ASSESSMENT OF CELL MEDIATED AND HUMORAL IMMUNE RESPONSE TO SUBUNIT VACCINE AGAINST RIEMERELLOSIS
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Date
2019-12-30
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COLLEGE OF VETERINARY AND ANIMAL SCIENCES MANNUTHY, THRISSUR
Abstract
Riemerellosis is a bacterial disease among ducks, caused by Riemerella
anatipestifer, which has been well documented as a cause of considerable
economic loss to the duck production in Kerala. At least 21 serotypes of the
organism have been identified globally. Since vaccination is the mainstay for the
control of the disease, a research work was undertaken to prepare subunit vaccine
employing recombinant OmpA of R. anatipestifer and assessment of cell
mediated and humoral immune responses of the vaccine and also to evaluate the
comparative efficacy with that of the developed inactivated vaccine. Broth culture
of R. anatipestifer at a concentration of 2.5 OD values at 525 nm with a dose of 1
mL per bird subcutaneously was selected as LD50.
L per bird subcutaneously was selected as LD50.
A total of 52, day-old ducklings were divided into three treatment groups with
ten birds each. They were injected with 0.5 mL of different types of vaccine
subcutaneously. Group I (T1) served as control with 22 birds including six birds
each for challenge control of inactivated and subunit vaccine. Group II (T2) was
injected with an inactivated vaccine (7x109
cfu/mL), which was prepared as per
the protocol standardised in the Department of Veterinary Microbiology and
group III (T3) and group IV (T4) were administrated with different antigen
concentration of subunit vaccine (equal quantity of the rompA protein (250µg and
500µg) and montanide, respectively). A booster dose was given at third week
post-primary vaccination to T2, T3 and T4. It was observed that, by using both
crude Omp and rOmpA based ELISA, inactivated vaccine birds (T2) produced
higher antibody titre during early age while in the subunit vaccine group, the titre
was higher during later stage. An early antibody response is required to lower the
mortality rate in riemerellosis as the organism targets young ducklings. Thus, it
could be inferred from this study that inactivated vaccine was more effective than
subunit vaccine A significant CMI response was also shown by inactivated vaccine groups
on 14th and 28th day post-vaccination by lymphocyte proliferation assay (LPA).
Challenge studies to assess the protective response revealed 100 per cent protection
for inactivated vaccine group (T2), 80 per cent protection for T4 group and 70 percent protection for T3 group. All the vaccinated birds were having significantly
less gross lesion when compared to the challenge control groups. On analysing the cytokine mRNA expression levels using real-time PCR,
the inactivated vaccine group showed significantly higher (p< 0.05) mRNA levels
of IL-6, IL-12B and IFN-γ gene on day 28 than the two subunit vaccine groups. It
was found that the inactivated vaccine was superior in terms of results obtained
from the challenge study, antibody titre, CMI response and gene expression
analysis than the subunit one. Hence, it is desirable to advocate the use of
inactivated vaccine in field condition owing to its easiness to prepare and low
cost.
Description
Submitted in partial fulfilment of the requirement for the degree of
Doctor of Philosophy in Veterinary Microbiology