Cholera is a case in point. In Britain, this once-feared disease is now almost unknown, banished by the separation of sewage and supply lines after its cause - polluted water - was identified in Victorian times. But that required a huge investment in our sewerage system. In countries such as Bangladesh and parts of South America, the disease remains an ever-present danger.
There, the idea of vaccination is uneconomic. The present vaccine has, in any case, only a 50 to 60 per cent effectiveness in reducing clinical illness for a maximum of six months, and primarily in the first two months after vaccination. It has also been shown to be of no benefit in controlling the spread of disease.
Instead, it needs a bit of lateral thinking to find a solution. Amazingly, it seems that a team of scientists, led by Rita Colwell from the University of Maryland, in the United States, and the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh, has achieved the ultimate: a cost- free method of preventing the disease. The answer: clothing - saris, to be precise. Anyone who wears a sari, or knows someone who does, has the required technology to provide water that is virtually guaranteed not to lead to cholera, at any time.
The route to their solution requires an understanding of the microorganism and processes that leads to cholera. The bacteria that cause it - known as vibrios - are drunk along with contaminated water. Once in the gut, they release a toxin which causes severe diarrhoea and vomiting. This leads to the sufferer becoming severely dehydrated and, in many cases, it causes death.
Professor Colwell and her colleagues made a study of the biology of the bacterium. They found that the bacteria normally live in the gut of tiny plankton-like organisms known as copepods. Each copepod carries thousands of cholera bacteria; drinking only a handful of these, carried in dirty water, could cause the disease. And that happens with regularity. Plankton blooms occur in spring and autumn in Bangladesh, and each bloom is invariably followed by an outbreak of cholera.
Sterilising the water by boiling seems an obvious preventative measure - but it fails the economic test. Wood for fuel is too scarce in Bangladesh.
The scientists therefore turned their thinking around. Rather than killing the copepods and bacteria once they are in the water that the person intends to drink, why not find a way to remove them before drinking? Tests of water samples from Bangladesh showed that filtering out the copepods would remove the bacteria.
In fact, they discovered that filtering water through four layers of sari material reduced the number of cholera vibrios by more than 99 per cent - dramatically reducing the chances of consuming a dose large enough to cause cholera. Four layers of cloth turned out to be the optimum number: more led to clogging of the filter but no improvement in efficiency. "This method should save many lives," says Professor Colwell. This is especially true after the plankton blooms, when the risk of an epidemic is highest.
Sari material is just as good as - or better than - other materials for filtration. This was important, say the team, as it can be found in every household in Bangladesh. "This means that it is affordable even to the poorest of the poor."
But won't the sari material become contaminated? Again, the economic argument is no problem. Decontaminating the material is free: two hours in direct sunlight (a commodity not in short supply in the tropics) is sufficient to kill off the bacteria trapped in the material. In the monsoon seasons, cheap disinfectants can do the trick.
Preliminary field trials will begin next year to ensure that villagers will use the method correctly. This will be followed by a two-year study to compare the incidence of cholera between several villages using the new technique and those that do not. If, as expected, it is a success, then the method will be publicised throughout Bangladesh.
It might seem surprising that such a simple, effective remedy has never been produced by the techniques that have produced so much other folk wisdom. Yet it is clear that an understanding of cholera's particular biology is required, along with some way of measuring the effectiveness of the filtration technique. And because it would not work during monsoon (because the decontamination would often fail) it would be the sort of experiment in folk wisdom which would quickly fall into disrepute.
Thus, although the procedure is a simple one, it has taken many years of research to produce. Because the tiny bacteria are attached to the much larger plankton, they can be filtered out - but no one realised this until the Maryland team's work.
All the hard work should soon pay off. As Professor Colwell comments: "If this simple and direct approach can reduce the number of cholera cases - and especially death caused by cholera vibrio - then we will be very pleased to have made a contribution to the improvement of the health and welfare of our fellow human beings."
It's just that it's not often you can do this by using somebody's clothes.