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Wednesday, 19 July, 2000, 23:01 GMT 00:01 UK
Fly trap cuts blindness
flies on face
Swarms of flies are commonplace in some regions
A cheap trap made from plastic pop bottles and dung has significantly cut the number of cases of trachoma - a major cause of blindness.

The simple home-made devices were invented by a retired professor from the Institute of Child Health in London.

Trachoma affects approximately 14m people world-wide, mainly in developing countries.

It is thought to be spread from person to person by the thousands of flies which swarm in certain regions.

In Africa's Rift Valley, for example, there could be as many as 32,000 flies gathered in just one house.

Studies have suggested that simply by reducing the quantity of flies, the risk of transmission of the infection could also be reduced.

Past strategies have involved intensive spraying with insecticide.

However, Professor David Morley developed a fly trap which can be built simply from two transparent plastic bottles, based on his observation that flies, following feeding, tend to fly upwards towards the light.

Fly feast

The lower bottle is plastered with mud to make it dark inside, and then filled with a mixture of goat droppings and cow urine - guaranteed to prove irresistible to flies.

After a fine meal, the flies pass up a plastic tube into a second bottle, left transparent to lure them. Here they die from exhaustion and exposure to UV light.

The bottle went on trial in 300 Masai homes in Kenya over a year.

The fly population was reduced by an estimated 40%, and more importantly, the number of trachoma cases fell by more than a third.

Professor Morley told New Scientist magazine: "Local children have been making the traps at school - the teacher made it part of the homework."

There is still controversy over whether fly population reduction is the key to preventing trachoma cases.

Professor David Mabey, from the London School of Hygiene and Tropical Medicine, said that it was likely the traps would catch many more ordinary "houseflies" than "bazaar" flies, which are blamed for spreading the infection.

He said: "Although I haven't seen this particular research, I find it hard to believe that this method could be very effective."

Earlier research, he said, had found that the bazaar flies liked breeding in human waste - but not if found in a latrine.

Latrine solution

So encouraging villagers to build and use latrines might reduce their numbers.

Professor Mabey is investigating the possibility of treating whole villages simultaneously with one-dose antibiotics to wipe out the "reservoir of infection".

This means that, in theory, there would be no source of infection for the flies to pick up and pass on to others.

Trachoma is the leading single cause of preventable blindness in the world. It is caused not by just one infection, but the legacy of repeated infections over the years.

These cause inflammation on each occasion, and eventually the cumulative damage causes the eyelid to tighten and bend in on itself, prodding the eye with its own lashes and scarring the cornea.

Infections respond well in general to antibiotics, although there are concerns that the bacteria which cause the disease may be becoming resistant to drugs.

Other techniques involve a simple 10-minute operation which turns the eyelid back round the right way, halting the damage.

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See also:

23 Apr 99 | Health
The flies that blind
13 Oct 99 | Health
Webcast fights blindness
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