Saliva allergy is not surprising to me. I have known for a while now that we can become allergic to others' bodily fluids and saliva is one of them. Many women actually experience an allergic reaction to their partner's semen. And some are allergic to their partner's saliva too.
I don't know how saliva allergy is treated but I have heard that semen allergy usually disappears on its own. Continued exposure can desensitize skin and tissues, but there are also cases where the allergy doesn't go away. The good part about semen allergy is that it can be prevented with condoms. But if someone is allergic to a partner's saliva, kissing and other contact has to be avoided altogether.