Superinfection fitness as a component of overall fitness for a vertebrate RNA virus

Abstract

To gain a greater understanding of the overall fitness of IHNV viral variants, this thesis describes the development of a novel in vivo superinfection fitness assay and the application of this assay to the IHNV-<italic>O. mykiss</italic> system. This assay is the first of its kind to be used to study RNA virus superinfection fitness using reciprocal experimental challenges of a natural vertebrate host with two genetic variants (referred to here as genotypes) of the same virus species to define the dynamics of superinfection fitness. In combination with the single infection, co-infection, and transmission fitness assays described in the introduction, we have applied the novel superinfection assay as well as an environmental stability assay to determine whether virulence is associated with increased superinfection fitness or whether viral genotype displacement events correlate with an increase in viral fitness. By examining many aspects of the virus infection cycle such as entry, in-host replication in co-infection and superinfection, virus transmission potential, and stability in the external environment, we present a more complete understanding of the fitness of the IHNV genotypes tested and the possible correlates of fitness such as virulence or displacement in the field.