Review of infectious agent occurrence in wild salmonids in British Columbia, Canada.

Wild Pacific salmonids (WPS) are economically and culturally important to the Pacific North region. Most recently, some populations of WPS have been in decline. Of hypothesized factors contributing to the decline, infectious agents have been postulated to increase the risk of mortality in Pacific salmon. We present a literature review of both published journal and unpublished data to describe the distribution of infectious agents reported in wild Pacific salmonid populations in British Columbia (BC), Canada. We targeted 10 infectious agents, considered to potentially cause severe economic losses in Atlantic salmon or be of conservation concern for wild salmon in BC. The findings indicated a low frequency of infectious hematopoietic necrosis virus, piscine orthoreovirus, viral haemorrhagic septicaemia virus, Aeromonas salmonicida, Renibacterium salmoninarum, Piscirickettsia salmonis and other Rickettsia-like organisms, Yersinia ruckeri, Tenacibaculum maritimum and Moritella viscosa. No positive results were reported for infestations with Paramoeba perurans in peer-reviewed papers and the DFO Fish Pathology Program database. This review synthesizes existing information, as well as gaps therein, that can support the design and implementation of a long-term surveillance programme of infectious agents in wild salmonids in BC.

Bayesian latent class analysis of ELISA and RT-rPCR diagnostic accuracy for subclinical Renibacterium salmoninarum infection in Atlantic salmon (Salmo salar) broodstock.

Renibacterium salmoninarum infection causes bacterial kidney disease (BKD) in salmonid freshwater and saltwater life stages, with potentially severe financial loss for the aquaculture industry. Preventing vertical transmission, from infected broodstock to eggs, is key to disease management. As there is no perfect reference standard for detecting R. salmoninarum, we used Bayesian latent class analyses to compare real-time reverse transcriptase PCR (RT-rPCR, mRNA target) and enzyme-linked immunosorbent assay (ELISA; p57 antigen target) diagnostic accuracy for detection in Atlantic salmon broodstock from British Columbia, Canada, and assessed ELISA repeatability. In 2016, 4,544 Atlantic salmon broodstock (no clinical signs of BKD or gross lesions) were sampled for ELISA testing of kidney tissue. Two groups of ELISA positives (n = 132) and two groups of a random sample of ELISA negatives (n = 137) were then tested with RT-rPCR, and ELISA testing was repeated. ELISA testing of broodstock provided the best diagnostic sensitivity (DSe; less chance of false-negative results). The use of joint RT-rPCR and ELISA testing improved DSe over that from each test alone, if a sample was considered positive when either test result was positive. Using these testing schemes in combination with management practices can decrease the likelihood of vertical transmission from subclinically infected broodstock.