These Library of Congress Subject Headings can be searched directly (MERLIN Subject Search) or added to a keyword search, e.g., "public health surveillance and encephalopath*"
Names of diseases are also usually searchable as subject headings.
To find books primarily ABOUT a particular disease, you can look that disease up as a SUBJECT (either Library of Congress/LC or Medical). Look for subject subdivisions like "early works" or"epidemiology" or "epidemics" or "history." Use Subject Search in the MERLIN or MOBIUS catalog. The subject heading "medicine, medievel" is also quite fruitful.
To locate diseases where you can find old sources try KEYWORD searches that incorporate s:, which will locate terms in the Subject field:
s:"early works" and (fever or pox or pestilen* or plague) - you can use other words in parentheses, too.
Try keyword searches using century-terms. Example: epidemi* and 15th century