Lyme disease

Lyme disease is caused by a spirochaete Borrelia burgdorferi, which has at least 11 different genomic species. It is a zoonosis of deer and other wild mammals. The syndrome was first recognized and named following an 'outbreak' of arthritis in the town of Lyme, Connecticut, in the mid-1970s. Since then the disease has increased in both incidence and detection: it is now known to be widespread in the USA, Europe, Russia and the Far East. Infection is transmitted from animal to man by ixodid ticks, and is most likely to occur in rural wooded areas in spring and early summer.

Clinical features

The first stage of the illness, which follows 7-10 days after infection, is characterized by the skin lesion, erythema migrans at the site of the tick bite. This is often accompanied by headache, fever, malaise, myalgia, arthralgia and lymphadenopathy. Many people have no further illness after this. A second stage may follow weeks or months later, when some patients develop neurological symptoms (meningoencephalitis, cranial or polyneuropathies), radiculopathies, cardiac problems (conduction disorders, myocarditis) or arthritis. These manifestations, which are often fluctuant and changing, usually resolve spontaneously over months or years. Some patients, however, develop chronic and persistent neurological disease (e.g. paraparesis) or rheumatological disease ('late Lyme disease'). Acrodermatitis chronica atrophicans, usually on the backs of the hands and feet can occur if the disease does not resolve spontaneously.

Diagnosis

The clinical features and epidemiological considerations are usually strongly suggestive. The diagnosis can only rarely be confirmed by isolation of the organisms from blood, skin lesions or CSF. IgM antibodies are detectable in the first month, and IgG antibodies are invariably present late in the disease. Commercial tests (ELISA, immunofluorescence, haemagglutination) are available but false positive results do occur. A genuine positive IgG may be a marker of previous exposure rather than of ongoing infection.

Management

Amoxicillin or doxycycline given early in the course of the disease shortens the duration of the illness in approximately 50% of patients. Late disease should be treated with 2-4 weeks of intravenous benzylpenicillin or ceftriaxone. However, treatment is unsatisfactory, and preventative measures are necessary. In tick-infested areas, repellents and protective clothing should be worn. Prompt removal of any tick is essential as infection is unlikely to take place until the tick has been attached for more than 48 hours. Ticks should be grasped with forceps near to the point of attachment to the skin and then withdrawn by gentle traction. Antibiotic prophylaxis following a tick bite is not usually justified, even in areas where Lyme disease is common. A vaccine was available but has recently been withdrawn.