Pathogenicity studies of the brazilian variant strain (BR) of infectious bronchitis virus

Author(s)

Leonardo Cardia Caserta

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2015-06-16

Examining board members

Clarice Weis Arns; Marco Aurélio Ramirez Vinolo; Luciano Kleber de Souza Luna

• Advisor: Helena Lage Ferreira; Clarice Weis Arns

Abstract

Recent studies identified variants of the Infectious bronchitis vírus (IBV) exclusives from Brazil (BR), which genotype is not related to the Massachussets serotype. In Brazil, alive vaccines for IBV are only allowed if belonging to this serotype, what suggests an inefficient protection against brazilian variants. Due to the lack of studies focusing the pathogenicity of the BR variant of IBV, the knowledge of its effects become necessary, elucidating clinical signs, macroscopic and microscopic lesions, besides the immunity against this virus. This study aims to analyse the pathogenicity and tropism of the BR variant of IBV for poultries through a in vivo experiment, using day old specific pathogen free (SPF) chicks. Previously, 12 serial passages in embryonated eggs were performed with the aim to increase the viral load and to perform the titration of strains 801 ans 810, reaching the expected effects on the embryos (curling, dwarfing and hemorrhage). The viral titre obtained was around 105 EID. When inoculated in the chicks, produced respiratory clinical signs and macroscopic lesions in kidneys and trachea. In the ciliary activity test, tracheal fragments were collected and examined. A ciliary activity inhibition was observed between 7 and 9 d.p.i. (days post inoculation). The results obtained using the qRT-PCR technique showed the respiratory organs as a primary replication site, in consonance with the clinical signs observed in the first days of experiment. The highest RNA levels were detected in the digestory system, where the persistence was also the longest. Nevertheless, the histopathological examination confirmed the findings of others studies, that showed only a few microscopic lesions, despite the high RNA level detected. In the respiratory system, however, microscopic lesions were consistent with clinical signs and RNA detection. Both groups presented a low antibody response. With the results of this study, it is possible to conclude that these brazilian varianst presented a pathogenicity very similar to the Massachusetts strains, with respiratoty tropism and are also able to replicate in large quantitites in the digestory and urinary system, but causing only a few or no lesions (AU)

• FAPESP's process: 13/02058-6 - Pathogenicity studies of the Brazilian variant strain (BR) of infectious bronchitis virus
• Grantee: Leonardo Cardia Caserta
• Support Opportunities: Scholarships in Brazil - Master