Susceptibility of whirling disease (WD) resistance and WD susceptible strains of rainbow trout Oncorhynchus mykiss to Tetracapsuloides bryosalmonae, Yersinia ruckeri and viral haemorrhagic septicaemia virus

Abstract

The focus of this work was to examine the susceptibility of a German rainbow trout strain (H) along with a North American strain (TL, which is highly susceptible to whirling disease) to three pathogens: the myxozoan parasite Tetracapsuloides bryosalmonae, which causes proliferative kidney disease (PKD), the bacterium Yersinia ruckeri, which causes enteric red mouth disease (ERM) and VHS virus, which is the causative agent of viral haemorrhagic septicaemia. Exposure to T. bryosalmonae was conducted under field conditions for 6 days in a hatchery long known to be endemic for the parasite. Fish were then transferred to our wet laboratory and held under controlled conditions until the end of the experiment at 16 weeks. Infection trials with Y. ruckeri and viral haemorrhagic septicaemia virus took place under controlled laboratory conditions, and lasted 21 days.Infections were confirmed by observation of clinical signs, histology and PCR, for all the pathogens investigated. For ERM, an additional bacteriological examination was carried out and for VHS; viral infection was confirmed by cell culture. At least one of these methods confirmed infection in all fish that died following challenges. The German strain H was found to have similar susceptibility as that of the American strain TL to all three pathogens investigated; there were no significant differences in the course of the diseases, clinical signs or mortality.