Diarrhoea, dysentery and giardia
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.

Water and food
Water in Peru is better than it used to be, but it can still trouble non-Peruvian (and even Peruvian) stomachs, so it's a good idea to only drink bottled water ( água mineral), available in various sizes, including litre and two-litre bottles from most corner shops or food stores. Stick with known brands, even if they are more expensive, and always check that the seal on the bottle is intact, since refilling with local water is not uncommon. Carbonated water is generally safer as it is more likely to be the genuine stuff. You should also clean your teeth in bottled water and avoid raw foods washed in local water.

Apart from bottled water, there are various methods of treating water whilst you are travelling whether your source is tap water or natural groundwater such as a river or stream. Boiling is the time-honoured method which will be effective in sterilizing water, although it will not remove unpleasant tastes. A minimum boiling time of five minutes (longer at higher altitudes) is sufficient to kill micro-organisms. In remote jungle areas, sterilizing tablets like Potable Agua or liquid iodine are a better idea, although they leave a rather bad taste in the mouth. Pregnant women or people with thyroid problems should consult their doctor before using iodine sterilizing tablets or iodine-based purifiers. In emergencies and remote areas in particular, always check with locals to see whether the tap water is okay ( es potable?) before drinking it. For more information check out www.gorge.net/ham/.

Peruvian food has been frequently condemned as a health hazard, particularly during rare but recurrent cholera outbreaks. Be careful about anything bought from street stalls, particularly seafood, which may not be that fresh. Salads should be avoided, especially in small settlements where they may have been washed in river water or fertilized by local sewage waters.

Altitude sickness
Altitude sickness - known as soroche in Peru - is a common problem for visitors, especially if you are travelling quickly between the coast or jungle regions and the high Andes. The best way to prevent it is to eat light meals, drink lots of coca tea, and spend as long as possible acclimatizing to high altitudes (over 2500m) before carrying out any strenuous activity. Anyone who suffers from headaches or nausea should rest; more seriously, a sudden bad cough could be a sign of pulmonary edema and demands an immediate descent and medical attention - altitude sickness can kill. People often suffer from altitude sickness on trains crossing high passes; if this happens, don't panic, just rest and stay on the train until it descends. Most trains are equipped with oxygen bags or cylinders that are brought around by the conductor for anyone in need.

Traditional medicines
Alternative medicines have a popular history going back at least two thousand years in Peru and the traditional practitioners - herbaleros, hueseros and curanderos - are still commonplace. Herbaleros sell curative plants, herbs and charms in the streets and markets of most towns. They lay out a selection of ground roots, liquid tree barks, flowers, leaves and creams - all with specific medicinal functions and sold at much lower prices than in the farmacias. If told the symptoms, a herbalero can select remedies for most minor (and apparently some major) ailments. Hueseros are consultants who treat diseases and injuries by bone manipulation, while curanderos claim diagnostic, divinatory and healing powers and have existed in Peru since pre-Inca days. For further information on alternative medicine and traditional healing, see Ancient Wizardry in Modern Peru.

What to bring on your trip to Peru in this Peru Weather Guide