Evaluation of killed Aeromonas hydrophila whole cell vaccine against acute infectious abdominal dropsy in Indian major carps

Abstract

A whole cell vaccine was prepared by using a formalin killed highly virulent strain
of Aeromonas hydrophila isolated from Indian major carps suffering from acute
infectious abdominal dropsy in Andaman. Ten numbers each of Cirrhinus mrigala,
Catla catla and cat fishes were vaccinated by intraperitoneal (I/P) injection and
immersion bath. Four weeks after vaccination, the efficacy was tested by
challenging with virulent strain of A. hydrophila @ 1.5 x 109/0.2ml/fish by I/P. The
relative percentage of survivability (RPS) was observed at 100, 75 and 60 in 1/
P vaccinated group against 45, 25 and 20 in immersion group respectively. Strong
agglutinating and precipitating antibodies were present in I/P vaccinated group
in contrast to mild delayed type reaction in immersion bath vaccinated group.
However, wide range of individual variation in both the agglutinating and
precipitating antibodies was observed. Microscopic observation of blood cells from
vaccinated and control groups and the primary antigen-antibody reactions
indicated that both cellular and humoral antibodies are involved in protection, and
even the detectable level of agglutinating as well as precipitating antibodies are
enough for protection. Since I/P vaccination in fish population is not a feasible
proposition, a live attenuated vaccine for use either as immersion or in the form
of biofilms is urgently required