Study reveals wide variation in virulence among infectious salmon anaemia virus isolates despite similar genetic mutations
Researchers conducted controlled bath challenge experiments with ten isolates of infectious salmon anaemia virus (ISAV) in Atlantic salmon, finding cumulative mortality rates ranging from 15% to 100% despite similar pathogenic genetic markers. The study characterized infection dynamics, viral shedding, and tissue damage across the isolates to understand why field outbreaks show such variable disease severity. The findings suggest that genetic mutations alone do not fully explain virulence differences, which has implications for predicting and managing salmon disease outbreaks.
A standardized freshwater bath challenge study tested ten ISAV-HPR-deleted isolates in Atlantic salmon, including a high-virulence reference strain and nine recent Norwegian field isolates. All isolates established systemic infection but showed pronounced differences in mortality rates (15–100%), infection kinetics, viral shedding, tissue viral loads, and pathological changes, measured through RT-qPCR, histopathology, immunohistochemistry, and flow cytometry. High-mortality isolates (≥90%) shed significantly more virus than low-mortality isolates, with RNA ranges of 10^4–10^6 compared to 10^2–10^3. Genetic sequencing of segments 5 and 6 confirmed all isolates carried typical pathogenic mutations except one with an atypical protease cleavage site mutation. However, these genetic differences alone did not account for the wide biological spectrum of virulence observed, suggesting additional factors influence disease severity.
What's missing
The study does not discuss potential mechanisms beyond genetic mutations that might explain virulence variation (e.g., host factors, environmental conditions, or epigenetic factors). The practical implications for salmon farming management and disease control strategies are not addressed.
What different sources said
- bioRxivCenter
: A standardized bath challenge of Atlantic salmon reveals distinct infection dynamics and mortality across ten HPR-deleted infectious salmon anaemia virus isolates.
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