Lyme disease is an illness which can affect the skin and in some patients the nervous system, joints or heart. It is caused by a spiral shaped bacterium called Borrelia burgdorferi (B burgdorferi) Man and other animals can be infected with the organism but not everyone develops symptoms. Lyme disease was so named because a cluster of cases of arthritis was observed in children in Lyme, Connecticut in the USA in 1975. This was originally thought to be due to rheumatoid arthritis but subsequent investigation showed the condition to be an infectious disease. However, this is not a new disease; it had been known in Europe under a variety of names since the beginning of the 20th century. Lyme disease is common in the United States and Scandinavia. Other countries in Western and Eastern Europe, the former Soviet Union, and Japan, China, and Australia have all reported cases. It is not a common illness in the UK, with less than 200 cases per year being reported in England and Wales in recent years. There is no evidence that the disease is increasing in the UK but recently it has become more frequently recognised because awareness of it has increased in the general public and the medical profession, and blood tests which can help in diagnosis are now available.
B burgdorferi is transmitted by the bite of an infected tick. Ticks are tiny, spider-like creatures which are found in woodland, moorland and other grassy areas. They are blood-suckers and have a complicated life-cycle with three stages, larva, nymph and adult. The tick feeds once during each stage by taking blood from a host. Larvae and nymphs are very tiny and usually feed on small mammals such as field mice or voles, while adult ticks tend to feed on larger animals such as sheep, deer, or horses, and can reach the size of a coffee-bean after a feed. If ticks feed on an animal which is infected with B. burgdorferi they become infected and can pass on the organism to another animal when they feed again in a later stage of their life-cycle. In this way a reservoir of infection is maintained in animals. Man and domestic animals can act as a host for ticks at any stage of their life-cycle and may therefore also become infected. Clinical illness does not seem to occur in infected wild animals but occurs in humans and domestic animals.
Many infected people have no symptoms at all. Some patients develop a reddish-pink rash called erythema migrans, which spreads out from the site of a bite after three to thirty days. Patients may be feverish and have some enlargement of the lymph glands near to the site of the rash. They may also complain of aches and pains and feel very tired. The rash may spread to cover quite a large area of skin but it will gradually clear starting from the centre outwards, even if not treated with antibiotics. The rash usually fades after three to four weeks, although in some patients it may last much longer. Treatment shortens the duration of the rash, and should prevent later complications.
Much less frequently there may be nervous system complications such as facial palsy, which is a weakness or paralysis of muscles on one or both sides of the face. Other neurologic problems include mild meningitis, abnormal sensations on the skin (described by some patients as feeling like sunburn), and numbness, weakness or pains in different parts of the body. These complications may occur months or even years after the bite of an infected tick and some patients with these and other complications do not remember having been bitten or having had an erythema migrans rash earlier.
Lyme disease can occasionally trigger an arthritis which in most affected people will settle down after treatment, but sometimes it may be more prolonged and may recur at intervals. Lyme arthritis occurs more frequently in North America than in Europe and differences in the incidence of arthritis may be due to a genetic predisposition to arthritis in these patients. An abnormality of heart-beat rhythm may occur within a few weeks of the bite, but this is uncommon and responds well to treatment. Other complications are rare.
The illness can be difficult to diagnose if the patient and doctor are not aware that there has been exposure to infected ticks. This particularly applies to people who live in urban areas who may only have been exposed for a brief period during a holiday or even a day trip. Many people sustain tick bites but remain unaware of them because of the tick's tiny size.
The rash may appear quite shortly after a tick bite has occurred, but blood tests for Lyme disease will be negative for several weeks. The blood test detects antibodies to B. burgdorferi produced by the body in response to the infection, but they are not produced in detectable amounts for some weeks after infection has occurred. The rash usually has a characteristic appearance so the diagnosis can be made without a positive blood test, especially if there is known exposure to the risk of tick bites. Treatment with commonly used antibiotics such as amoxycillin or tetracycline is usually very effective in shortening the duration of the rash and preventing the development of later complications. Treatment is usually given for between 10 and 30 days, depending on the patient and the presence of complications.
Neurologic, arthritic and other complications may develop many weeks or months after the infection has occurred, by which time blood tests for antibodies to B. burgdorferi are almost always positive. Again it is important for the patient and doctor to be aware that there has been possible exposure to ticks, so that Lyme disease can be considered as a cause of the symptoms and appropriate blood tests performed. Effective treatment of the later complications of Lyme disease may require antibiotics to be given by injection for several weeks. Full recovery may take some time, especially if symptoms have been present for a long time.