The South African poultry industry has been beset by sporadic H6N2 avian influenza infection (sub-lineage I and II) in chickens since the early 2000s, with economic losses resulting from reduced egg production and co-infection with other pathogens. An egg-based inactivated H6N2 vaccine (AVIVAC® AI; Deltamune (Pty) Ltd.) based on a 2002 sub-lineage I isolate is available, although substantial antigenic drift has occurred in H6N2 viruses since its implementation. Globally, seasonal and pandemic plant-produced hemagglutinin (HA)- based influenza virus-like particle (VLP) vaccines are in advanced clinical trials with proven efficacy, speed of production, cost-effectiveness, scalability and safety, although not yet established for poultry. In this study, H6 avian influenza VLPs (sub-lineage I and II, respectively) were transiently produced in Nicotiana benthamiana and tested for protective efficacy in the target host. A production platform has been established for H6 VLPs in N. benthamiana by optimising protein expression and purification to maximize yield and by assessing the feasibility of large-scale production and downstream processing in a preliminary study. Subsequently, the respective plant-produced H6 VLPs were formulated into vaccines and their capacity to reduce viral replication and shedding upon challenge with a 2016 H6N2 field isolate were established in specific-pathogen-free (SPF) chickens, in comparison to the commercial H6N2 vaccine. The plant-produced sub-lineage I VLP vaccine (768 HA units/dose) was highly immunogenic (mean hemagglutination inhibition (HI) titer 10.7 log2), reduced the oropharyngeal and cloacal viral shedding by more than 100- and 6-fold, respectively, and shortened the duration of oropharyngeal shedding by at least a week in comparison to the non-vaccinated control. Due to initial low yield of sub-lineage II VLPs, the maximum antigenic mass vaccine dose (48 HA units/dose)) resulted in substantially lower HA-specific antibody titers (mean HI titer > 4 log2), but still reduced viral shedding from the oropharynx by more than 5-fold in comparison to the non-vaccinated control. In contrast, the commercial vaccine not only failed to effectively reduce shedding in comparison to the non-vaccinated control, but exacerbated oropharyngeal shedding until day 21 after viral challenge, illustrating the antigenic dissimilarity between the commercial vaccine and a recent field virus. Plant-produced VLP vaccines, which facilitates differentiation between infected and vaccination animals (DIVA), presents a new generation of poultry vaccines that is highly efficacious and cost-effective with the major advantage of producing a tailored antigenically-matched vaccine candidate within a short space of time and holds enormous potential for the poultry industry. / Thesis (PhD)--University of Pretoria, 2020. / Production Animal Studies / PhD / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/76794 |
| Date | January 2020 |
| Creators | Smith, Tanja |
| Contributors | Abolnik, Celia, tanja.smith29@gmail.com, O'Kennedy, Martha M. |
| Publisher | University of Pretoria |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | © 2020 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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