Effects of chicken anaemia virus and infectious bursal disease virus-induced immunodeficiency on infectious bronchitis virus replication and genotypic drift

Abstract

We followed changes in a portion of the S1 gene sequence of the dominant populations of an infectious bronchitis virus (IBV) Arkansas (Ark) vaccine strain during serial passage in chickens infected with the immunosuppressive chicken anaemia virus (CAV) and/or infectious bursal disease virus (IBDV) as well as in immunocompetent chickens. The IBV-Ark vaccine was applied ocularly and tears were collected from infected chickens for subsequent ocular inoculation in later passages. The experiment was performed twice. In both experiments the dominant S1 genotype of the vaccine strain was rapidly and negatively selected in all chicken groups (CAV, IBDV, CAV'IBDV and immunocompetent). Based on the S1 genotype, the same IBV subpopulations previously reported in immunocompetent chickens and named component (C) 1 to C5 emerged both in immunocompetent and immunodeficient chickens. During the first passage different subpopulations emerged, followed by the establishment of one or two predominant populations after further passages. Only when the subpopulation designated C2 became established in either CAV-infected or IBDVinfected chickens was IBV maintained for more than four passages. These results indicate that selection does not cease in immunodeficient chickens and that phenotype C2 may show a distinct adaptation to this environment. Subpopulations C1 or C4 initially became established in immunocompetent birds but became extinct after only a few succeeding passages. A similar result was observed in chickens co-infected with CAV 'IBDV. These results suggest that the generation of genetic diversity in IBV is constrained. This finding constitutes further evidence for phenotypic drift occurring mainly as a result of selection.

Analysis of antigenicity and pathogenicity reveals major differences among QX-like infectious bronchitis viruses and other serotypes

“…The pathogenicity test indicated that inoculation of SPF chickens with the SD strain resulted in clinical signs consistent with an IB-like disease, and respiratory signs in the birds were most apparent. The mortality rate of the SD strain was higher (reaching 67%) than that reported previously (Gallardo et al, 2012) suggesting it is a highly pathogenic strain. The SD strain caused obviously swollen and pale kidneys, with ureters distended with urate.…”

Gonadal pathogenicity of an infectious bronchitis virus strain from the Massachusetts genotype

“…These changes in tissue tropism could be a consequence of escaping mechanisms of the virus associated with the immune pressures driven by vaccination protocols for IBV [39,40]. Furthermore, it has been demonstrated that immunity is not the only selective pressure on IBV [41] and the genetic diversity in viral isolates is attributed to shifts in population equilibrium of the replicating viral genomes even in the absence of immune selection pressure [42]. Such divergence between genotype and predominant pathotype or tissue tropism has also been reported in an IBV isolate from Egypt (Egypt/F/ 03), which, despite being classified as Massachusetts, showed a marked nephropathogenicity in experimentally infected SPF chickens [43].…”

Variability Assessment of California Infectious Bronchitis Virus Variants

“…The sequence of the first 753 nucleotides of the S1 coding sequence was obtained. This sequence, containing the hypervariable region of the IBV S1 gene, has been repeatedly used to demonstrate IBV genetic diversity (7,8,9). Sequences were assembled and aligned by using the MacVector 12.7 software (MacVector Inc., Cary, NC).…”