Board Thread:Support Requests - Community Management/@comment-24859896-20170630195627/@comment-26611127-20170701031559

You can use Special:Contact to alert Staff about your problem. They might have some ideas on how to alleviate the situation. I doubt, however, that they will disable the Discussions feature on your wiki.

I guess my suggestion would be to promote more trusted individuals to moderator status in order to stop the spam.