There's literally no such thing as viruses. However... in 1923 the scientific community used the term "virus" to describe a microbe smaller than a bacteria....that they all HYPOTHESIZED to exist as the electron microscope had yet to be invented in the mid 1930s. They literally lacked the technology to see such a thing in the first place.

Thus, all those alleged deadly outbreaks prior to the mid-1930s blamed on hypothetical viruses like rabies, spanish flu, polio, smallpox, etc. were nothing but speculation.

And here's the kicker; even thought the technology has existed to see something of this size for the past 90-odd years, this is still true today as nobody has ever found a so-called virus in the real world. Rendering the idea of a "man-made" virus even more ludicrous.