Believe that this has been done before. How about musing up an Alternative Timeline or musing thru the archives. It is amusing what one will find.
He might have searched for it, yet not have found it.
Many threads probably have both 'horse' and 'plague' in them, despite not being about a 'horse plague'.
As for the archives... are they up again? And, of course, the same search problem applies there, as well.