This scurvy arc is very bothersome.
While it is true that knowledge of the treatments for scurvy was repeatedly forgotten and rediscovered as late as the 20th century, at no time was scurvy considered a communicable disease (at least, in the Western World).
The knowledge that scurvy was caused by diet was known to Europeans since Antiquity.
There were two actual issues: knowledge of which foods were required to ward it off and having a source of vitamin C which wouldn't spoil during longer voyages.
(Since this seems to be a likely case of the protagonist solving basic problems which the setting is bizarrely and stupidly ignorant of as a staple of the series, I'm probably going to drop it here.)