Problem:

There are a lot of food allergies, but for some reason not to meat (mammalian meat or poultry) or mushrooms. I've googled a bit, and now I know that one can actually have a meat or mushroom allergy, although the odds of that are very-very small. Why is it so?

Required:

Question 1: Is it because both meat and mushrooms are usually cooked and that kills potential allergens?

Question 2: What about undercooked or raw food like portobellos or carpaccio and steaks?

Question 3: Is it because animal tissues are so similar to ours and so are better digested?

Question 4: What about mushrooms then? Is it something else?

Question 5: Are there any data of what types of meat and mushrooms are most allergic?