The term diarrhea should be restricted to the frequent passage of loose watery stools. The term dysentery applies to stools that contain blood and is often associated with fever. Dysentery is a much more serious condition.
Diarrhea is a common problem for travelers worldwide and is caused by many bacteria that the local people have become accustomed and immune to since childhood. It can not be entirely avoided but your risk is less when you eat well-cooked foods and avoid poorly cooked sea foods in particular. It is a self limited illness and usually requires no treatment other than rest and increase of fluid intake. If it persists for more than 2-3 days, consult a physician. We do not recommend the use of prophylactic antibiotics for travelers.
Dysentery manifesting with bloody stools, fever and pain should be evaluated and treated by a doctor. It can be caused by bacillary or parasitic infections and may require specific treatment with antibacterial or antiparasitic drugs depending on the cause.