Haemato-immunological responses and effectiveness of feed-based bivalent vaccine against Streptococcus iniae and Aeromonas hydrophila infections in hybrid red tilapia (Oreochromis mossambicus × O. niloticus)

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background: </jats:bold>Streptococcosis<jats:italic> </jats:italic>and Motile Aeromonad Septicemia (MAS) are important diseases of tilapia,<jats:italic> Oreochromis</jats:italic> spp. and causes huge economic losses in aquaculture globally. The feed-based vaccination may be an alternative to minimize major infectious diseases in tilapia. Thus, this study aims to evaluate the haemato-immunological responses and effectiveness of a newly developed feed-based killed bivalent vaccine against <jats:italic>Streptococcus iniae</jats:italic> and <jats:italic>Aeromonas hydrophila </jats:italic>in hybrid red tilapia. A total of 495 hybrid red tilapia of 61.23±4.95 g were distributed into 5 groups (each with triplicate). The fish were immunized orally through bivalent (combined <jats:italic>S. iniae</jats:italic> and <jats:italic>A. hydrophila</jats:italic>) spray vaccine (BS group), bivalent formulate vaccine (BF group), monovalent <jats:italic>S. iniae </jats:italic>vaccine (MS group),<jats:italic> </jats:italic>monovalent <jats:italic>A. hydrophila </jats:italic>vaccine<jats:italic> </jats:italic>(MA group)<jats:italic> </jats:italic>and unvaccinated as a control group. The vaccine was orally administered on days 0, 14 and 42 applied feed-based bacterin at 5% body weight. The blood and spleen samples were collected from all groups on 7, 21 and 49 days post-vaccination, and also 96 hours post-infection to assess their haemato-immune responses. <jats:bold>Results:</jats:bold> Compared with the unvaccinated group, leukocyte, lymphocytes, monocytes, granulocytes counts in vaccinated groups were significantly (<jats:italic>P </jats:italic>&lt; 0.05) increased on 21, 49 days post-vaccination and also 96 hours post-infection, while erythrocytes, haemoglobin and haematocrit in vaccinated groups were significantly (<jats:italic>P </jats:italic>&lt; 0.05) enhanced only 96 hours post-infection. Additionally, the lysozyme and phagocytic activity and, serum antibody (IgM) were significantly higher (<jats:italic>P</jats:italic> &lt; 0.05) against <jats:italic>S. iniae</jats:italic> and <jats:italic>A. hydrophila</jats:italic> in vaccinated groups compared to the unvaccinated group in the pre- and post-infection. Results from the challenge through co-infection with <jats:italic>S. iniae</jats:italic> and <jats:italic>A. hydrophila</jats:italic> showed the relative percent survival (RPS) in BF group was 76.67±4.71%, which had the capacity to induce significant protection (<jats:italic>P</jats:italic> &lt; 0.05) compared to others groups. <jats:bold>Conclusions:</jats:bold> This study demonstrates the bivalent formulate (BF) group could elicit significant non-specific and specific immunological responses with higher protection in hybrid red tilapia. In addition, this newly developed feed-based bivalent vaccination can be a promising technique for effective and large scale fish immunization in the aquaculture industry.</jats:p>