RESEARCH Antigen dose and humora o r

Full list of author information is available at the end of the articlecontagious disease causing high mortality in juvenile sal-monids. The disease was first reported as catarrhal en-teritis mainly affecting fingerlings in North America in the 1940s [1] although the virus was first isolated and characterized in 1960 [2]. It is a double stranded RNA virus and a prototype member of the Aquabirnavirus in the Birnaviridae family [3]. The expansion of aquacul-ture which has led to intensive fish farming has resulted in an increase in outbreaks not only in fingerlings but also in postmolts [4]. To reduce the occurrence of vaccines able to reduce mortality and post challenge per-sistent infections [5-8]. Although several strategies have been explored to develop efficacious vaccines, success has been limited by the general failure of most vaccines to produce long lasting immunity that reduces mortality and eliminates post challenge persistent infections. Factors leading to vaccine failure have been reviewed by different scientists. In 1986, Olesen and Jogensen [9] reported that antibody responses in salmonids were in-herently variable and that they could not be correlated with protection. A subsequent study carried out by Bootland et al. [10] in 1990 showed that inactivated vac-cines were able to reduce mortality but did not preven