AUTHOR=Wu Tonglei , Ma Ruitao , Pan Xiaoyi , Wang Fengjie , Zhang Zhiqiang , Shi Qiumei , Shan Xiaofeng , Gao Guisheng 

TITLE=Comparison of the efficacy of Aeromonas veronii ΔhisJ vaccine in Carassius auratus via different immunization routes

JOURNAL=Frontiers in Veterinary Science

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2024.1378448

DOI=10.3389/fvets.2024.1378448

ISSN=2297-1769

ABSTRACT=<sec><title>Introdction</title><p><italic>Aeromonas veronii</italic> is a significant pathogen to various aquatic life. Infections in fish can lead to high mortality rates, causing substantial economic losses in aquaculture. Vaccination is proposed as a substitute for antibiotics in aquaculture to decrease disease-related mortality and morbidity. Our study previously constructed a <italic>hisJ</italic>-deleted strain of <italic>A. veronii</italic>, which provided protective effect to <italic>Loach</italic>.</p></sec><sec><title>Methods</title><p>To further assess the vaccine’s applicability, this study evaluated its genetic stability and safety, and the immune protective effects in <italic>Carassius auratus</italic> through four distinct administration routes: intraperitoneal injection, intramuscular injection, oral administration, and immersion, to determine the efficacy of these administration routes.</p></sec><sec><title>Results</title><p>The results showed that the vaccine remained genetically stable after 45 generations. Immunization via these administration routes was safe for <italic>Carassius auratus</italic>, with intraperitoneal and intramuscular injections causing stronger adverse reactions. Immersion immunization resulted in mild adverse reactions, and no significant adverse reactions were observed following oral immunization. Immunizing <italic>Carassius auratus</italic> at safe concentrations via these routes enhanced the phagocytic activity in serum, increased the levels of non-specific immune-related enzymes (ACP, AKP, C3, C4, LZM, SOD, and IgM), and improved specific serum antibody levels. It also elevated levels of cytokines related to inflammatory responses (IL-1β, IL-10, TNF-α, TGF-β) in organ tissues (liver, spleen, kidney, mid-post intestine, and gills). The survival rates of <italic>Carassius auratus</italic> were measured after challenging with the virulent strain <italic>A. veronii TH0426</italic>, resulting in the relative survival rates of 64% for Intraperitoneal vaccine group, 56% for Intramuscular vaccine group, 52% for oral vaccine group, and 48% for immersion vaccine group. Analysis of bacterial load in the liver, spleen, and kidney post-challenge showed a decreasing trend in the control group, indicating that the vaccine strain <italic>ΔhisJ</italic> could gradually restrict the rapid proliferation of bacteria in these tissues, thereby providing a certain level of immune protection against <italic>A. veronii</italic>.</p></sec><sec><title>Discussion</title><p>In brief, the vaccine strain <italic>ΔhisJ</italic> can serve as a safe live attenuated vaccine for <italic>Carassius auratus</italic>, and this study lays the foundation for the development of live attenuated vaccines against <italic>Aeromonas veronii</italic>.</p></sec>