RegEx in Microsoft Word Find/Replace to locate an unescaped semi-colon in index markers

I’ve got Find/Replace open, under More I have Use wildcards checked.

I have a LOT of index markers in my document, and I want to find semicolons inside the index markers that are NOT escaped. I want to only find semicolon (;) not a semicolon preceded by a backslash (;), there may be more than one semicolon that needs to be located in a single index marker, and I want to add the backslash in front of any semicolons that don’t already have the backslash in front of them.

I’ve reproduced a couple of my index markers below.

{ XE "afráðskollr:damage-head; burden-head; a man who causes suffering and setbacks" }
{ XE "ganimaðr:impetuous man; hothead" }

I’ve tried experimenting, but I am not getting even the search part right. Heaven help me when I try to replace a plain semicolon with an escaped semicolon! I’m probably having issues between my knowledge of real RegEx vs. what MS Word is using here.

Any advice would be most welcome!