Viruses

Viruses, which are too small to be seen with a light microscope, are self-replicating infectious agents that often cause disease. They consist mainly or entirely of a nucleic acid genome, either RNA or DNA, enclosed in a protective protein coat (i.e., nucleoprotein) known as a capsid. As obligate parasites, viruses can replicate only in suitable living cells of a host organism. Unlike most pathogens, viruses do not consume the cells of their host or produce other compounds to kill their host. Instead, viruses take over the metabolic processes and biomaterials of the host cell for their own replication. Viruses are classified according to their shape or structure, chemical composition, and mode of replication.

Viruses are common plant pathogens and cause many serious diseases in agricultural crops. Viruses can also be beneficial as natural control agents or used by humans as biocontrol agents (i.e., produced by and spread artificially by humans). Although many types of viruses may cause disease in Canadian trees, none are currently known to be overly damaging or widespread. Only one virus of concern, affecting poplars, is found in the database.