"parastitic" is not a word. So it shouldn't be a tag parastitic. I assume this should have been "parasitic"... but, honestly, that's a pretty weird word both to read and to pronounce, at least for me. I'd rather us fix it by going to "parasite".
Somebody already edited the four questions to change the tag, but the tag with the typo had a wiki so can't be auto-deleted. I edited to remove the wiki (which was only one sentence anyway), but the editor required that I supply a wiki excerpt in order to make the edit. So I did that; I think the excerpt won't prevent the tag from being auto-purged, but please check back in a couple days and let us know if it's still there.
I also renamed the new tag from "parasite" to "parasites". Noun tags work better as plurals.
In this case there were only four questions so it didn't matter, but in the future, if we need to rename a tag that's on a lot of questions, it's better to have a moderator do the rename instead of individually editing (and bumping) all the questions. Only moderators can rename tags.