Lyme disease is caused by a bacteria, called Borrelia burgdorferi, and is transmitted to humans through the bites of a tick.
The ticks are found either on animals such as deer and mice, or they jump onto the human when they brush past them in tall grass, shrubs or low trees.
America, particularly the forested areas of New England, has the most cases of Lyme disease - here the numbers of those infected run into hundreds of thousands each year.
Russia is also quite badly affected. But there are also cases of Lyme disease in the UK. Doctors usually see a few hundred cases of it each year.
And recent climate changes have been blamed for an increase in the infection.
There are a variety of symptoms linked to Lyme disease. The first is an expanding rash or bruise which starts at the bite mark, usually a week after the person has been bitten.
It can appear as either a single red blotch, or as a "bullseye" shape with a widening ring around its central point.
The mark can feel warm to the touch, but might not itch or cause pain.
After the rash appears sufferers may also start to suffer joint pains, fever, fatigue, stiff neck and facial paralysis or tingling as the bacteria starts to spread around the body.
More serious symptoms can include severe headaches, painful arthritis, joint swelling and heart problems.
Some patients even suffer mental disorders such as short term memory loss and difficulty concentrating.
But if the disease is caught early enough it can be treated with antibiotics, although later stage Lyme does not respond as well.
Anyone in an area where Lyme disease is thought to be prevalent should check themselves regularly to ensure that they have not been bitten.
Ticks can attach themselves anywhere on the body, but prefer creases like the armpit, groin or back of the knee.
Walkers should wear light coloured clothing and gardeners' light gloves, so they can see the ticks.
The ticks spread their disease slowly, so the quicker they are spotted the less chance there is of someone becoming infected.
The best way to remove a tick is by tweezers, although you should be careful to pull the tick out directly without jerking or twisting it. Antiseptic should then be put on the wound.