Variola minor and Variola major

Variola minor noun - A mild form of smallpox caused by a less virulent form of the virus.

Variola major and variola minor are semantically related. In some cases you can use "Variola major" instead a noun phrase "Variola minor".

Variola major noun - A highly contagious viral disease characterized by fever and weakness and skin eruption with pustules that form scabs that slough off leaving scars.

Variola minor and variola major are semantically related. Sometimes you can replace phrase "Variola minor" with "Variola major", this phrases are similar.