Abstract
Disease-free rainbow trout (Salmo gairdneri) in Europe have a natural (6 S) serum protein capable of inactivating a tissue culture-adapted isolate of infectious pancreatic necrosis virus, IPNV strain Sp (M. DORSON et al., C.R. Acad. Sci., 281, 1435-1438, 1975). We examined five distinct stocks of rainbow trout (from virus-free Canadian facilities) and all expressed a similar inhibitor that neutralized IPNV Sp in fathead minnow (FHM) cells at maximum (reciprocal) mean serum titers ranging from 128 to 512 (80 % plaque reduction, 0.1 ml inocula). Tests with different laboratory strains of virus, including Jasper, Buhl, Reno, Powder Mill, VR 299, OV, and Tellina virus (TV), indicated that greatest activity was directed against TV but Jasper and VR 299 were inactivated nearly as well by a typical serum preparation. Viral inhibition was slightly greater in the cyprinid (FHM) cell line than in the salmonid (CHSE-214) line. However, preparations of viruses that did not produce significant cytopathic effects (CPE) in FHM cells were comparatively insensitive to serum inhibition as determined in CHSE-214 cells. Buhl and Powder Mill were refractory to neutralization, as were VR 299 preparations without FHM-IPNV variants. Oyster virus (OV) was inhibited by normal trout serum, but to a considerably decreased extent compared to the Sp FHM-IPNV strain or to the serum-sensitive North American IPNV strains.
