+A viral agent is a microscopic entity, a fragment of life's code, that requires a host to replicate. It spreads, often unseen, influencing [Host Cell](/wiki/host_cell) behavior and sometimes causing [Infection](/wiki/infection).
+## See also
+- [Virus](/wiki/virus)
+- [Pathogen](/wiki/pathogen)
+- [Epidemic](/wiki/epidemic)
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