Assassin's Spit (5e Disease)
From D&D Wiki
This disease is for use in conjunction with the regular Assassin's poison attack. If a creature fails their Constitution and is poisoned, they have ten minutes before disease begins to set in. They roll another Constitution save DC 15. If they pass, they get a fever and the disease dissipates. If they fail, they gain 1 level of exhaustion per dawn until acted upon by a lesser restoration spell or similar magic, or die.