You can search by keyword, and easily figure out what the best keywords are for your topic. It's more efficient, though, to search by Subject Headings. Library of Congress (LC) subject headings follow a predictible pattern -
Disease name -- Place -- time frame
And each of these is dictated by how LC describes each item.
For example:
Leprosy--Europe--History--To 1500.
Leprosy--Europe--History--16th century.
Leprosy--Europe--History--17th century.
Plague (older books use 'Black Death')
Syphilis
So regardless of what words the title uses (pox for syphilis, for example), LC groups titles together by topic using these Authorized Subject Headings. Searching with them or following them from a book description is a very efficient way to find our books on a topic.