Plague Leech - http://www.wowhead.com/spell=123693 - Doesn't remove diseases from the target. Also usable when there is only 1 disease on the target.
1) Should remove diseases (and activate 2 random fully depleted runes).
2) Should only be usable when there are 2 diseases on the target (or necrotic plague - http://www.wowhead.com/spell=152281, which counts for 2)
*1 disease: Tested with Chains of Ice - http://www.wowhead.com/spell=45524
2 diseases: tested with Outbreak - http://www.wowhead.com/spell=77575*