Pox and Variola major

Pox noun - A contagious disease characterized by purulent skin eruptions that may leave pock marks.

Variola major and pox are semantically related. In some cases you can replace phrase "Variola major" with "Pox", this terms are similar.

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.

Pox and variola major are semantically related. You can use "Pox" instead a noun phrase "Variola major".