By default SquidClamav scan all HTTP stream.
Add here your exceptions for virus scanning, i-e any regular expression a la grep typed here that must abort virus scanning when found in a client URL request or in the Content-Type HTTP header.
Any special character must be escaped with a backslash.
Example:
To abort scanning on URL matching the following extensions: ^.*\.(css|xml|xsl|js|html|jsp)$ To abort scanning on content-type matching the following patterns: ^image\/.*$ ^text\/.*$
If there's no rules defined, SquidClamav Manager allow you to automatically add rules to gain the maximum speed for Squid. Click on the button Optimize for speed.