Nope, avast doesn't delete autonomously, it scans and alerts to infection. If an infection is found, you are required to give your choice of action. So I presume that you didn't get a virus alert when these were received ?
I have no idea how the CA AntiSpam works, so I have no idea how it might interact with avast's localhost proxy it uses to scan email before it hits your inbox.
I use MailWasher Pro and that is independent of the email client, I first have MW Pro check email that found or marked to be spam/suspect is deleted from the email server before it calls OE to download the remainder and that works great for me. There is a free version but it only works with a single email account.