 1 in the loop PDE. These mutations are important in the virulency and antigenicity of the virus. The VP1 had 242E and 390L were characteristic of vvIBDV and KpnI restriction enzyme (777GGTAC/C782) in addition to a new mutation (F243Y and N383H) in tIBD-EGY-AH1 and AH4 strains. According to the current study, the strains were distinct from the vaccinal strain; they could be responsible for the most recent IBDV outbreaks observed in flocks instead of received vaccinations. The current study highlighted the importance of regular IBD monitoring to maintain up to date on the type of challenge viruses and the efficacy of commercial vaccinations.