Health

Health Check: Blue is the colour for sleeping sickness cure

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Media captionMaryam Abdalla reports on the blue targets luring tsetse flies

Scientists trying to eradicate the insect which spreads sleeping sickness in sub-Saharan Africa, have found that the tsetse fly has a weakness for the colour blue - and it could be the key to making the disease disappear.

The waters of the River Anyau in northern Uganda appear beautiful in the afternoon sun, while children play in the shallow water, but they also act as a breeding ground for a small fly that spreads a deadly disease.

Along the banks of the river, every 50 metres or so, small rectangular pieces of blue material are visible, attached to wooden stakes in the ground, contrasting with the surrounding greenery.

They are insecticide 'targets' for tsetse flies - and in the past six months, 35,000 of them have been dug into riverbanks in the West Nile region of northern Uganda as part of a project developed by researchers from Liverpool School of Tropical Medicine.

The aim is to reduce the tsetse fly population, which transmits a parasite to humans causing sleeping sickness.

'Feeling weak'

If the illness is not picked up and treated early - which is difficult because signs of the disease are not immediately obvious - then it is often fatal.

Mark Ojoma, a father of six who lives by the river in Arua, realised that he was affected just in time.

"I was having a headache, I was having swollen joints and my body weight was low.

"And I was feeling weak and I was sleeping now and then. Even in the daytime I used to sleep."

Mark was lucky and survived, but many haven't.

Image copyright LSTM
Image caption The targets have been placed along the edge of rivers, lakes and swamps where the tsetse fly breeds
Image copyright MARTIN DOHRN/SCIENCE PHOTO LIBRARY
Image caption Sleeping sickness is caused by a bite from a tsetse fly which transmits a Trypanosoma parasite

At the height of the most recent African epidemic in the 90s, the World Health Organization estimates that around 300,000 people were infected every year. Most died because few were diagnosed and treated.

As a result, the WHO made sleeping sickness, or Human African trypanosomiasis, a public health priority as one of 17 neglected tropical diseases.

In 2009, cases of sleeping sickness dropped to below 10,000 for the first time in 50 years - and the decline continues to this day.

Aiming for blue

Prof Mike Lehane, project leader from the Liverpool School of Tropical Medicine, who has been working with French researchers from Montpellier, says the blue targets "are an opportunity to get rid of the disease as a public health problem for good".

His colleague Dr Richard Selby, says the new method of combating the disease by going after the tsetse fly by rivers, lakes and swamps is cheap as well as effective.

"The flies are attracted to the blue material, they circle it and land on a black netting attached to it which they can't see.

"They hit that, it's covered in insecticide, they pick up the chemical, fly off and die within three minutes."

Early monitoring of the success of the targets suggests that they are having a "huge impact", Dr Selby says, reducing the fly population by around 90%.

This is possible because the tsetse fly is very sensitive to insecticide and an extremely slow breeder, producing just one live offspring every nine days.

Mosquitoes, in contrast, produce hundreds in the same timeframe.

What's more challenging is reaching the places where the flies live and breed, because they tend to be remote and difficult to access.

But it is communities in rural areas of sub-Saharan Africa, who depend on agriculture, fishing and hunting, who are most at risk from the disease.

'Washed away'

In northern Uganda, Dr Selby says local people have bought into the idea of the blue targets, allowing the research team to enrol the help of local government officials in placing them.

This means the project team can begin to step back and let local teams take on the tsetse fly.

The targets won't last forever though, he explains.

"If placed well, they will last about five months. Because they need to be near water they are usually washed away during heavy rains.

"So we have to deploy them again during the dry season."

Image copyright LSTM
Image caption Screening for sleeping sickness is not easy in the early stages of the disease

A few kilometres from Arua, in Omugu, the Liverpool team have also been testing the blood of villagers to accurately assess the current scale of sleeping sickness - and they will do the same tests again in 18 months to see how effective the targets have been.

Picking up the presence of the parasite in the blood is difficult in the early stages of the disease.

If the disease is left to develop, however, the parasite will multiply and cross into the brain to infect the central nervous system.

This is when more obvious signs of the disease appear, such as confusion, changes in behaviour, and disturbances in sleep patterns, which give it its name.

At this stage, without treatment, sleeping sickness normally ends in death.

More targets

A new drug to treat sleeping sickness is in the pipeline and, because it is taken orally rather than intravenously, it holds great promise and should save lives.

Combining screening and treatment with controlling the fly population appears to be the best way of trying to eliminate the disease - and the British team have plans to set up similar projects in other sub-Saharan countries.

With funding from the Bill & Melinda Gates Foundation they want to take their blue targets to Kenya, Chad, Tanzania, Democratic Republic of Congo and Guinea, among others.

There are many more tsetse flies to kill off in remote locations before the disease can really be eliminated for good, but the tiny blue target provides hope that one neglected tropical disease can be controlled once and for all.

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