Reversion of molecularly engineered, partially attenuated, very virulent infectious bursal disease virus during infection of commercial chickens

Abstract

A molecularly cloned, tissue culture-adapted infectious bursal disease virus (BD-3tc) was generated from a very virulent strain by the reverse genetics approach following site-directed mutagenesis (Q253H and A284T in VP2). The pathogenicity of BD-3tc was tested in commercial chickens. The wild-type strain (BD-3wt) and the molecularly cloned parental strain (BD-3mc) were included for comparison. The subclinical course of the disease, with delayed and milder pathological lesions followed by quick follicular regeneration in the bursa of Fabricius in BD-3tc-inoculated birds, suggested that these amino acid substitutions made BD-3tc partially attenuated. However, severe bursa atrophy was observed at 14 days after inoculation. Reverse transcription-polymerase chain reaction coupled with restriction enzyme analysis revealed that both point mutations in BD-3tc had reverted 14 days after inoculation. Further investigations demonstrated that the codon for amino acid at position 284 had already reverted to the wild-type phenotype (T284A) 3 days after inoculation.

Both Genome Segments Contribute to the Pathogenicity of Very Virulent Infectious Bursal Disease Virus

“…In addition, the alteration of VP2 amino acids (aa) 253, 279, and/or 284 of a vvIBDV strain by reverse genetics conferred adaptation to chicken embryo fibroblasts (CEF) (32)(33)(34). The resulting viruses proved to be attenuated for chickens (34,35), but reversion mutations were observed upon passage in chickens and could restore virulence (36). VP2 is, however, unlikely to be the only factor for virulence: laboratory-engineered reassortant viruses derived from vvIBDV exhibited delayed replication in the bursa (37) or failed to induce morbidity and mortality (31) unless they also had a typical vvIBDV-related segment B.…”

Three Amino Acid Mutations (F51L, T59A, and S390L) in the Capsid Protein of the Hepatitis E Virus Collectively Contribute to Virus Attenuation

“…Single point mutations in the capsids of poliovirus (65), murine norovirus (4), infectious bursal disease virus (64), and adenoassociated viruses (67) have all been demonstrated to have significant effects on both in vitro and in vivo growth characteristics of the viruses. Reversion of an attenuated phenotype to a pathogenic wild type has also been reported for many animal viruses, such as poliovirus (35), porcine reproductive and respiratory syndrome virus (48), and infectious bursal disease virus (54). In the current study, the F51L and T59A mutants are genetically stable in pigs, as the viruses recovered from the inoculated pigs over the course of infection all retained these two mutations.…”

Effect of Mentofin and ASI-MIRUS on Humoral Immune Response and Tissue Changes in Infectious Bursal Disease Vaccinated Broiler Birds

“…Tissue samples were embedded in paraffin and were stained through hematoxylin and eosin (Bancroft and Gamble, 2008). Bursal lesions like lymphocytic depletion and other histological changes in bursa of Fabricious were scored (Raue et al, 2004). Lymphocytic depletion and bursal damage were scored according to following criteria: 0=Normal lymphoid follicles, 1=Mild depletion of lymphoid follicles shown by thinning of lymphocyte population without focal necrosis or notable edema, 2=Moderate depletion of lymphoid follicles accompanied by interfollicular edema and focal necrosis, 3=Severe depletion of lymphoid follicles having no lymphocyte but only reticular cell, and 4=Atrophy of follicles commonly with cystic spaces, in folding of epithelium and clear fibroplasias.…”