Development of an immune complex vaccine to control variant Infectious Bursal Disease Virus infection in the Canadian broiler chicken industry
Date
2020-05-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-4520-5507
Type
Thesis
Degree Level
Masters
Abstract
We have previously demonstrated that vaccines used in Canada against infectious bursal
disease virus (IBDV) are not effective in controlling variant IBDVs (vIBDVs) in the broiler
chicken industry. The objective of this study was to develop an immune complex (Icx) vaccine
using vIBDV SK09 to immunize broiler breeder parents to protect their progeny broilers against
vIBDVs. The immunoprotective ability of broiler chicks carrying maternal antibodies (MaAb) or
control groups with no MaAb against IBDV was studied by challenging with vIBDV SK09, SK10
or SK11 at day-6 of age. The immunoprotective efficacy of SK09 vaccine formulations were
compared with commercial IBDV vaccines used in broiler breeders. Bursa of Fabricius (BF)
samples were collected at 3, 6, 9, 13, and 29 days post-challenge for viral load detection using RT-
qPCR.
Viral load peaked at 3-days post- challenge (dpc) in broiler chicks obtained from
unvaccinated breeders as well as in broiler chicks obtained from broiler breeders immunized with
commercial IBDV vaccines. However, viral loads decreased later in these groups but were
significantly higher compared to our IBDV vaccine formulation groups. Viral load in the BF of
broilers was not detected up to 13 dpc in all progeny groups from parents vaccinated with SK09
Icx. However, we detected significantly higher viral loads in the BF samples obtained from these
groups at 29 dpc. This data suggests that passive immunity induced by breeder vaccination
programs were able to protect broilers against vIBDV challenge at least up to 13 dpc. Nevertheless,
they failed to provide sterile immunity as viral load significantly increased at 29 dpc. This data
further suggests that delayed viral replication or probably challenged vIBDV hiding somewhere
in broiler chicks that showed up when MaAb waned. It shows that B-lymphocytes significantly
depleted in unvaccinated control and commercial vaccine groups by 3 dpc by flow cytometry. In
contrast, B-lymphocyte numbers were normal in other groups up to 13 dpc; however, by 29 dpc
B-lymphocytes were significantly depleted in all breeder vaccine programs. Altogether, our data
suggest that the broiler breeder vaccination program against vIBDV SK09 can protect broiler
chicks for the first three weeks of age but may not be able to provide complete protection even
against vIBDV as SK09. Hence, this study demonstrates the importance of introducing a broiler
vaccine to control vIBDVs circulating in the Canadian broiler chicken industry.
Description
Keywords
IBDV, immune complex, vaccine
Citation
Degree
Master of Science (M.Sc.)
Department
Veterinary Pathology
Program
Veterinary Pathology