Análise da evolução de uma variante do coronavírus aviário após infecção e persistência em matrizes de produção
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Data
2017-03-13
Autores
Fernando, Filipe Santos [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A bronquite infecciosa (BI) é uma doença altamente contagiosa que acomete o trato respiratório e urogenital de aves comerciais e que é causada pelo vírus da bronquite infecciosa (VBI) resultando em grandes perdas econômicas para a indústria avícola em todo o mundo. No presente estudo, foram obtidos três isolados de VBI de um lote matrizes de produção rotineiramente vacinado contra BI, em três diferentes idades, sendo que essas aves revelaram-se persistentemente infectadas com o VBI pelo período de 65 semanas em que foram avaliadas. Para tanto, foi realizada para esses três isolados do VBI uma análise molecular e filogenética da região S1 do gene que codifica a glicoproteína da espícula (S) e também foram caracterizadas a antigenicidade, a virulência e o tropismo tecidual através da infecção experimental em pintos livres de patógenos específicos (SPF) e de aves sentinelas, que foram colocadas em contato com as aves experimentalmente infectadas para avaliar o potencial de disseminação destes isolados de VBI. Os resultados revelaram que os três isolados do VBI são geneticamente próximos e sorologicamente relacionados, sendo classificados após a análise filogenética na linhagem 11 do genótipo I (GI-11), anteriormente denominada de genótipo BR-I, além de que esses vírus demonstraram maior tropismo e lesões renais. Foram observadas poucas diferenças em relação à patogenicidade para a traquéia e rins, que podem estar associadas a mutações que ocorreram no gene S1 destes isolados durante o período da infecção persistente. Os três isolados do VBI de aves pertencentes a um lote persistentemente infectado de matrizes de frangos de corte conservaram sua capacidade de infectar aves sentinelas por contato e causaram nessas aves alterações clínicas e patológicas semelhantes. Em conclusão, os isolados de IBV do genótipo I do BR estão evoluindo continuamente durante o ciclo produtivo de matrizes frangos de corte persistentemente infectadas, causando surtos episódicos da infecção que não são impedidos pelo atual programa de vacinação com as estirpes vacinais do genótipo / sorotipo Massachusetts. Além disso, as alterações genéticas no gene S1 destes isolados não foram capazes de alterar o seu tropismo e patogenicidade tecidual, mas parecem influenciar negativamente a eficácia das respostas imunes do hospedeiro contra estes vírus e favorecer a persistência viral.
Infectious bronchitis (IB) is a highly contagious disease that affects the respiratory and urogenital tract of commercial birds and is caused by infectious bronchitis virus (IBV), resulting in major economic losses to the poultry industry worldwide. In the present study, three isolates of VBI were obtained at three different ages from one set of broiler breeders that were vaccinated against IBV according to a routine protocol, and was persistently infected with IBV for the 65 weeks. A molecular and phylogenetic analysis of the S1 region of the gene coding for the spike glycoprotein (S) was performed for these three isolates. In addition, antigenicity, virulence and tissue tropism were also characterized by experimental infection of specific pathogen free chicks (SPF) and sentinel birds, which were used to assess the potential for dissemination of these IBV isolates. The results showed that the three IBV isolates are genetically and serologically close related, and after phylogenetic analysis they were classified in the BR-I genotype. In addition, these viruses demonstrated greater tropism and lesions for kidneys. There were few differences in pathogenicity for tracheal and renal tissues of experimental infected birds, and these differences may be associated with mutations that occurred in the S1 gene of these isolates during persistent infection. The three IBV isolates from persistently infected broiler breeders retained their ability to infect sentinel birds by contact and caused similar clinical and pathological changes in these birds. In conclusion, IBV isolates of BR genotype I are continuously evolving during the productive cycle of persistent infected broiler breeders, causing outbreaks that are not impeded by the current vaccination program with Massachusetts vaccine strains. In addition, the genetic alterations in the S1 gene of these isolates were not able to alter their tropism and tissue pathogenicity, but appeared to negatively influence the efficacy of host immune responses against these viruses and favor viral persistence.
Infectious bronchitis (IB) is a highly contagious disease that affects the respiratory and urogenital tract of commercial birds and is caused by infectious bronchitis virus (IBV), resulting in major economic losses to the poultry industry worldwide. In the present study, three isolates of VBI were obtained at three different ages from one set of broiler breeders that were vaccinated against IBV according to a routine protocol, and was persistently infected with IBV for the 65 weeks. A molecular and phylogenetic analysis of the S1 region of the gene coding for the spike glycoprotein (S) was performed for these three isolates. In addition, antigenicity, virulence and tissue tropism were also characterized by experimental infection of specific pathogen free chicks (SPF) and sentinel birds, which were used to assess the potential for dissemination of these IBV isolates. The results showed that the three IBV isolates are genetically and serologically close related, and after phylogenetic analysis they were classified in the BR-I genotype. In addition, these viruses demonstrated greater tropism and lesions for kidneys. There were few differences in pathogenicity for tracheal and renal tissues of experimental infected birds, and these differences may be associated with mutations that occurred in the S1 gene of these isolates during persistent infection. The three IBV isolates from persistently infected broiler breeders retained their ability to infect sentinel birds by contact and caused similar clinical and pathological changes in these birds. In conclusion, IBV isolates of BR genotype I are continuously evolving during the productive cycle of persistent infected broiler breeders, causing outbreaks that are not impeded by the current vaccination program with Massachusetts vaccine strains. In addition, the genetic alterations in the S1 gene of these isolates were not able to alter their tropism and tissue pathogenicity, but appeared to negatively influence the efficacy of host immune responses against these viruses and favor viral persistence.
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Palavras-chave
Galinha, Genótipo brasileiro, Patogenicidade, Persistência, VBI