Pestilence deals disease damage overtime to a target. When that target dies, if pestilence was still active, it spreads to 2 nearby enemies. Pestilence continues as long as there are nearby enemies and they are killed before its duration expires.
The above disease damage amounts (322-394(107-131), 394-481(131-160), 429-525(143-175), 501-612(167-204), 572-700(191-233)) are with STR 80 (no worn armor or items, no buffs and no AAs)