Studies on Immunization of Trout Against IPN

Abstract

For any vaccine to have practical value in the field, it must be safe (i.e., not produce the disease it is designed to protect against) and it must be effective (i.e., immunogenic enough to induce an effective level of protection). Little progress has been reported to date on the development of a practical vaccine against infectious pancreatic necrosis (IPN) of salmonids. It has been demonstrated (Dorson et al. 1975, 1978) that, after a relatively low number of serial passages through tissue culture, virulent IPN virus develops a sensitivity to neutralization by normal trout serum and at the same time becomes avirulent for trout fry. The neutralization of cell-culture-adapted (CCA) virus by normal trout serum has been shown to be due to an antibody-like non-virus-induced protein which has a sedimentation coefficient of 6S (Vestergard-Jørgensen, 1973; Dorson and de Kinkelin, 1974). It has been reported by Hill and Dixon (1977) that the acquisition of 6S sensitivity by IPN virus is not a permanent mutation or an adaptation process, but a simple selection of a fast-growing tissue culture variant from a mixed virus population, and that this process can be suppressed or even reversed by growth of the virus in the presence of normal trout serum.