contagion

A disease spread by contact.

The spread or transmission of such a disease.

The spread of anything likened to a contagious disease.

It is true, they were a good-natured and respectable set of servants, who had lived so long in their places that they might be said, by a happy contagion, to have caught kindly feelings from their superiors, and, having assisted in saving the lives of the young ladies, gave them an interest in their pleasures, and a real delight in seeing those fair young faces lighted up with joy.

The spread of anything likened to a contagious disease.

And it was German procrastination that aggravated the Greek crisis and caused the contagion that turned it into an existential crisis for Europe.

A recession or crisis developed in such manner.