How could a plague that killed off the dinosaurs come back?

In my story, something pretty insane happens during the 3rd season.

The common conception was that an asteroid strike contributed to the extinction to dinosaurs, but unbeknownst to all it was not a giant impact that killed them off; it was actually a world wide plague that destroyed them.

The plague has now returned in modern day. The plague spreads world wide and is deadly for humans, though certain races are more immune than others.

My question is this; what is a scientifically realistic way this could happen? If a plague did indeed kill the dinosaurs how could the plague:

A) Become stagnant for millions of years and disappear from history?

B) Only to return again in modern day to wreck havoc for a second time. Whether it be by the hands of a scientist or through some other event. It returns and hits hard.

C) Be deadly to humans despite being tens of millions of years old?

Trivia

Simple facts about the plague:

• It is only deadly for certain living things, unfortunately humans make the list.
• It affects cell motility.
• Roughly 30% of individuals have some degree of immunity towards it with race playing a factor. No one has complete immunity (at least not naturally).
• It spreads fast.

Note: While I was originally only looking for hard science answers, I am now accepting any explanations that are at least within the realm of realism. Hard science answers are still welcomed though if anyone has anything to contribute. But I've come to understand that the nature of my question makes hard science quite limited.

posted over 5 years ago

Noble‭

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