Virus entry and receptors in fish

A sustainable aquaculture industry depends on control and prevention of infectious diseases. Good health in farmed fish is also beneficial for animal welfare and will prevent the spread of pathogens to surrounding environment. Viral diseases pose a significant threat to the productivity and sustainability of salmon farming and cause significant economic losses. An important step during viral infection is entry of the virus into the host cell; a step where the virus must safely cross the barrier of the cellular membrane of the target cell. Identification of important cellular and viral components that interact during viral entry is essential knowledge for establishing targeted preventative efforts such as vaccines and breeding. The main objective of the VERIFIcation project is to describe the mechanism of binding and entry of piscine orthoreovirus (PRV) into host cells in Atlantic salmon. PRV is the most prevalent virus in Atlantic salmon aquaculture in Norway. The virus is the causative agent cause of heart- and skeletal muscle inflammation (HSMI), which is a widespread disease in farmed salmon. There is currently no commercial vaccine available against HSMI, and the development of a vaccine has been hampered by the failure to grow the virus in known cell cultures. This prevents the use of classic strategies for virus vaccines and infection studies. We have previously found that erythrocytes are the target cells of PRV in salmon. In this project we will study the binding and entry of PRV into these cells. In the project we have established a model that enables us to study the interaction between the virus and the red blood cells. This provides a controlled assay to study the entry process in detail. The model has generated a basic understanding of binding and uptake of PRV into red blood cells. We use this information to investigate what specific viral and cellular factors that are important. The project has successfully identified key viral factors that are central to the process. Furthermore, we have established research tools and method to screen for genes and proteins in red blood cells that are involved. Future work aims at understanding the uptake mechanism in more detail and identify the specific factors important in this virus-host interaction. The work in the project provides knowledge on how the virus causes disease which will be important in efforts for prevention and control of the virus. The project is a collaboration between SINTEF and NMBU, which is highly experienced in fish virology and the methodology that is key to achieving the project goals. Researchers at the University of Pittsburgh (Pennsylvania, USA) with extensive research experience on mammalian viruses closely related to PRV, act as mentors /consultants for the project. Detailed knowledge about binding and entry of PRV is essential to understand disease development and will provide a valuable new tool for vaccine development and possibly also for selective breeding. This could ultimately reduce the prevalence of this virus in Atlantic salmon farming. By using the expertise of human virology research to promote receptor research on fish viruses, we will create a basic toolkit to study the key current and future viral diseases in aquaculture.

Viral diseases pose a significant threat to the productivity and sustainability of aquaculture with over 400 viral disease outbreaks in Norwegian salmon aquaculture annually, causing substantial economical losses to the industry. Sustainable and environmentally responsible aquaculture will require better control and prevention of diseases, to improve fish health, and hinder spread of pathogenic viruses. A key event during infection is the entry of the virus into the host cell. Revealing the entry process and identification of the key cellular and viral components that interact is pivotal to establish targeted preventive efforts. The main aim of this project is to identify the cellular receptor used by Piscine orthoreovirus (PRV) to enter the host cell in Atlantic salmon. PRV is the most widespread virus in Atlantic salmon aquaculture, and the causative agent of heart and skeletal muscle inflammation – an important and widespread disease in farmed salmon. There are currently no vaccine available against PRV infection and development has been hampered by the lack of efficient propagation of PRV in cell culture, making void the classical strategies for viral vaccines and studies of infection. We recently determined that erythrocytes are the target cells of PRV in salmon, and succeeded with purification of PRV. Thus, it is now possible to study the virus cellular uptake, which will be done by two complementary approaches, namely proteome and genetic screening. Identification of the receptor for PRV will provide a valuable new target for vaccine development or selective breeding, that can ultimately lead to reducing the prevalence of this virus in Atlantic salmon aquaculture. By translating expertise built in the human virology sphere to advance receptor research on fish viruses we will create a fundamental toolbox to study the central present and future viral diseases in aquaculture.