None... clamav, amavis, etc... are used for protecting Windows boxes behind the Linux boxes. If you aren't running any Windows hosts on the
FYI, clamav also detects linux based viruses. There are linux based viruses. Rkhunter is also good to run on a linux server as well.
http://en.wikipedia.org/wiki/List_of_Linux_computer_viruses
Of course if you keep your passwords secure and up to date on patches you 'should' not get any viruses on a linux box. Nothing is certain though. Its very little effort to install clamav and rkhunter.
Matt