Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Andrew R Wargo

Committee Member

Jeffrey Shields

Committee Member

Ryan Carnegie

Committee Member

John Hoenig

Committee Member

Dana Hawley


Globally, infectious diseases are responsible for major conservation and economic losses in wild and farmed fish populations. Prevention tools, including vaccination and breeding for genetic disease resistance, are used in many systems to prevent mortality by such diseases. Studies are often done to evaluate the efficacy of a preventative method at reducing disease, but the impact on transmission is rarely studied. Protection under diverse field conditions, such as variable pathogen exposure dosages, is also not fully understood. Furthermore, there is little information on how preventative methods alter host-pathogen relationships. For example, it is largely unknown how vaccination impacts non-target pathogens that co-infect the host. These knowledge gaps make it difficult to infer the epidemiological impacts of disease prevention tools. In an attempt to fill these gaps, we investigated two leading pathogens in rainbow trout (Oncorhynchus mykiss) aquaculture: infectious hematopoietic necrosis virus (IHNV) and Flavobacterium psychrophilum. We evaluated the impacts of vaccination and genetic disease resistance on mortality and transmission across a range of challenge dosages of IHNV and F. psychrophilum to accurately reflect field variability. There was evidence of a dosage effect; as dosage increased, shedding increased and vaccine efficacy decreased. We also evaluated how vaccination and genetic disease resistance impact transmission dynamics during simultaneous and sequential co-infection of IHNV and F. psychrophilum. Our results indicate co-infected fish shed more of both pathogens than they do in single infections, and the order that the pathogen infected the host may impact transmission in both pathogens. Furthermore, vaccine efficacy may be diminished by co-infection. These studies are aimed at developing a more robust framework for inferring the efficacy of disease prevention strategies. Our results will also help to inform and improve disease management in one of the top aquaculture species in the United States.




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