Exploring the occurrence and potential associated risk factors for Pilchard Orthomyxovirus (POMV) in Tasmanian farmed Atlantic Salmon
Following basic epidemiology principles, no infectious disease occurs ‘randomly’ and its occurrence follow logical and predictable patterns. The presence of an infectious agent is unlikely sufficient to explain these patterns and most aquatic diseases result from the complex interaction between the agent, the host and its environment. Therefore, the targeted outcome for a POMV control plan is threefold:
1. Decrease transmission between infected and susceptible fish groups – this requires identifying risk factors associated with the introduction, spread, and maintenance of the pathogen within the industry;
2. Decrease the number of susceptible fish – this mainly requires identifying risk factors associated with the susceptibility of the host (e.g. husbandry-related stress) and the development of a safe and effective prophylaxis;
3. Decrease the amount of virus in the environment - this requires detecting infected fish cage(s) early to implement timely control strategies.
Diagnostic capacity to confirmed POMV outbreak has been developed and is currently used in routine by the industry. A vaccine against POMV is currently under development at the Tasmanian Aquatic Animal Health and Vaccines Centre of Excellence and will be available in the future. However, little is known about risk factors specific to POMV and about its full economic impact. We define as a ‘risk factor’ any attribute of the agent, the host or its environment that increases the risk and intensity of a disease outbreak. Most of the environmental risk factors (including farming practices) facilitate the introduction, transmission, or maintenance of the pathogen; while the host risk factors affect the susceptibility of the host and its capacity to become diseased. Like the closely related ISAv, the magnitude and occurrence of POMV outbreaks appeared to be highly variable. This supports the existence of additional factors other than the POMV infection that contribute to the intensity of an outbreak. It is anticipated that by identifying and intervening on some of the manageable risk factors, the frequency and the severity of POMV outbreaks can be reduced.
