Temperature Variation and Host Immunity Regulate Viral Persistence in a Salmonid Host.

Area of Science:

• Environmental science
• Virology
• Immunology

Background:

• Environmental factors significantly influence host-pathogen dynamics and epidemic patterns.
• The interplay between host immunity and environmental conditions in modulating virus fitness within hosts is not fully understood.

Purpose of the Study:

• To investigate the combined effects of water temperature and host immune responses on the persistence of infectious hematopoietic necrosis virus (IHNV) in steelhead trout.
• To differentiate the direct impact of temperature on viral replication from its interaction with host immunity.

Main Methods:

• In vitro cell culture experiments to assess IHNV replication at different temperatures (8, 10, 15 °C).
• In vivo studies with steelhead trout exposed to IHNV across a temperature gradient (6, 10, 15 °C) for 8 months.
• Quantification of viral persistence, host antibody prevalence, fish mortality, and viral RNA localization in tissues.

Main Results:

• IHNV replication was faster at 15 °C compared to 10 °C and 8 °C in cell cultures.
• Fish at 15 °C and 10 °C exhibited higher neutralizing antibody prevalence than those at 6 °C.
• IHNV persisted for shorter durations with lower mortality at warmer temperatures (15 °C) but showed longer persistence and higher virulence in colder temperatures (6 °C) in vivo.
• Viral RNA predominantly localized in kidney and spleen tissues at later time points.

Conclusions:

• Temperature and host immunity interact to determine IHNV persistence within steelhead trout.
• While warmer temperatures enhance viral replication in vitro, colder temperatures promote longer persistence and virulence in vivo due to immune interactions.
• Findings offer insights into host-pathogen responses to climate change, particularly concerning viral diseases in aquatic environments.