For viral and bacterial agents to cause inflammatory disease involving the gastrointestinal tract, nonspecific host defense factors of gastric acidity, gastrointestinal motility, enteric flora, barrier functions of mucus secretion and mucosal integrity (in some cases), and specific enteric mucosal immunity and systemic immune mechanisms have to be overcome.
These infections can results in vomiting, diarrhea, and abdominal pain, in addition to systemic effects such as fever. Clinical symptoms vary according to pathogen.
Bacterial virulence is facilitated by enterotoxin secretion (which may be site specific in it action, secreted prior to introduction or while within in the lumen), adherence and invasion of the mucosa, and cytotoxin production, which function to disrupt mucosal and cellular function.
Bacteria can be classified based on their pathological mechanism (Table 1) as well as by their site of activity and the nature of clinical signs and symptoms manifest. Signs and symptoms vary significantly by pathogen and age at presentation, with some forms presenting as crampy abdominal pain with watery diarrhea of relatively short duration, bloody diarrhea, systemic signs and symptoms of inflammation with frank sepsis, and shock. Common bacterial, viral, and parasitic infections involving the colon are outlined in Tables 2 and 3.
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