Molecular epidemiology and evolution of avian infectious bronchitis virus

Abstract

Mutation and recombination processes are involved in the genetic and phenotypic variations of RNA viruses, leading to the emergence of new variant strains, and give rise to virus population diversity to be modeled by the host, particularly by the immune system, as occurred with infectious bronchitis virus (IBV) in chickens. The consequence is a continuous emergence of new IBV variants with regard to pathotypes, serotypes, and protectotypes. Nucleotide sequencing and subsequent genetic analysis of the S1 and N protein gene sequences provide a fast and accurate method to classify and predict IBV genotype, and a powerful instrument to monitor phylogenetic and epidemiological evolution of IBV variants. Despite the use of vaccination programmes, infectious bronchitis has become a serious problem in Brazil. Thus, a significant number of IBV field variants have been identified circulating in the Brazilian commercial poultries between 2000 to 2006 and more recently in Argentina. These viruses seem to be indigenous, because they demonstrated a low genetic relatedness with the majority of the reference strains from North America, Europe and Asia, but were moderately to highly related one to another. In summary, indigenous field IBV variants were evolving and circulating in the field in Brazil and Argentina, and should be considered as initial candidates for protection against current IBV infectious in chickens. However, in vitro and in vivo studies are needed to determine the pathogenicity and immunogenecity of these new isolates, before defining a new vaccine strain

Genotipificación de variantes del virus de bronquitis infecciosa aviar en el departamento del Tolima, Colombia

“…The GeneBank accession numbers of IBV variants are: IBV/Brazil/SC02 (GQ169247), IBV/Brazil/PR07 (GQ169244), I B V / B ra z i l / S P 0 2 ( G Q 1 6 9 2 5 0 ) , C u b a / L a inserción en la región S1 de la zona hipervariable (4). Otros países como Brasil, Argentina, Australia y Túnez, también pasan por la misma situación.…”

“…This control is not being effective because of the lack of cross-protection to the large number of variants and serotypes that are emerging. Studies using molecular methods have shown that the new strains or serotypes have only a few changes in amino acid in the S1 portion of the viral spike protein, while most of the genome remains unchanged (4,5). These changes may occur due to an immune pressure caused by widespread use of vaccines, genetic recombination or of coexistent infections, or even a dominant serotype reduction as a result of vaccination, allowing other emerging field strains (1,4,6,7).…”

“…Studies using molecular methods have shown that the new strains or serotypes have only a few changes in amino acid in the S1 portion of the viral spike protein, while most of the genome remains unchanged (4,5). These changes may occur due to an immune pressure caused by widespread use of vaccines, genetic recombination or of coexistent infections, or even a dominant serotype reduction as a result of vaccination, allowing other emerging field strains (1,4,6,7). The transmembrane domain is one of cleavage S1 region of the S virus structural protein, which is a hypervariable region, and the most antigenic and responsible for inducing protection against the virus (3).…”

“…In Colombia, vaccines with Massachusetts (Mass), Connecticut (Conn) e Arkansas strains are permitted to marketing (6), and even then, the disease is not being controlled, probably because the vaccine strain does not induce cross-protection to different genotypes that have emerged in the field with point mutations and deletion events insertion in the hypervariable region S1 (4). Other countries such as Brazil, Argentina, Australia and Tunisia also have the…”

“…Estudios con métodos moleculares han demostrado que las nuevas cepas o serotipos tienen solo pocos cambios en el aminoácido de la porción S1 de la proteína de la espícula viral, mientras que la mayor parte del genoma permanece sin cambios (4,5). Estos cambios pueden ocurrir debido a una presión inmune causada por el uso generalizado de vacunas, la recombinación genética, las infecciones coexistentes o incluso, una reducción del serotipo dominante como resultado de la vacunación, permitiendo la emergencia de otras cepas de campo (1,4,6,7). El dominio transmembrana es una región S1 de escisión de la proteína estructural de la espícula S, que es una región hipervariable, más antígena y responsable de inducir protección contra el virus (3).…”