Evaluation of Different Cell Components of <i>Aeromonas hydrophila</i> on the Immune Response of Rohu (<i>Labeo rohita</i>)

Abstract

The humoral immune response of rohu (Labeo rohita) against different cell components of Aeromonas hydrophila was studied. Heat-killed cells (HKC), formalin killed cells (FKC) and crude lipopolysaccharides (LPS) were prepared from a virulent strain (G-49) of A. hydrophila. Three methods of vaccination were followed, viz., intraperitoneal injection, direct immersion and oral administration through feed. A primary immunization of three vaccines was given on day 0, followed by a 1st booster on day 28 after priming and a 2nd booster on day 28 after 1st booster both for injection and immersion groups. A group of fishes were fed with vaccine-incorporated feed for a period of 14 days during priming, 1st booster and 2nd booster immunization. Antibodies against different immunogens of A. hydrophila were detected using standard method of agglutination on day 0, 7, 14 and 28 following priming and booster immunizations. The degree of protection of all the immunization groups of fish was assessed by challenging the fishes with a LD50 dose of 1.5 x 107 cfu/ml of A. hydrophila on a low titre day after priming and on a peak titre day after 2nd booster. The results showed that the vaccines prepared from FKC yielded higher antibody than HKC and LPS. Vaccines prepared from HKC and LPS offered absolute (100%) protection against challenge. Vaccination with LPS resulted in lower antibody production but better immune protection against challenge in rohu.