Is there any risk of illness from eating raw mushrooms?

Fresh mushrooms may contain Clostridium botulinum, the cause of botulism. In the absence of oxygen, the pathogen can grow and produce toxins before visible signs of spoilage appear. Therefore, do not store mushrooms in airtight plastic bags. For best results, store them in a paper bag.
 
Fresh mushrooms also are subject to mold growth, particularly if exposed to moisture. Plastic wraps tend to promote moisture and should be avoided.
 
Mushrooms can spoil if stored too long. During decomposition, toxins form from mushroom proteins. Eating the mushrooms in their raw or cooked state can cause illness, so they need to be inspected carefully for signs of spoilage.
 
Source(s):
Canadian Food Inspection Agency "Packaging and storage of fresh mushrooms"
En.foodlexicon.com "Fungus Mushroom, Edible Mushrooms..."