There is no clear cause of appendicitis. Fecal material is thought to be one possible cause of obstruction of the appendix. Bacteria, viruses , fungi, and parasites can result in infection, leading to the swelling of the tissues of the appendix wall. The various infecting organisms include Yersinia species, adenovirus , cytomegalovirus, actinomycosis, Mycobacteria species, Histoplasma species, Schistosoma species, pinworms , and Strongyloides stercoralis . Swelling of the tissue from inflammatory bowel disease such as Crohn's disease also may cause appendicitis.