There are no viruses that afflict OS X. The only mal-ware are things like DNS re-directs but you have to consciously choose to install them. It takes admin level authorization to do. There will never be protection against that!
So, there is no need for anti-virus software. There are unusual examples of acting as a good neighbor if you ever intercept a virus laden PC document, but any PC left so unprotected is already hosed.