 [ Symptoms ] i have fever several times a day with pressure in lower abdomen [ Disease ] theories about what causes crohn is disease abound but none has been proven the most popular theory is that the body is immune system reacts to a virus or a bacterium by causing ongoing inflammation in the intestine people with crohn is disease tend to have abnormalities of the immune system but doctors do not know whether these abnormalities are a cause or result of the disease crohn is disease is not caused by emotional distress