Last updated at 14:43 02 May 2008

Most holidaymakers come home feeling refreshed and with some happy snaps to remember their trip by.

But what Alan Evans unwittingly brought back with him after two weeks in Gambia with his wife Karen was more like something from a horror movie - and left him under the surgeon's knife.

Days after he returned, on closer inspection of what he thought were six mosquito bites on his leg, he was terrified to see something wriggling under the surface of his skin.

And - look away now if you're squeamish - it turned out to be maggots.

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The bug hunter: Alan Evans looked at his bites under a magnifying glass... and saw something moving under his skin

Yesterday Mr Evans, 50, a petrol delivery driver, of Yatton, near Bristol, said: 'I started to feel really weak, as though something was sapping all the energy out of me.

'Then it felt like someone was stabbing me in the leg with a dagger.

'I was sure I could see something move under my skin and when I poked it, it went back down. At one point it looked like a crab's claw and I was petrified I had baby crabs growing inside me. It was terrifying.'

His doctor at first diagnosed a course of antibiotics to treat what he thought was a tropical infection.

It was only when Mr Evans, frustrated that the irritation had not cleared up, bought a magnifying glass to examine the bites that he realised the skin-crawling truth that something was inside him.

He was referred to hospital, where it was established he had been infected by bot fly, which lays its eggs under the skin and feasts on live human cells.

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What lies beneath: The botfly larvae in all their gory glory

Under a local anaesthetic, four live maggots were cut out and sent to a lab for testing. The other two maggots, already dead, were dressed with petroleum jelly and Mr Evans managed to squeeze their bodies out himself the following day.

He said: 'When I went to the doctors I got them to look at my leg through the magnifying glass for about ten minutes until they saw movement as well.

'When they got them out, it was really horrible to see them, but I was a relief at the same time that they were finally out of me.

'They think it was the bot fly. I was told there was a 1 in 15 million chance of getting this.'

Mrs Evans, 47, was bitten many times by mosquitos during the trip, but Mr Evans was only bitten on the last night.

He was later diagnosed with the rare disease myiasis, which is caused by parasitic larvae - more commonly called maggots - feasting on live cells of animals or humans and leaving painful boil-like sores.

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Unwanted souvenir: The bites he received in Gambia caused agonising, stinging pains in Mr Evans's leg

A mosquito will carry the bot fly eggs, and when it bites the skin, will drop the eggs and they burrow under the skin's surface.

They stay just below the surface to breathe, and the most common treatment is to cut off their air supply with vaseline - so they will crawl out.

Untreated, they can burrow too far down and need to be cut out before they develop into flies.

Contracting the condition is highly unlikely, and the only reported cases are from tropical areas, mainly Africa and South America.

Dr Ron Behrens of the London Hospital of Tropical Diseases sees two or three myiasis patients per month at his clinic, all of whom have returned from tropical areas.

He said: 'It can occur in anyone. A mosquito drops the bot fly's eggs onto the skin. The bot fly doesn't come into contact with the person, the mosquito does it, as a third party.

'The pupae then burrow under the skin - often the scalp, legs or groin area - and feed off it, but stay close to the surface so they can breathe.

'Flies can also lay their eggs on clothing hanging out to dry, so we recommend ironing it beforehand, if you're staying in a tropical area.

'They would have been growing bigger under this man's skin, which makes it very painful. After a couple of weeks they develop into flies, and are moving around - which is very unpleasant. But luckily it can be successfully treated.'

Mr and Mrs Evans were planning to return to Gambia later in the year but have been advised not to return in case Mr Evans contracts an infection.