Determination of viral shedding rates, estimation of minimum effective dose, and development of a viral dispersion model for infections hematopoietic necrosis virus (IHNV) in Atlantic Salmon

Description

In British Columbia, IHNV is the most economically important viral pathogen of salmonids. Since the introduction of Atlantic salmon to the BC coast in the mid 1980's, there have been two serious outbreaks of IHN in farmed Atlantic salmon: 1992-1996 and 2001-2003. During the latest epizootic, mortalities were greater than 70% in fish less than 1 kg and averaged 40-50% when fish were larger than 1 kg. Thirty-six farm sites were diagnosed with IHNV during this epizootic. The estimated economic loss resulting from both epizootics was $40 million in inventory representing $200 million in lost sales.

A central question regarding outbreaks in farmed Atlantic salmon is the role of natural waterborne transmission in the spread of virus between farms. Studies investigating spatial and temporal patterns of the IHNV outbreaks suggest that farming practices themselves contributed significantly to the spread of disease both within and between areas; however the extent to which waterborne transmission contributes to virus dispersal during and outbreak is unclear.

IHNV and other related aquatic viruses, such as viral hemorrhagic septicaemia virus, can survive for many days in saltwater at temperatures below 15℃. Therefore, it's not unconceivable that viable and infective IHNV could be transmitted by movement of water from virus infected Atlantic salmon farms to uninfected fish either proximal or distant from the source. Circulation models can be used in developing pathogen dispersal models and in assessing transmission risks. The PBS virology laboratory has established IHNV challenge models and recently developed ultrafiltration methodologies that allow for the concentration of viruses from large volumes of water thereby facilitating the determination of the minimum infectious dose as well as viral shedding rates. Using these established methods, it is the aim of this study to provide quantitative estimates of these parameters for Atlantic salmon post-smolts under controlled experimental conditions and to begin to establish a viral dispersal model and assess transmission risk of IHNV in Atlantic salmon net pen aquaculture.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)

Year(s)

2009 to 2011

Ecoregion(s)

Pacific: Vancouver Island West Coast

Principal Investigator(s)

Kyle Garver
Email: Kyle.Garver@dfo-mpo.gc.ca