Generalities:

Enteritis is an inflammation of the small intestine caused by an infection in the area, caused by pathogens such as norovirus, among others. Enteritis can also be caused by an autoimmune disorder, such as Crohn's disease, certain drugs, radiation therapy, or celiac disease. (autoimmune reaction due to gluten consumption).
When the infection affects other areas of the digestive tract it is called Gastroenteritis or Stomach flu. Inflammation can also involve the stomach causing gastritis and/or the large intestine causing colitis.
Necrotic enteritis is caused by clorstridium Perfringens.

Symptoms:

Enteritis usually presents with abdominal pain, inflammation, vomiting and diarrhea.