1Malina M. Loeher; 1Hannah Brown; 2Gael Kurath; 1Andrew R. Wargo
1Virginia Institute of Marine Science, William & Mary, Gloucester Point, VA, USA, 2USGS Western Fisheries Research Center, Seattle, WA, USA
Emergent pathogens remain a major challenge in the globally intensifying aquaculture industry. Infectious hematopoietic necrosis virus (IHNV) emerged in rainbow trout (Oncorhynchus mykiss) aquaculture in the 1970s following a host jump from its endemic host sockeye salmon (Oncorhynchus nerka). Since emergence in aquaculture, IHNV has rapidly diversified beyond its endemic range. There is evidence of increased virulence evolution post-host jump, but other fitness traits such as transmission rate are largely unstudied. Transmission rate is rarely measurable and instead is typically estimated by within-host pathogen loads, or more rarely pathogen shedding into the environment, for example through quantification of viral loads in water. These methods inherently assume pathogen loads are directly correlated to transmission rate, but lack empirical evidence to support this assumption in fish or other host-pathogen systems. We conducted an in vivo host-to-host transmission study using a fish cohabitation design. Fifty replicate donor fish were dosed with one of two viral isolates via bath immersion and separated into individual tanks. Naïve recipient fish were inserted into donor tanks for three discrete cohabitation periods, days 1, 3, 5 post-infection, which is known to be the primary window of viral shedding. After cohabitation, recipient fish were separated into individual tanks and sampled to assess transmission success. Water samples were analyzed via digital qPCR. This work examines how viral shed rate and transmission success are linked and provides additional system-specific empirical data. Inference of transmission dynamics at the individual and population levels will allow epidemiological models to more accurately predict pathogen spread and subsequently mitigate virulence risk.