A group of London University medical students is preparing for seven weeks of sun, sea and sand flies in a bid to help combat a potentially fatal parasitic disease.

The eight students from the Royal Free and Guys and St Thomas's Hospitals are going to Belize to collect 750 sand flies.

They hope to find the species responsible for transmitting the disease Leishmania braziliensis, which is endemic throughout South and Central America. A fly bite can lead to severe facial disfigurement and even death.

Polly King, a fourth-year student at the Royal Free Hospital school of medicine who is leading the expedition, said a South American child, known as Boy David, was bitten by one of the flies.

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"He had his nose and mouth destroyed by the disease but was adopted by a plastic surgeon who reconstructed his face," she said.

"It's not known which particular species of sand fly carries the parasite, so the main part of the project is trying to identify the carrier for the disease."

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A student project last year collected 250 sand flies, but the team discovered they had been given misleading information on the disease in Belize, and were not in the worst-affected area. These flies have been catalogued by species at the Natural History Museum in London and are due to be analysed at Cambridge University. But Ms King said the chances of finding an infected fly were very low.

This year's expedition is going to a different part of the country, armed with ultraviolet light traps: When a fly lands on the light, a fan sucks it into a filter. The students are also using the less technological method of putting lights under bedsheets, and then removing the flies with suckers.

"They are less than two millimetres long, so we will have a microscope out in the field to check whether we have caught the right flies. They are quite distinctive, since their wings are at 90 degrees to their body," Ms King said.

"Then they will be sexed and speciated and have DNA tests to see if they're infected."

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The expedition is not directly linked to the students' academic work, and they are still Pounds 1,000 short of their Pounds 4,200 budget, despite a series of fundraising events including a sponsored walk of London's bridges, dressed as sand flies.

"It will not stop the expedition, but it will be more difficult to process the flies when we get back," Ms King said.