[Bon mots]

The virus may not have implanted the mutation in the other areas. It would be a rather rare event. But there is substantial evidence that shows that viri have caused several mutations in humans.

The virus could have existed all along in the forests of Europe. At this time, deforestation was going on all over Europe. In England there was a virus that would kill in single day that made the rounds as well... it was called "sweating sickness" and even killed an English royal.

Just as there are now sporadic outbreaks of Ebola in Africa... usually encountered by hunters in the bush, such outbreaks could have been common in the days when Europe had more remote forest lands and more people came into contact with pristine areas.

[shubi]

Probably forms of hemorrhagic fever noun
(1948)
: any of a diverse group of arthropod-borne virus diseases characterized by a sudden onset, fever, aching, bleeding in the internal organs, petechiae, and shock

Merriam-Webster, I. 1996, c1993. Merriam-Webster's collegiate dictionary. Includes index. (10th ed.). Merriam-Webster: Springfield, Mass., U.S.A.