I see, thanks for the answer, Zulg and merry x-mas!

Then I have another question: if there is a saving throw on rot each tick, svs spell is in play too? Or is it just like 50x50 and gear will not take part in this calculation?

I've played shamans and a lot of people died to the rot earlier. I think rot have a very high chance to decrease con. But some people never died to it (and I know they had no +con gear and I've rotted them with best rot available). So, trick is saves?

Thanks!