Lyme Disease

Organism Borrelia burgdorferi, B. garinii and B. afzelii.

Clinical features The herald sign is an annular expanding erythematous skin lesion, called erythematous migrans (EM), often accompanied by fever, muscle pain, arthral-gia and signs of meningeal irritation. Infection may develop over weeks or months into aseptic meningitis, encephalitis, peripheral nerve signs, cardiac irregularities and polyarthritis.

Diagnosis is mainly clinical, the EM lesion exceeding 5 cm, aided by serological tests, more useful in the later stages of the disease.

Transmission is from the bite of an infected deer tick, Ixodes scapularis or I. pacificus, in North America or sheep tick I. ricinus in Europe. In Asia, I. persulcatus is the vector. The reservoir of infection is in the tick, which can transmit the Borrelia transova-rially. Adult ticks largely feed on deer (sheep in Europe), while the nymphal stage is responsible for transmitting the infection to humans and other animals, such as dogs, which will often develop similar symptoms to humans.

Incubation period 3-32 days (mean 7-10 days).

Period of communicability Not transmitted from person to person.

Occurrence and distribution Found in well-defined areas of USA and Canada, largely related to the deer population. Limited range in Europe, Russia, China and Japan. Foci of infection can be delineated by looking for the vector tick.

Control and prevention are similar to other tick-borne diseases mentioned above with the use of repellents and insecticide-treated clothing when passing through known infected areas. Since transmission of infection takes in excess of 24 h after the tick has attached, careful search of the body should be made after walking through countryside. The nymphal stage is the main transmitter to humans so small black spots should be looked for, possibly with the aid of a lens (see Fig. 16.4).

A vaccine has been developed against lyme disease in North America, but is not effective in other parts of the world. It is only useful for persons at constant risk of infection, such as game wardens or camp attendants, but other precautionary measures should also be taken.

Treatment is effective with doxycycline or amoxicillin in the early EM stage of the disease. In the late arthritic, cardiac or neurological stage of the disease, treatment is with benzylpenicillin or ceftriaxone for up to 21 days.

Surveillance Infected areas should be delineated and warning signs posted.

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