Lyme disease - Causes of Lyme disease

Lyme disease is caused by the Borrelia burgdorferi bacteria. The bacteria are present in the blood of many different animals including mice, deer, pheasants and blackbirds.

If a tick (a tiny arachnid) bites an animal that has the bacteria, the tick can also become infected. The tick can then transfer the bacteria to a human by biting them and feeding on their blood.

Ticks are very small and their bites are not painful, so you may not realise you have one attached to your skin. However, there is a higher risk you will become infected if the tick remains attached to your skin for more than 24 hours.

Once infected, the bacteria moves slowly through your skin into your blood and lymphatic system. The lymphatic system helps fight infection and is made up of a series of vessels (channels) and glands (lymph nodes).

Left untreated, the bacteria that causes Lyme disease can damage the joints and the nervous system, leading to later symptoms of Lyme disease.

Where are ticks found?

Ticks can be found in any areas with deep or overgrown vegetation where they have access to animals to feed on.

Although this means they are most common in woodland and heath areas, they may also be found in gardens or parks where this kind of vegetation exists.

Cases of Lyme disease have been reported throughout the UK, but the infection is most commonly acquired in the southern counties of England. Around 15% of infections occur abroad.

Groups at risk

The groups most at risk of getting Lyme disease include those who work in woodland and heath areas and those who take part in activities in these areas. For example:

• hikers
• campers
• farmers
• forestry workers
• soldiers
• gamekeepers

Most tick bites occur in late spring, early summer and autumn because these are the times of year when most people take part in outdoor activities, such as hiking and camping.

Read more about preventing Lyme disease.