Although vaccination programs are routinely used in terrestrial environments to protect wild and captive populations against infectious disease, their use in fish populations has been limited to aquaculture/hatchery facilities. A major challenge to enacting a vaccination program for wild fish populations is how to efficiently vaccinate large numbers of susceptible individuals. One possible solution to this dilemma would be vaccinating hatchery‐propagated fish prior to their being stocked into infected systems, although the effectiveness of such a program is uncertain. We constructed a spatially explicit individual‐based model to evaluate the effectiveness of vaccinating hatchery‐propagated fish to protect wild Lake Michigan Chinook salmon Oncorhynchus tshawytscha against a disease exhibiting characteristics similar to viral hemorrhagic septicemia genotype IVb. Simulations tracked growth, movement, mortality, maturation, wild reproduction, and disease transmission during a 25‐yr time period. Disease states consisted of vaccinated, susceptible, infected, shedding (i.e., infectious), and recovered. Factors that were examined included level of clustering among at‐large individuals, infection probability, relationship between viral exposure and mortality, number of stocked individuals, whether recovered individuals could resume viral shedding, and disease initialization status. At an annual stocking level of 2.4 million Chinook salmon, vaccination decreased the percent of the population infected by 23–74% per year depending on the factors evaluated. Doubling the stocking level of vaccinated individuals resulted in similar levels of protection. The largest decrease in percent infected occurred under a condition of low infection probability, high exposure mortality, and high degree of clustering. The protection stemming from vaccination was just slightly smaller under conditions of high infection and high exposure mortality. Complete disease eradication only occurred when recovered individuals could not resume viral shedding. Under such conditions, vaccination sometimes was not even necessary for disease eradication. Our modeling efforts showed that a vaccination program based on immunizing hatchery‐propagated individuals prior to stocking may help protect wild fish populations, although disease eradication may be difficult to achieve when recovered individuals can resume shedding viral particles.
Ecosphere – Wiley
Published: Jan 1, 2018
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