To quote the orc helpfile: "Living in squalor since the time of their creation, Orcs have a strong
immune system..."

An inherant ability of orcs could be to allow them to 'burn off' or purge out their systems of disease or poison. I see this being a utility type ability that would have the following restrictions depending on the implementation:

either: Could only be done outdoors in forests, swamps, caves or water, no deserts or frozen area for the following reason:

Orcs live in squalor, familiar with swamps and muck. Part of the ability would be to find leeches they'd apply to their skin to suck out the poison. Obviously, leeches don't (Although arguably, half the orcs in the orc village are covered with slime and leeches anyway)

Or: When used, would inflict minor bleeding for a few ticks for the following reason:

The orc, used to more savage methods of medicine would attempt to bleed out the poison/disease. Poison and disease (if having them at the same time) would be replaced by minor bleeding damage that would last a duration of a few hours.

Reuse of the skill would be 24 hours in both cases, since the orc would need to get his/her strength back up since both require loss of blood, regardless of how implemented