Histopathological Changes Following Vaccination of Oil-Based Vaccine in Cobia Rachycentron cadadum

Abstract

     Most vaccines used in aquaculture are killed or inactivated pathogens. The goal of vaccination is the generation of immune response to administer antigen able to provide long - term protection against infection. To achive this objective, it requires the addition of an adjuvant. Among adjuvants, oil adjuvants are the most common used for vaccine in aquaculture. However, there were few studies describing mechanism reaction to oil adjuvant in fish. This study injected killed a polyvalent vaccines imulsified with Montanide TM ISA 760 adjuvant against V. alginolyticus, V. parahaemolyticus, and V. harveyi causing Vibriosis in cobia Rachycentron canadum. The muscular tissues at the injection site was sampled at day 7, 14 và 21 post vaccination and fixed by buffer formaline 10% for histological observations. Histological sections were cut and stained by H&E to observe structure changes caused by oil adjuvant. The result showed the the oil droplets deposited in the muscle and the muscular fibers were broken at the injection site 7 days post vaccination. At 14 dyas post vaccination the sign of immune response with inflammatory cells surrounding the oil droplets forming granuloma.The inflamatory lesions and granuloma were observed more obvious at y 21 days post vaccination. This study indicated that oil-based vaccine not only induced cellular immune response but also caused serious side - effects at the injection site in cobia.