Location: Cool and Cold Water Aquaculture ResearchTitle: Aquaculture reuse water, genetic line and vaccination affect Rainbow trout (Oncorhynchus mykiss) disease susceptibility and infection dynamics
|EVERSON, JEREMY - US Department Of Agriculture (USDA)|
|JONES, DARBY - Virginia Institute Of Marine Science|
|TAYLOR, AMY - Virginia Institute Of Marine Science|
|RUTAN, BARB - Virginia Institute Of Marine Science|
|Leeds, Timothy - Tim|
|LANGWIG, KATE - Virginia Tech|
|WARGO, ANDREW - Virginia Institute Of Marine Science|
|Wiens, Gregory - Greg|
Submitted to: Frontiers in Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2021
Publication Date: 9/22/2021
Citation: Everson, J.L., Jones, D., Taylor, A., Rutan, B., Leeds, T.D., Langwig, K., Wargo, A.R., Wiens, G.D. 2021. Aquaculture reuse water, genetic line and vaccination affect Rainbow trout (Oncorhynchus mykiss) disease susceptibility and infection dynamics. Frontiers in Immunology. 12: Article 721048. https://doi.org/10.3389/fimmu.2021.721048.
Interpretive Summary: Infectious disease outbreaks in aquaculture are complex and the environmental factors that influence occurrence are not well understood. Poor water quality is often blamed for disease outbreaks. Here we utilized tanks that were connected to production raceways to examine whether water from fish at a high density affected fish newly exposed to this water for either a brief period of 24 h or for an extended period of 27 days. We examined two different genetic lines of rainbow trout that had been either vaccinated against the infectious hematopoietic virus (IHNV) or were mock vaccinated as a control. We found that water reuse exposure, fish genetic background and vaccination affected survival. The CSF line was more resistant than the Tx-line. Vaccination reduced IHNV prevalence and the mortality of both lines following a pulsed exposure to reuse water. When fish were constantly exposed to the reuse water for 27 days, all fish died, although the CSF line fish died at a slower rate. This study demonstrated that fish could be naturally infected with both IHNV and Flavobacterium psychrophilum at the same time. In summary, exposure to reuse water can initiate complex disease that can overwhelm both innate and vaccine-induced resistance.
Technical Abstract: Infectious hematopoietic necrosis virus (IHNV) and Flavobacterium psychrophilum are major pathogens of farmed rainbow trout. Improved control strategies are desired but the influence of on-farm environmental factors that lead to disease outbreaks remain poorly understood. Water reuse is an important environmental factor affecting disease. Prior studies have established a replicated outdoor-tank system capable of varying the exposure to reuse water by controlling water flow from commercial trout production raceways. The goal of this research was to evaluate the effect of constant or pulsed reuse water exposure on survival, pathogen prevalence, and pathogen load. Herein, we compared two commercial lines of rainbow trout, Clear Springs Food (CSF) and Troutex (Tx) that were either vaccinated against IHNV with a DNA vaccine or sham vaccinated. Over a 27-day experimental period in constant reuse water, all fish from both lines and treatments, died while mortality in control fish in spring water was <1%. Water reuse exposure, genetic line, vaccination, and the interaction between genetic line and water exposure affected survival (P<0.05). Compared to all other water sources, fish exposed to constant reuse water had 46- to 710-fold greater risk of death (P<0.0001). Tx fish had a 2.7-fold greater risk of death compared to CSF fish in constant reuse water (P<0.001), while risk of death did not differ in spring water (P=0.98). Sham-vaccinated fish had 2.1-fold greater risk of death compared to vaccinated fish (P=0.02). Both IHNV prevalence and load were lower in vaccinated fish compared to sham-vaccinated fish, and unexpectedly, F. psychrophilum load associated with fin/gill tissues from live-sampled fish was lower in vaccinated fish compared to sham-vaccinated fish. As a result, up to forty-five percent of unvaccinated fish were naturally co-infected with F. psychrophilum and IHNV and the coinfected fish exhibited the highest IHNV loads. Under laboratory challenge conditions, co-infection with F. psychrophilum and IHNV overwhelmed IHNV vaccine-induced protection. In summary, we demonstrate that exposure to reuse water or multi-pathogen challenge can initiate complex disease dynamics that can overwhelm both vaccination and host genetic resistance.