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Published on: September 13, 2018
Contaminants as viral cofactors: assessing indirect population effects
Kathrine R Springman1, Gael Kurath, James J Anderson
1Columbia Basin Research, School of Fisheries, University of Washington, Puget Sound Plaza, 1325 4th Avenue, Suite 1820, Seattle, WA 98101-2509, USA. kspringman@ucdavis.edu
Abstract:
Current toxicological methods often miss contaminant effects, particularly when immune suppression is involved. The failure to recognize and evaluate indirect and sublethal effects severely limits the applicability of those methods at the population level. In this study, the Vitality model is used to evaluate the population level effects of a contaminant exerting only indirect, sublethal effects at the individual level. Juvenile rainbow trout (Oncorhynchus mykiss) were injected with 2.5 or 10.0 mg/kg doses of the model CYP1A inducer, beta-naphthoflavone (BNF) as a pre-stressor, then exposed to a challenge dose of 10(2) or 10(4) pfu/fish of infectious hematopoietic necrosis virus (IHNV), an important viral pathogen of salmonids in North America. At the end of the 28-d challenge, the mortality data were processed according to the Vitality model which indicated that the correlation between the average rate of vitality loss and the pre-stressor dose was strong: R2=0.9944. Average time to death and cumulative mortality were dependent on the BNF dose, while no significant difference between the two viral dosages was shown, implying that the history of the organism at the time of stressor exposure is an important factor in determining the virulence or toxicity of the stressor. The conceptual framework of this model permits a smoother transfer of results to a more complex stratum, namely the population level, which allows the immunosuppressive results generated by doses of a CYP1A inducer that more accurately represent the effects elicited by environmentally-relevant contaminant concentrations to be extrapolated to target populations. The indirect effects of other environmental contaminants with similar biotransformation pathways, such as polycyclic aromatic hydrocarbons (PAH), could be assessed and quantified with this model and the results applied to a more complex biological hierarchy.
Insights
This study introduces the Vitality model to assess contaminant impacts on fish populations, revealing that prior exposure to beta-naphthoflavone (BNF) significantly affects mortality from infectious hematopoietic necrosis virus (IHNV). The model effectively quantifies sublethal, indirect toxicant effects at the population level.
Area of Science:
- Environmental Toxicology
- Aquatic Toxicology
- Immunotoxicology
Background:
- Current toxicological methods often fail to detect contaminant effects, especially those involving immune suppression.
- Sublethal and indirect toxicant effects are frequently overlooked, limiting their applicability to population-level assessments.
- The Vitality model offers a framework to evaluate population-level consequences of individual-level toxicant exposure.
Purpose of the Study:
- To evaluate population-level effects of contaminants causing indirect, sublethal effects using the Vitality model.
- To assess the impact of a model CYP1A inducer, beta-naphthoflavone (BNF), on rainbow trout (Oncorhynchus mykiss) immune response and subsequent viral challenge.
- To demonstrate the model's utility in extrapolating individual toxicological data to population-level impacts.
Main Methods:
- Juvenile rainbow trout were exposed to varying doses of beta-naphthoflavone (BNF) as a pre-stressor.
- Fish were subsequently challenged with infectious hematopoietic necrosis virus (IHNV) at different concentrations.
- Mortality data were analyzed using the Vitality model to correlate pre-stressor dose with population-level effects.
Main Results:
- A strong correlation (R2=0.9944) was found between the average rate of vitality loss and the BNF pre-stressor dose.
- Mortality patterns (time to death, cumulative mortality) were dependent on the BNF dose, but not significantly affected by IHNV dosage.
- This suggests that an organism's prior exposure history is critical in determining contaminant and pathogen virulence.
Conclusions:
- The Vitality model successfully quantifies population-level effects of contaminants with indirect, sublethal impacts, such as BNF.
- The model allows for the extrapolation of immunosuppressive effects from environmentally relevant contaminant concentrations to target populations.
- This approach can be applied to assess other environmental contaminants, like polycyclic aromatic hydrocarbons (PAHs), with similar biotransformation pathways.
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