sick = just sick would be a cold or flu type thing but usually it's just sick so your just feel off

disease = like a cut that got infected, it has a clear sign, or a tooth that gets infected depression manic behavior things like that

virus = something inside that has no sign, which will eventually lead to being sick, can be noticed but only if you use your own machines, hospitals cannot be trusted, must rely on GOD

plague = rapid spreading nearly instantly worldwide

across the globe

with Airtraffic

any place that is allows traffic

can happen in less than 20 mins