Diarrhoea in its various forms is usually one of the five major causes of death in any emergency situation. The others are malnutrition, measles, malaria and pneumonia. Even outside of emergencies, diarrhoea is one of the world's major killers. Up to 2 million children die of it each year. Almost all of these deaths could be quite easily prevented if people had access to basic health care.

Many different micro-organisms can cause diarrhoea: viruses, bacteria, and protozoans. Viruses such as the rotavirus are among the commonest cause of diarrhoea in the world. They cause watery diarrhoea and vomiting, and lead rapidly to dehydration. Bacteria such as Shigella cause bloody diarrhoea, known as dysentery. Other bacteria that commonly cause diarrhoea are those known as Escherichia coli and Campylobacter.

The cholera vibrion is also a bacterium, and the diarrhoea it produces is the most severe and rapidly fatal of all. Protozoal parasites can cause persistent debilitating diarrhoea, the commonest forms being giardiasis and amoebic dysentery.

How diarrhoea kills

Diarrhoea causes a person to lose both water and electrolytes. Electrolytes are the salts such as sodium and potassium which are essential to the functioning of every cell in the body.

If vomiting accompanies the diarrhoea then these losses are accelerated. The loss of water and electrolytes leads to dehydration. This happens especially quickly in a child. The child becomes irritable, and its mouth is dry. Its mother may notice that it is passing urine less frequently, and when it cries there may be no tears. As dehydration progresses, a nurse or doctor will notice other signs as we

ll. The skin turgor is decreased, which means that when a fold of skin is pinched up from the abdomen it stays raised up for a moment, even after it is let go. Also, the eyes sink down into the orbits. The pulse becomes rapid and weak. By this stage, the internal organs are all suffering. They lack both water and electrolytes, and begin to fail. The child is in shock and falls into a coma, and soon after that the heart stops beating, which is termed cardiac arrest. Death from dehydration usually occurs when 10 to 15% of the total body weight is lost. In severe diarrhoea such as that caused by cholera this may take only a couple of hours.

Managing a diarrhoea epidemic

An epidemic of diarrhoeal disease is always a risk in an emergency situation. Refugees are often crowded together in conditions of poor hygiene and sanitation. There are almost always high numbers of cases of diarrhoea. And if cholera breaks out, it may spread like wildfire. The key to managing an outbreak of diarrhoea is being prepared and setting up a sound system of logistics. MSF teams generally assume that they will have to deal with large numbers of dehydrated people, and prepare themselves accordingly.

Preventing diarrhoea

There are no effective vaccines against any of the micro-organisms causing diarrhoea. The only way to prevent its spread is to interrupt the faecal-oral cycle of contagion.

An example - teaching nomads to save their children

The nomads of the Ogaden region of Ethiopia and Somalia do not usually have access to safe drinking water. Mostly they take their water from shallow dams called birkas which they have dug to catch rain water. The water is shared with the goats and camels that are such an important part of the culture and economy. Because this is surface water (rather than ground water, such as from a spring or a well) it is almost always polluted.

The children often get diarrhoea, and as the families do not have frequent contact with health facilities or even markets where the mothers could buy ORS, it is important to find simple ways of preventing and treating dehydration. The strategy used by MSF teams is to teach the mothers to make their own rehydration solution.

MSF treatment for diarrhoea

The treatment of diarrhoea is essentially the treatment of dehydration - which involves simply replacing all the fluid being lost. This process is called rehydration. MSF treats many patients using oral rehydration solution, called ORS. This is a mixture of glucose and electrolytes (such as sodium and potassium) that comes in sachets.

Each sachet is stirred into a litre of water and provides the correct balance of electrolytes to rehydrate a cholera patient. It has been said that in global terms ORS is the most important medical discovery since penicillin. However, many of our patients, especially those with cholera, vomit so profusely that they cannot drink ORS.

MSF therefore treats serious cases by putting in intravenous drips. These IV infusions contain fluid and electrolytes. Some patients lose fluid so quickly that they need two drips, one in each arm. The challenge for an MSF doctor or nurse is to find a vein in a profoundly dehydrated patient - for as the patient loses fluid their veins collapse.

Treating serious cases requires a high degree of skill and experience. In most cholera outbreaks MSF teams are able to limit the case fatality rate to less than 1 per cent.

Most forms of diarrhoea do not require any treatment other than rehydration. Cholera patients, however, are usually given an antibiotic called doxycycline, which has been shown to shorten the period of severe diarrhoea. Another form of diarrhoea, Shigella dysentery, also requires antibiotics, because of the serious complications that may accompany it.