Viruses must invade living cells in order to replicate. Viuses vary in virulence. Some are very drastic resulting in death, whereas others do not cause disease. The pathogenesis is such that usually young fish become sick while older fish become carriers or resevoir hosts. There are no medications available for use in treating viral diseases of fish.
Prevention is the best method of control as no vaccines are presently licensed for use.
Diagnosis of viral disease is based on observation of clinical signs, history, and virus isolation. Viral diseases are often associated with resevoir hosts. These carriers can shed virus across the gill membranes, through skin muscus, from skin lesions, in excrement, or via reproductive products. This virus can be transmitted directly from infected fish to susceptible fish, or indirectly via the food chain, through water, on nets, buckets, and other equipment. To prevent the spread of viruses and other pathogens, a period of quarantine is recommended for any new additions to an aquarium.