We are so good at minimising risk that we do it without even thinking. There are certain animals that would never drink still water - and we are one of them. Only in desperation would we consider drinking from water that is not fresh and flowing. We walk very gingerly on ice (that is, if we have to) and avoid certain poisonous animals. The oddest thing, though is that one of the most poisonous and dangerous creatures in the world does not live in some far off outpost but actually lives among us. That creature is the common housefly.

Through good housekeeping and the use of Insect-o-cutor fly killers, house flies can be kept in check. If such measures are not taken then you are at risk. The illnesses spread by houseflies are potentially deadly but in most cases lead to just a few days of sickness. In areas where fresh water is not in ready supply, even minor outbreaks of disease carried by flies can have alarming consequences.

Cholera This is a particularly nasty disease and strikes in areas where there are drought conditions. The sad thing is that the best prevention and cure is fresh water and not expensive medicines. This is OK for those of us living in areas where water is easy to come by but the outbreak of cholera in a drought-ridden area can be disastrous. The bacterium vibria cholerae causes the disease and one of the main carriers, especially in the disease's early cycle, are flies. The symptoms of cholera are diarrhoea containing flecks of white; sunken eyes and dry mouth; stomach pains; dry skin, nausea and usually vomiting. In children, the soft spot at the top of the head may be sunken. The best cure is lots of fresh water.

Escherichia coli (E Coli) This is usually not serious. The most notorious strain of this disease is the O157:H7 strain that can lead to kidney failure in young children. This is extremely rare. There is usually no need for treatment. This organism can be found on many fresh foods, especially beef. It is spread by a variety of means including, of course, the fly.

Shigellosis Usually not serious, but very unpleasant in the worse cases. Symptoms of Shigellosis can range from it being unnoticeable to the production of bloody diarrhoea.

Typhoid Fever Even the mention of Typhoid Fever can send a shiver down the spine. This goes back to the days before antibiotics. One in five of untreated sufferers will die from this disease. Antibiotic treatment will usually cure the patient in a few days.

The key thing about the above illnesses is that they are spread by flies, and there are many others not mentioned here. In rich countries this is serious. In poor or drought-ridden countries this is deadly.