It is a disease which affects almost any part of the body and produces a bafflingly wide range of symptoms, including skin lesions, meningitis, progressive muscular and joint pain, mood changes and behavioural problems. Doctors don't know how best to diagnose or treat it, and can't easily tell when it has been cured. Yet, left untreated, it can become incurable a lifelong debilitating illness characterised by neurological disorders, emotional and mental disorders, serious pain syndromes in the bones and muscles, and even fatal heart disease and respiratory failure.

Lyme disease, or Lyme borreliosis, is a blood borne disease first recognised in the US in 1975 after a mysterious outbreak of arthritis in 51 residents of the Atlantic seaside town of Lyme, Connecticut. Since then, reports of Lyme disease have increased dramatically in the US and western Europe, and it is now recognised as an important public health problem.

Suggestions that Lyme disease is overdiagnosed have caused an outcry from physicians who specialise in the disease. While this may have been so in the early days, genuine cases are growing year by year. In the US, the number of cases has doubled during 1992-1998 (MMWR, 2000; 49: 1-11) while the UK has shown an alarming fivefold increase from 0.06/100,000 during 1986-1992 to 0.32/100,000 since 1996.

The infection is due to Borrelia burgdorferi, a spiral shaped bacterium known as a spirochaete, spread by the bite of ticks of the genus Ixodes, which normally live off the blood of the white footed mouse, white tailed deer, birds and other mammals, including dogs and cats. Blood transfusions may also be a means of infection though debate rages as to how high the risk is (see box).

Ixodes ticks are no bigger than a pinhead in the larval and nymphal stages, and adults are about the size of a poppyseed. The ticks transmit Lyme disease to humans mostly during the nymph stage, probably because they have not yet developed their stronger preference for mice and deer. Because of their small size, the nymphs are rarely noticed, and so have ample time to feed and transmit infection (usually after two or more days of feeding).

Larvae rarely carry the infection and, although adult ticks can transmit the disease, they are more likely to be discovered and removed. The adults are also more active during the cooler months of the year, when human outdoor activity is limited.

Lyme disease is largely a product of environmental mismanagement, deforestation and reforestation, and squeezing of wildlife and humans into smaller and smaller designated spaces, such as deer parks and nature reserves (see Garrett L, The Coming Plague, Penguin, 1994). Most humans with Lyme disease live in wooded areas inhabited by common wild animals such as deer, squirrels, chipmunks with an absence of natural predators such as wolves, cougars and coyotes that keep these animals in check. Scrubby areas near the seaside are also common sites for Lyme carrying ticks.

Difficulty in diagnosis

Immunologists view the disease as a simple infection, leading to diagnostic tests that look for immunological factors, such as antibodies in the blood and cerebrospinal fluid (CSF).

However, reviews of such antibody detecting tests have revealed their generally dismal performance and considerable interlaboratory variability (J Infect Dis, 1987; 155: 1325-7; J Am Med Assoc, 1992; 268: 891- 5). Indeed, it is believed that the standard two test approach to diagnosis using either an enzyme linked immunosorbent assay (ELISA) or immunofluorescent assay (IFA), followed by Western immunoblot testing in positive or equivocal specimens, can miss up to 87 per cent of infected patients.