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Friday, April 23, 1999 Published at 02:43 GMT 03:43 UK


The flies that blind

Flies are linked to the leading cause of preventable blindness, say experts

The major cause of preventable blindness could be significantly reduced by methods to control the spread of flies, according to a study.

The World Health Organisation (WHO) estimates that trachoma has blinded around six million of the world's population - around 15% of the world's blind people.

It also causes painful inturned eyelashes and diahorrea, which kills more than three million children a year in developing countries.

The researchers, led by Paul Emerson of the Medical Research Council in The Gambia, looked at links between flies and trachoma.

They say the insects are commonly overlooked in public health interventions and the way trachoma is spread has yet to be properly studied.

Children's eyes

They studied four villages in the west African country of The Gambia over a three-month period. Two acted as controls.

Parents were asked to monitor diarrhoea outbreaks in their children.

They also studied the flies which came into direct contact with children's eyes.

Over 90% of these were the common Musca sorbens housefly, although it only makes up less than 10% of the total fly population.

Musa domestica made up the remained of eye contacts.

They also found evidence that these types of flies carried the bacteria that causes trachoma and say there is evidence that both are strongly attracted to human faeces and prepared food.

Two of the villages were subject to insectides which control the fly population. This reduced fly-eye contacts by at least 96%.

There were 75% fewer new cases of trachoma in villages with fly controls while diarrhoea was reduced by up to 26%.

Breeding sites

Writing in The Lancet, the researchers say fly control is probably unsustainable on a regular basis.

But they say it could be used when there are trachoma outbreaks when they could reduce deaths from diarrhoea.

They also call for a "definitive study" of the role of flies in transmitting trachoma and for more investigation into cheaper ways of reducing fly populations in developing countries.

They write: "The development and assessment of other sustainable and cost-effective methods for the control of muscid flies, such as the provision of latrines, identification and clearance of breeding sites and assessment of the feasibility of locally made traps, should be a research priority."

The WHO launched a programme in 1997 to eliminate trachoma by 2020.

This included antibiotic treatment of trachoma, improved hygiene and the provision of safer water and sewage services.

In a commentary in The Lancet, Chandler Dawson of the Department of Opthamology at the University of California says there are fears the bacteria that causes trachoma could eventually develop resistance to the main antibiotic used for treating it.

He says this means the other methods outlined by the WHO will have "an essential role" in the control of trachoma.

He backs the researchers' call for urgent attention to be given to other methods of controlling its spread.

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