For those that come later:
The following work for WOTLK
hasDisease = Lua.LuaDoString<bool>("for i=1,40 do local _, _, _, _, debuffType = UnitDebuff('player', i); if debuffType == 'Disease' then return true; end end");
if (hasDisease && SpellManager.SpellUsableLUA("Abolish Disease") && ObjectManager.Me.ManaPercentage > 10 && !ObjectManager.Me.HaveBuff("Abolish Disease") && !ObjectManager.Me.InCombatFlagOnly) {
Interact.InteractGameObject(ObjectManager.Me.GetBaseAddress);
AbolishDisease.Launch();
Lua.LuaDoString("ClearTarget();");
hasDisease = false;
}