Virus

One of a group of minute infectious agents, characterized by a lack of independent metabolism and by the ability to replicate only within living host cells. (Bondad-Reantaso, M.G., McGladdery, S.E., East, I. & Subasinghe, R.P. (2001) Asia diagnostic guide to aquatic animal diseases. FAO Fisheries Technical Paper, (402/2): 237p.)