Occupational Health & Safety

Lyme Disease

(Lyme Borreliosis, Tickborne Meningopolyneuritis)

Lyme disease (PDF) is a multisystemic disorder associated with infection with a spirochete, Borrelia burgdorferi. The organism is transmitted by ticks of the genus Ixodes. Lyme disease, initially called Lyme arthritis, gained notoriety in the United States in 1975, when first described as an infectious disease while investigation was being conducted on an apparent cluster of cases of juvenile rheumatoid arthritis. After isolation of the spirochete, its similarity to erythema chronicum migrans (ECM), a clinical entity associated with a bulls-eye-like rash recognized in Europe, became more apparent. The disorder is now generally called either Lyme disease in North America or Lyme borreliosis in other regions.

Lyme disease is most the most frequently reported tick-associated disease in North America. More than 50,000 cases have been reported in the United States since 1979. The disease is considered endemic in more than 23 states in the United States and in southeastern Ontario, Canada.

The disease is characterized by a distinctive skin lesion, systemic symptoms and neurologic, rheumatologic and cardiac involvement that occur in varying combinations over a period of months to years. The early symptoms are intermittent and changing. The illness typically begins in the summer, and the first manifestation in about 90% of patients appears as a red macule or papule that expands slowly in an annular manner, often with central clearing. The distinctive skin lesion is called "erythema migrans" (EM; formerly "erythema chronicum migrans"). EM may be single or multiple. To be considered significant for case surveillance purposes, the EM lesion must reach 5 cm. in diameter. With or without EM, early systemic manifestations may include malaise, fatigue, fever, headache, stiff neck, myalgia, migratory arthralgias and/or lymphadenopathy, all of which may last several weeks or more in untreated patients.

WIthin weeks to months after onset of the EM lesion, neurologic abnormalities, including facial palsy, chorea, cerebellar ataxia, radiculoneuritis, myelitis, and encephalitis, may develop. Symptoms fluctuate, may last for months and may become chronic. Weeks to years after onset, intermittent episodes of swelling and pain in large joints, especially the knees, may develop and recur for several years.

Borrelia burgdorferi has been isolated from numerous species of vertebrates; however the ability of these species to serve as reservoirs of the spirochete is variable. The white-footed mouse is the primary reservoir of Borrelia burgdorferi in endemic areas of northeastern United States. The mice acquire the spirochete when used as hosts by infected nymphal Ixodes scapularis ticks. The mice remain persistently infected through the spring and summer, which facilitates infection of feeding larvae during late summer. White-footed mice have a prominent role as a host for immature Ixodes scapularis ticks, and efficiently transfer the spirochete to attached ticks. Deer mice, chipmunks, voles, house mice, Norway rats, and rabbits can also transfer infection to attached ticks, but with less efficiency.

In the southern United States, there is a greater diversity of alternative hosts for Ixodes scapularis, including reptiles. Some reptile species can maintain Borrelia burgdorferi infection and transmit the spirochete to attached ticks. White-tailed deer serve as the primary host of adult Ixodes scapularis, and the distribution of this important vector is tied to the distribution of the white-tailed deer. Studies have cast doubt on the role of white-tailed deer as potential reservoirs of the spirochete.

Birds have been found to be infected with the spirochete; however, their role as potential reservoirs is poorly defined. Studies with the cat bird and the European black bird indicated that these species do not efficiently transfer the spirochetes to attached ticks, which negates their potential role as reservoirs. Infected ticks that attach to birds can be transported long distances on the birds. In this manner, bird migrations may have a role in the expansion of the geographic range of the spirochete by depositing infected ticks in nonendemic areas.

The risk of Borrelia infections for human beings that engage in outdoor activities in endemic areas can be minimized by adhering to simple precautions that can be taken for personal protection: avoid tick-infested areas; examine yourself frequently for ticks and remove them before they attach; remove attached ticks as soon after attachment as possible; wear long sleeves and pants when entering tick-infested areas; use a tick repellent or acaracide as directed by the manufacturer; and be aware of the clinical signs of the disease. Seek medical attention if you develop fever, rash, or other signs of disease after visiting a tick-infested area.

Ticks are negatively geotropic, and move upward when they find a host. An additional step taken by many field researchers takes advantage of this behavior and helps recognize exposure to ticks before they attach to the lower extremities. Taping (with heavy duct tape) the ends of pants to shoes or boots over socks produces a barrier that requires ticks to move upward on the outside of pants rather than the inside. This facilitates easier visualization of ticks while walking in tick-infested areas.

Lyme disease ia a wildlife-associated zoonosis; however, the wildlife associated with maintenance of Ixodes tick populations are common inhabitants of suburban settings. Changing land-use patterns have facilitated reforestation of agricultural land throughout North America. Reforestation has supported repopulation of white-tailed deer herds and has contributed to the spread of the deer tick and the disease. Residential construction in these reforested areas has heightened human exposure to wildlife-associated zoonoses. Indeed, backyard exposure to Ixodes scapularis frequently is associated with Lyme disease cases in endemic areas.