This post was published 5 years 6 months 28 days ago. Therefore, it may well be out of date. Do not reply on the contents of this post being accurate. 
Symantec have an article on their US site that advises, at the time of writing, there are no file-infecting viruses that can infect Mac OS X.
They also link to Apple’s page on viruses.
A Mac running with factory settings will protect you from viruses much better than a PC.