There is a famous phrase in Shakespeare's Romeo and Juliet, spoken by Mercutio:
A plague o' both your houses!
This phrase is often alluded to in contemporary writing. But in the 20th century, many of the allusions replace the word plague with pox.
Reaching for quick examples is not hard. This quote from a letter in The Providence Journal was published less than one hour ago as of this writing:
That said, a pox on both our political parties. They have frittered away our future with their inability to control their desire to spend other people’s money.
This article in the Sun Herald appeared less than 12 hours ago:
The whole goal of both parties is power. Link that to campaign contributions. A pox on all their houses!
This article on CNN.com was published on November 28, 2017 and quotes the phrase spoken by a U.S. Senator:
"I think the American people will look at all of us and say 'I can't believe you people didn't pass this bill. How did you make it out of the birth canal? A pox on all your houses,'" Louisiana Sen. John Kennedy said.
My question is pretty straightforward: Is there a reason this phrase is often alluded to with the word "pox" replacing "plague?" For instance, was the phrase with "pox" used by a significant author or spoken by a prominent figure in a way that prompted the phrase to become increasingly used in altered form?
Additional Notes
eNotes writes:
Mercutio's famous line might not be exactly the one Shakespeare wrote: instead of "a' both your houses," various old editions have "on your houses," "a' both the houses," "of both the houses," and "a' both houses." The line as I've given it here is merely editorial reconstruction—in other words, a good guess at what the "original" might have looked like, if there was only one original.
However, there seems to be wide agreement that the original text uses the word "plague."
This nGram graph shows that the change appears to have taken place in the 20th century.