Methods of producing, propagating and multiplying viruses, methods of identifying the presence of a virus in a sample, specifically methods using Japanese eel cell cultures. Also provided are an isolated Japanese eel cell culture, optionally infected with a virus, vaccines comprising viruses grown according to the methods of the invention, and a kit for propagating viruses comprising the Japanese eel cell culture. The virus may be a fish virus such as nodavirus, Infectious Pancreatic Necrosis Virus (IPNV) and Salmon Pancreas Disease Virus (SPDV).

A method of producing attenuated cells for a mammalian vaccine comprising killing or attenuating the cells with a high energy, low heat UV light.

A composition for treating a lysogenic virus, including a vector encoding isolated nucleic acid encoding two or more gene editors chosen from gene editors that target viral DNA, gene editors that target viral RNA, and combinations thereof. A composition for treating a lytic virus, including a vector encoding isolated nucleic acid encoding at least one gene editor that targets viral DNA and a viral RNA targeting composition. A composition for treating both lysogenic and lytic viruses, including a vector encoding isolated nucleic acid encoding two or more gene editors that target viral RNA. A composition for treating lytic viruses. Methods of treating a lysogenic virus or a lytic virus, by administering the above compositions to an individual having a virus and inactivating the virus.