A Pathway Toward Solutions for Emerging Trout Virus
The global aquaculture industry continues to expand, reflecting both growing consumer demand for seafood and the shift away from reliance on wild fisheries. Within this sector, the global rainbow trout market represents a significant segment, valued at USD 8.1 billion in 2025 and projected to reach USD 11.2 billion by 2035, with a compound annual growth rate (CAGR) of 3.3%. This steady growth reflects the premium positioning of rainbow trout within the aquaculture market.
Emerging infectious diseases remain a major challenge for aquaculture systems, as most pathogens initially infect mucosal surfaces such as the gills, skin, and gut. Rainbow trout, an important species in inland aquaculture in both the United States and Israel, has recently been affected by a newly identified pathogen, Trout Granulomatous Virus (TGV). This corona-like nidovirus causes chronic liver lesions, gill pallor and lethargy, posing a significant threat to trout health and production.
A collaborative research effort led by Prof. Eran Bacharach (Tel Aviv University) and Dr. Avi Eldar (Kimron Veterinary Institute), in partnership with Prof. Irene Salinas Remiro (University of New Mexico), seeks to elucidate the disease mechanisms and immune responses associated with TGV infection. The team is also developing mucosal vaccines based on DNA platforms and virus-like particles to strengthen disease prevention and preparedness against TGV and other emerging fish pathogens.
Initial findings indicate that Trout Granulomatous Virus infection is associated with extensive gill damage characterized by hemorrhages, edema, lamellar fusion, and granuloma formation. The pathology appears to be primarily driven by maladaptive immune responses rather than by viral load. This virus also seems to be very efficient at persisting in the host long-term by infecting immune cells in the gills and liver and altering MHC-II expression patterns, while also inducing abnormal IgM and pIgR expression, contributing to chronic infection.
Vaccine development efforts are currently underway, including trials of DNA vaccines and recombinant viral vectors expressing the TGV spike protein. Preliminary results demonstrate improved antigen expression, though further optimization is required to enhance membrane targeting and transduction efficiency. These advances contribute to the broader goal of promoting aquaculture resilience through improved disease management and sustainable fish health solutions.
To further contextualize these findings and explore their broader impact, we addressed several key questions with the research team:
How might your findings influence aquaculture health management practices in the U.S. and Israel or globally?
“Our findings suggest that vaccines should target mucosal surfaces like the gills and that effective treatments must seek to uncover hotspots where the virus persists long-term: cells of the immune system.”
Do you see potential for applying this research framework to other emerging aquatic diseases?
“We currently know very little about how farmed fish deal with chronic infections and how these chronic pathogens impact the susceptibility to other disease agents. Another critical point is the importance of when the immune response can become awry contributing to disease severity and favoring pathogens such as TGV. As such, we believe that our work constitutes an invaluable foundation for many other researchers working on fish diseases in the US, Israel and around the world.”
What are your next steps once the vaccine candidates are optimized?
“Once we optimize vaccine candidates, we look forward to optimizing the delivery routes, doses and time for first vaccination so that the rainbow trout commercial production cycle can reduce economic losses due to this pathogen.”
