Comment 22 for bug 53856

The things that are critical for clamav are:

Virus definitions - these are updated through freshclam.
Security fixes - these are being updated through the security updates. Since clamav is in Universe the fact that you are getting the security fixes goes beyond what Ubuntu has promised to do.

So, you are getting what you need in a stable release and, as is appropriate, no more. I think what you need to do is quit over-reacting to log messages.