Oh yes, the article nails the reason:  the algae produces PSP in full force when it hits stomach acid.  No acid in our mouths means no PSP until you swallow the shellfish with the algae in it.  Poof you're dead.

Here's the URL for the test kits from Jellett, which was funded by the Alaska Science & Technology Foundation.  If anyone knows of a local vendor, please post it.  http://www.jellett.ca/psp_test.php?page_id=13