Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Contagious

Contagious as activity.
—Anonymous

Contagious as a yawn.
—Anonymous

Contagious, like the gladness of a happy child.
—Edward Bulwer-Lytton

Contagious as the smile of a keeper showing you through the wards of a madhouse.
—James H. Gardiner

Contagious, like silliness.
—Arsène Houssaye