A Mac in itself is very unlikely to be infected, but it can still load an infection and transfer it to another computer.
If it is part of a setup where it may transfer infections, there are a few steps that can be taken to prevent or minimize this.
Since I do not own a Mac or have a lot to do with them, your best idea would be to ask in the section of the forum that deals with Macs
Under the operating systems area is one sub-area devoted only to discussion on Mac computers only.
I feel that they will have more specific answers to this question, since most of us will only seek help from Google on the subject -
Thank You - Mac OS -
Use this forum to discuss, ask questions, and give answers for the operating systems developed, marketed, and sold by Apple Inc.
Edited to add Mac OS area link -
Edited by noknojon, 22 August 2012 - 05:32 PM.