Evaluation of three alum-precipitated Aeromonas hydrophila vaccines administered to Labeo rohita, Cirrhinus mrigala and Ctenopharyngodon idella: immunokinetics, immersion challenge and histopathology.

F Sughra,F Abbas,I Altaf,M Hafeez-Ur Rahman

doi:10.1590/1519-6984.249913

Abstract

Aeromonas hydrophila is a cause of infectious disease outbreaks in carp species cultured in South Asian countries including Pakistan. This bacterium has gained resistance to a wide range of antibiotics and robust preventive measures are necessary to control its spread. No prior use of fish vaccines has been reported in Pakistan. The present study aims to develop and evaluate inactivated vaccines against local strain of A. hydrophila in Pakistan with alum-precipitate as adjuvant. The immunogenic potential of vaccine was evaluated in two Indian major carps (Rohu: Labeo rohita, Mori: Cirrhinus mrigala) and a Chinese carp (Grass carp: Ctenopharyngodon idella). Fish were vaccinated intraperitoneally followed by a challenge through immersion. Fish with an average age of 4-5 months were randomly distributed in three vaccinated groups with three vaccine concentrations of 108, 109 and 1010 colony forming unit (CFU)/ml and a control group. Fixed dose of 0.1ml was applied to each fish on 1st day and a booster dose at 15 days post-vaccination (DPV). Blood samples were collected on 14, 28, 35, 48 and 60 DPV to determine antibody titers in blood serum using compliment fixation test (CFT). Fish were challenged at 60 DPV with infectious A. hydrophila with 108 CFU/ml through immersion. Significantly higher levels of antibody titers were observed from 28 DPV in all vaccinated groups as compared to those in the control group. In challenge experiment the average RPS (relative percent survivability) was 71% for groups vaccinated with 109 and 1010 CFU/ml and 86% for 108 CFU/ml. Vaccine with 108 CFU/ml induced highest immune response followed by 109 and 1010 CFU/ml. The immune response of L. rohita and C. idella was better than that of C. mrigala. In general, normal histopathology was observed in different organs of vaccinated fish whereas minor deteriorative changes were found in fish vaccinated with higher concentrations of the vaccine.

Highlights

Due to high demand for fish protein, the aquaculture has attracted a lot of attention over the past three decades and has been one of the fastest growing agricultural sectors in the world (FAO, 2018)
Antibody titers of all fish immunized with alumprecipitated vaccines of colony forming unit (CFU)/ml (VA), CFU/ml (VB) and 1010 CFU/ml (VC) respectively were recorded during complement fixation test (CFT) procedure
The antibody geometric mean titers (GMT) value and standard deviations were calculated for each sample

Summary

Introduction

Due to high demand for fish protein, the aquaculture has attracted a lot of attention over the past three decades and has been one of the fastest growing agricultural sectors in the world (FAO, 2018). Infectious diseases are the leading cause of fish mortality in aquaculture, which is predominantly caused by Aeromonas (Hamouda et al, 2019). Among all sub-species, Aeromonas hydrophila is a major cause of outbreaks in aquaculture that has prompted food insecurity and global economic losses (Dash et al, 2014; Aboyadak et al, 2015; Baumgartner et al, 2017). This bacterium causes various infections in fish predominantly haemorrhagic septicemia, dropsy, epizootic ulcerative syndrome, haemorrhagic enteritis and scarlet disease (Igbinosa et al, 2012). Aeromonad infections on fish farms are accelerated by a number of factors including variations in the physical and chemical parameters of pond water

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