Lyme disease is a tickborne illness that results from infection with members of the Borrelia burgdorferi sensu lato complex. These organisms are maintained in wild animals, but they can affect humans and some species of domesticated animals. Lyme disease was first recognized in the 1970s, when a cluster of juvenile arthritis cases was investigated in the U.S., but its symptoms can be found in European historical records as far back as the early 20th century. This disease has also been detected in Australia, parts of Asia, the province of Ontario, Canada, and recently, the Amazon region of Brazil. Lyme disease in people is readily cured with antibiotics during the initial stage of the illness, when an unusual rash often aids disease recognition. However, people whose infections remain untreated sometimes develop chronic arthritis, neurological signs and other syndromes. Lyme disease in domesticated animals is still poorly understood, and no distinctive rash seems to occur. The illness is best characterized in the dog, where arthritis and nephropathy appear to be the most common sequelae. Clinical signs attributed to Lyme disease have also been reported in other species including horses and cattle.