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This article waslast modified on 24 November 2020.

Lyme disease is an infection caused by a spiral bacterium, Borrelia burgdorferi, carried by a tick the size of the head of a pin. The tick is found in woods and heathland areas where it infests small animals and birds. People bitten by an infected tick which is not removed within a day or two may develop Lyme disease. An expanding rash called erythema migrans appears at the site of the bite within 3 to 30 days in a large proportion of those infected. Some develop flu-like symptoms with aching joints and muscles. The disease can later affect the nervous system, joints and other body systems.

The best defences against Lyme disease are wearing protective clothing, using an insect repellent, and checking for (and carefully removing) ticks at regular intervals. Tests that can help diagnose Lyme disease detect antibodies that the body develops against the Borrelia burgdorferi bacterium. They appear some weeks after being bitten, so the tests may be negative if done too early and may need to be repeated a few weeks later.

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About Lyme Disease
  • Symptoms

    The first symptom of Lyme disease in 80% of those infected with Borrelia burgdorferi is a rash that appears a few days to a month after a tick bite that is usually painless. (In Europe, a third of those with the rash do not recollect a bite.) The characteristic rash, called erythema migrans, is flat, round or oval, pink or red and typically grows outward from the bite site for several weeks. It is usually becomes larger than 5 cm across and can be as large as 1 metre. Most develop a central clearing area and begin to look like a "bulls-eye." Some people may develop multiple red rashes and others may not have, or remember having, a rash. Flu-like symptoms sometimes develop with fever, headache, tiredness, nausea, vomiting and aching joints and muscles.

    If left untreated, additional symptoms may emerge after several weeks or months:

    • Nervous system symptoms in up to 15%, including temporary paralysis of facial muscles on one or both sides, numbness and pain in the limbs, difficulty concentrating and poor memory. A few develop meningitis with headache, neck stiffness and sensitivity to light
    • Heart symptoms including fainting or chest pain
    • Joint symptoms of arthritis with repeated brief attacks of joint swelling in one or more large joints, often the knee.

    In a minority of untreated patients, persistent nervous system or joint disorders may develop many years after infection.

  • Tests

    Laboratory tests are unnecessary if you have had a tick bite that becomes red and swollen when the tick is still attached or shortly after it drops off or is removed, but you have no other symptoms. This is a tick hypersensitivity reaction, not Lyme disease.

    If you develop the characteristic spreading rash of Lyme disease (erythema migrans) 3 to 30 days after a tick bite or possible exposure to ticks, your GP is highly likely to make a clinical diagnosis. You will be treated with antibiotics without having had any laboratory tests, and should make a complete recovery.

    However, if you see your GP without a characteristic rash but with other symptoms that occur in early or later Lyme disease, the information that you have had a tick bite or possible exposure to ticks may be very helpful.

    The first test done is an enzyme-linked immunosorbent assay (ELISA) blood test for antibodies to Borrelia burgdorferi. The antibodies take time to develop so the test may not be requested until a few weeks after the onset of symptoms. Although it is a sensitive test, it has a high false positive rate, giving positive results in glandular fever, rheumatoid arthritis and other autoimmune conditions for example.

    If the initial ELISA result is borderline or positive, the laboratory will retest the same sample using a more specific test, a Western blot, to confirm the diagnosis.

    Another specific test, the polymerase chain reaction (PCR), detects the DNA of Borrelia burgdorferi. It is used to confirm the presence of the bacterium in joint fluid in Lyme arthritis and in cerebrospinal fluid (CSF) in Lyme meningitis.

  • Prevention and Treatment

    There is no vaccine to prevent Lyme disease, so it is important to take precautions to reduce the risk of becoming infected when going to wooded or grassy areas, particularly in the spring and early summer. When on holiday, remember that the risk is greater in other European countries and in the US than in the UK.

    Wear a long-sleeved top and tuck your trousers into your socks. Ticks are easier to spot if your clothing is a light colour. Use an insect repellent. At the end of the day inspect your skin and that of your children for ticks, particularly the scalp, armpits, groin, back of the knees and the waist band area. Remember to check any pet, too. 

    Image of a tick
    Source: Photo from spex photostream


    To remove a tick, carefully grasp it gently by the head part (not the body) as near your skin as possible, preferably with fine-toothed pointed tweezers, and lift it straight out. If you have been bitten, don’t become over anxious: only a minority of ticks in the UK are infected, and only those infected that are left on the skin for more than a day are likely to pass on the infection. However, if a spreading rash or symptoms of flu appear in two to four weeks, see you GP straight away.

    Antibiotics taken by mouth for two to four weeks are used to treat Lyme disease whether it is diagnosed early or at a later stage. If symptoms are particularly severe, or if there is arthritis or meningitis, the antibiotic is given into a vein in hospital. Most people make a complete recovery. However, if the disease has reached a late stage before treatment, symptoms including tiredness and joint and muscle pain may persist, sometimes for 6 months or longer.