Immigration. The song's other title was "They're coming to America", it's a song about american dream, and opportunities which america gives.
Possible points to discuss: both claimed millions of lives and spread quickly across country borders; no one understood the cause of either disease; no one had a cure for either disease; diagnosis was almost certainly a death sentence; people often deserted those who fell ill because of the fear of contagion spreading; suppositions of how one could become infected were often not true; animals were involved in the initial spread of each disease (rats and primates); neither disease had an official name for quite some time.
hmm thats a tough one because an effective leader would need a little of both to know what to do in the times of crisis and then follow through with his plan.
