Diarrhoea is something everybody gets at some stage, and there’s little to be done except drink a lot (but not alcohol) and bide your time. You should also replace salts either by taking oral rehydration salts or by mixing a teaspoon of salt and eight of sugar in a litre of purified water. You can minimize the risk by being sensible about what you eat, and by not drinking tapwater anywhere. This isn’t difficult, given the extreme cheapness and universal availability of soft drinks and água mineral, while Brazilians are great believers in herbal teas, which often help alleviate cramps.
If your diarrhoea contains blood or mucus, the cause may be dysentery or giardia. With a fever, it could well be caused by bacillic dysentery and may clear up without treatment. If you’re sure you need it, a course of antibiotics such as tetracyclin or ampicillin (travel with a supply if you are going off the beaten track for a while) should sort you, but they also destroy “gut flora” which help protect you. Similar symptoms without fever indicate amoebic dysentery which is much more serious, and can damage your gut if untreated. The usual cure is a course of metronidazole (Flagyl), an antibiotic which may itself make you feel ill, and should not be taken with alcohol. Similar symptoms, plus rotten-egg belches and farts, indicate giardia , for which the treatment is again metronidazole. If you suspect you have any of these, seek medical help, and only start on the metronidazole (750mg three times daily for a week for adults) if there is definitely blood in your diarrhoea and it is impossible to see a doctor.