Visitors to the countryside are being warned of an increased risk of contracting Lyme disease, amid a sharp rise in the tick population.

With the warm spring bringing out walkers, cyclists and riders. the Health Protection Agency is advising people to take precautions against tick bites particularly when visiting woods, heaths and moorland – and even suburban parks.

In England and Wales the number of diagnoses of Lyme disease rose to 684 last year. In Scotland reported cases have risen tenfold in a decade, last year doubling to 177.

The disease starts with an expanding, “bull’s-eye” rash and flu-like symptoms that are treated with antibiotics. If early warning signs go undetected, the bacteria may cause complications such as arthritis, meningitis, paralysis of facial muscles, depression and memory problems.

Britain’s milder winters, and wetter, warmer weather generally, provide an ideal breeding-ground for the tiny, spiderlike ticks – which have also had a devastating impact on grouse numbers. Last December was the warmest in Britain for 18 years and 2006 the warmest year on record.

Ixodes ricinus, the sheep tick, can live on most warm-blooded mammals, and attaches itself to humans by burying a probe into the skin to suck blood.

Ticks begin life as black insects the size of a pinhead, but swell to the size of a pea after gorging on blood, before turning grey and dropping off their host.

Their bite is painless, and they are so small that one might not know they are there. The insects cannot fly, but wait in grass, heather, bracken and trees for a host to brush past.

It is not known definitively how may ticks carry Lyme disease, Lyme borreliosis, but some experts estimate that it could be as high as one in three. Oxford University’s zoology department is charting hotspots.

John Cowden, an epidemiologist at Health Protection Scotland, said that there could be even more cases of Lyme disease than was known. “It could be down to milder weather, global warming, or the fact that more people are out walking.

“There is not a lot we can do other than advise people to be careful. We cannot get Lyme disease out of the environment. It is quite simply up to individuals to avoid catching it.”

Infestations used to be confined to late spring and summer, but the parasites are now continually active in some areas.

It is widely held that a tick must be attached for 24 hours to pass on Lyme disease, so removing it quickly is crucial. The disease then has a three-week incubation period.

Wearing long-sleeved tops and trousers, and shoes rather than open sandals, can help to prevent bites.

Ramblers Scotland said that the risk of contracting the disease was small. Helen Todd, of the organisation, said: “Lyme disease is serious, but I am a walker and in the past ten years I have had about four ticks.” Known Lyme disease areas are the Highlands, the Yorkshire Moors, the Lake District, Thetford Forest, the New Forest, Berkshire, Wiltshire, the South Downs and Exmoor.

Plenty to grouse about

— Scotland’s commercial grouse moors, which rely on seasonal shooting parties, have been hit hard by the sharp rise in the tick population

— Ticks infect grouse chicks with a virus called louping ill. It is fatal in 80 per cent of cases

— In the past 20 years the number of grouse chicks infested with ticks has risen from 4 per cent to more than 90 per cent

— The Game Conservancy Trust is doing trials in the Highlands whereby sheep are given treatments that attract ticks and kill the insects when they bite

— Highland estates have also taken steps to cull wild deer in a effort to reduce the number of potential tick “hosts” available

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