The Shifting Definition of Viruses

Written by Mike Stone on September 24, 2026. Posted in Current News

From the earliest days of the field, scientists were never in agreement about what “viruses” actually were. Some believed they were tiny bacteria, others thought they were chemical poisons, ferments, or even processes generated within the host itself.

For decades, there was no clear definition of a “virus,” and the concept remained fluid and speculative.

As historian of science William Summers acknowledged, the category of “virus” was essentially constructed and continually re-constructed by scientists over time. As scientific tools and theoretical frameworks changed, so did the definition of what a “virus” was supposed to be.

Eminent virologist Thomas Rivers acknowledged in the early 1930s that “viruses” were initially defined by absence: they were invisible under ordinary microscopes, passed through certain filters, and could not grow outside living cells. Even Rivers admitted that reliable data about the true nature of “viruses” was lacking.

French microbiologist André Lwoff later played a key role in redefining “viruses” in 1957 as genetic entities that depend on host cells. Yet even this modern definition largely relied on negative characteristics—describing “viruses” by what they supposedly lack rather than what they are.

Taken together, these historical sources reveal that the concept of the “virus” has never been stable. Rather than emerging from a steady accumulation of facts, the idea has evolved through shifting interpretations shaped by technology, theoretical trends, and the assumptions of researchers at the time.

For a more detailed examination, please see my article Inventing the Nature of “Viruses.”

source  viroliegynewsletter.substack.com