Please up my topic.
http://www.warmane.com/bugtracker/report/20875
Spell Blood Plague and Frost Fever does not copy the attack power of the Death Knight Rune of the Fallen Crusader and from the Horn of Winter.
When the goal is Blood Plague or Frost Fever and I Use the Horn of Winter, the damage from the disease remains the same, although my attack power increased. The same thing happens when triggered Rune of the Fallen Crusader.
Damage from disease should come from attack power at the time of periodic damage.