Development of feed-based whole-cells inactivated bivalent vaccine and its immunoprotective ability against streptococcosis and motile aeromonad septicemia in red hybrid tilapia (Oreochromis spp.)
Streptococcosis and motile aeromonad septicemia (MAS) are well-known bacterial diseases in tilapia culture, which cause mass mortality with significant economic losses to aquaculture globally. As therapy resistance is an increasing problem, development of efficient fish vaccines seems to be an...
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| Format: | Thesis |
| Language: | English |
| Published: |
2021
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/98592/1/FP%202021%2038%20UPMIR.pdf |
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| Summary: | Streptococcosis and motile aeromonad septicemia (MAS) are well-known bacterial
diseases in tilapia culture, which cause mass mortality with significant economic losses
to aquaculture globally. As therapy resistance is an increasing problem, development of
efficient fish vaccines seems to be an alternative to minimize the streptococcosis and
MAS diseases. The development of feed-based monovalent vaccines in controlling these
diseases has been attempted; however, the mechanism of immunity of feed-based
bivalent vaccine against streptococcosis and MAS infections, and the cross-protective
ability of these two diseases are still understudied. To explore the immunological role of
the feed-based bivalent vaccine, we compared the immune responses of red hybrid tilapia
after immunization with both feed-based bivalent and monovalent vaccines, and
compared the relative percentage survival (RPS) and cross-immunization protections of
red hybrid tilapia following challenged with Streptococcus iniae, Aeromonas
hydrophila, S. agalactiae and A. veronii. A total of five groups of fish were vaccinated
orally through two different techniques; bivalent vaccine (inactivated S. iniae and A.
hydrophila) sprayed on feed pellets (BS group); bivalent vaccine (inactivated S. iniae
and A. hydrophila) incorporated in fish feed (BI group); monovalent inactivated S. iniae
and A. hydrophila vaccine separately incorporated into feed as monovalent S. iniae (MS
group) and monovalent A. hydrophila (MA group); and control group (without vaccine).
The feed based vaccines were delivered orally at 5% of body weight for five consecutive
days and also the double booster doses were administered in the same manner on weeks
2 and 6. The haematological results revealed that BI vaccinated group exhibited
significantly the highest (P < 0.05) number of leucocytes (45.39 ± 1.34 × 103
/µL) and
granulocytes (7.68 ± 0.29 × 103
/µL) on weeks 3 post-vaccination. The lysozyme activity
demonstrated a significant (P < 0.05) increase in BI vaccinated group particularly on 8
(313.77 units/mL) and 12 (303.62 units/mL) weeks post-vaccination. The significantly
(P < 0.05) highest phagocytic activity was also observed in BI group (53.83%), while
the lowest was obtained in BS group (37.33%) on weeks 12 post-vaccination. The enzyme-linked immunosorbent assay (ELISA) analysis showed that BI group developed
a strong and significantly (P < 0.05) higher systemic and mucosal IgM responses against
both S. iniae and A. hydrophila, and also cross-protective antigen S. agalactiae and A.
veronii as compared to the BS vaccine and unvaccinated groups. On weeks 10 post-vaccination, all fish were challenged through the intraperitoneally (i.p.) route, where
relative percentage survival (RPS) in the BI vaccinated group were observed 82.22 ±
3.85% when challenged with S. iniae, 77.78 ± 3.85% when challenged with A.
hydrophila and 77.78 ± 3.85% when co-challenged with both S. iniae and A. hydrophila,
which were significantly higher (P < 0.05) compared to the other groups.
Simultaneously, the BI vaccinated group also showed significantly (P < 0.05) higher
partial cross-protections following challenges with S. agalactiae (RPS at 60.00 ± 6.67%)
and A. veronii (RPS at 57.78 ± 7.70%). Quantitative real-time PCR results also showed
that the relative expressions of IL-1β, C-type lysozyme, TNF-α, TGF-β, CD4, MHC-I,
MHC-II and IgT genes in the BI vaccinated fish spleen, head kidney and hindgut
exhibited various significant (P < 0.05) rising trends following both the early-phase
vaccination and post-infections. Notably, the highest relative expression of IL-1β, MHC-II and IgT genes in BI vaccinated group were observed in the co-infected (S. iniae and
A. hydrophila) fish spleen (9.8 - fold), head kidney (9.6 - fold) and hindgut (24.5 - fold),
respectively.
Combining our results demonstrate that the BI vaccine could elicit significant
immunological responses and this vaccine is highly effective to control S. iniae and A.
hydrophila virulence in red hybrid tilapia, but have moderate efficacy when challenged
with S. agalactiae and A. veronii. Nevertheless, this newly developed feed-based
bivalent incorporated (BI) vaccine can effectively protect tilapia against streptococcosis
and MAS infections, and also could offer a promising strategy for mass fish vaccination
in aquaculture industry. |
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