Contagious Affliction

Speaking words of illness and death, you cause a creature's blood to cloud with toxins and their skin to erupt in lesions.  Make a ranged spell attack against one creature within range.  On a hit, the target takes 2d12 poison damage and becomes infected with a contagious affliction.  On a miss the target takes half damage and is not infected.  

While the target is infected in this way it is poisoned and it must make a Constitution saving throw at the start of each of its turns, ending this effect on a success.  Each time the target fails a saving throw against this effect, it's affliction erupts in a cloud of disease.  This cloud is a sphere with a radius of 10ft centered on the target, and each creature within this sphere when the target fails its saving throw takes 1d6 poison damage.  

This affliction counts as a disease, and can be removed with a Lesser Restoration spell or similar magic.  Undead and constructs are immune to the effects of this spell.  

At Higher Levels: When you cast this spell using a spell slot of 2nd level or higher, the initial poison damage increases by 1d12 for each slot level above 1st and the damage of the poisonous eruptions increases by 1d6 for each slot level above 1st.  Additionally, when you cast this spell using a spell slot of 3rd level or higher, the target takes a -1 penalty to saving throws made against the effects of this spell.  This penalty increases to -2 for a spell slot of 5th level or higher,  -3 for a slot of 7th level or higher, and -4 for a 9th level spell slot.