Virulent Plague

You create a 15ft swirling cloud of virulent plague. Creatures of your choice must succeed on a Constitution saving throw or become afflicted by the plague

While afflicted, the target suffers the following effects:

• Its movement speed is halved.
• It has disadvantage on attack rolls and ability checks.
• Must make a Constitution Save at the start of each of its turns  the afflicted takes 2d8 necrotic damage on a failed save, or half as much damage on a successful one. 
  
  If an infected creature dies while under the effects of this spell, it also explodes and creatures of your choice within 15ft can must make a Constitution save or become infected by the plague.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the necrotic damage increases by 1d8 for each slot level above 3rd.