Infectious diseases of salmonid fish: Risk factors and disease dynamics

The standard epidemic model was used as the basis for the estimation of the critical minimum threshold density for an epidemic of infectious pancreatic necrosis (IPN) in rainbow trout fry (Oncorhynchus mykiss). The estimated value of the transmission parameter, $\beta$, declined exponentially as the initial density of susceptible fish increased. Two estimates of the critical minimum threshold density resulted from the experiments: 9.5 fish per liter and 3.25 fish per liter. In another set of experiments, rainbow trout fry were exposed to IPNV, then distributed into three tanks, or combined with unexposed rainbow trout fry. The rate of virus excretion per fish increased from day 4 to day 8, then decreased. Susceptible fish became infected with IPNV within two days after exposed fish began to excrete virus. By day 9, 85% of the susceptible fish were infected with IPNV. The transmission parameter, $\beta$, was 0.05. A retrospective whole-population survey was used to identify risk factors for bacterial gill disease (BGD) in young rainbow trout in North America. For the analysis of all cases of BGD, there was a significant association between mortality from bacterial gill disease and previous experience with BGD outbreaks, being a commercial hatchery, and being a hatchery with an annual salmonid fish production $\u3e$250,000 fish. For BGD outbreaks in the hatch house, the presence of fish in the hatch house water supply, use of ultraviolet radiation to disinfect the hatch house water, previous experience with bacterial gill disease, and being a commercial hatchery significantly increased the odds of an outbreak. The odds of an outbreak outside the hatch house was significantly associated with previous BGD and being a hatchery with an annual salmonid fish production $\u3e$50,000 pounds

Infectious diseases of salmonid fish: Risk factors and disease dynamics

The standard epidemic model was used as the basis for the estimation of the critical minimum threshold density for an epidemic of infectious pancreatic necrosis (IPN) in rainbow trout fry (Oncorhynchus mykiss). The estimated value of the transmission parameter, $\beta$, declined exponentially as the initial density of susceptible fish increased. Two estimates of the critical minimum threshold density resulted from the experiments: 9.5 fish per liter and 3.25 fish per liter. In another set of experiments, rainbow trout fry were exposed to IPNV, then distributed into three tanks, or combined with unexposed rainbow trout fry. The rate of virus excretion per fish increased from day 4 to day 8, then decreased. Susceptible fish became infected with IPNV within two days after exposed fish began to excrete virus. By day 9, 85% of the susceptible fish were infected with IPNV. The transmission parameter, $\beta$, was 0.05. A retrospective whole-population survey was used to identify risk factors for bacterial gill disease (BGD) in young rainbow trout in North America. For the analysis of all cases of BGD, there was a significant association between mortality from bacterial gill disease and previous experience with BGD outbreaks, being a commercial hatchery, and being a hatchery with an annual salmonid fish production $\u3e$250,000 fish. For BGD outbreaks in the hatch house, the presence of fish in the hatch house water supply, use of ultraviolet radiation to disinfect the hatch house water, previous experience with bacterial gill disease, and being a commercial hatchery significantly increased the odds of an outbreak. The odds of an outbreak outside the hatch house was significantly associated with previous BGD and being a hatchery with an annual salmonid fish production $\u3e$50,000 pounds