Most commonly there are 3 basic and elementary pathological sources from which food poisoning is associated with. The following general categories are listed below along with examples:
1. Virus (best examples: Hepatitis A and E) - liver infection
2. Bacteria (E. Coli, Salmonella, Shigella, etc) - a whole variety of GI and systemic diseases
3. Fungi (best example: poisonous mushrooms) - severe liver damage and liver failure
There is a very unusual and rare 4th one, most elementary in chemical composition, known as a prion. The common term for the illness is Mad Cow Disease.