Lyme disease

What is Lyme disease?

Lyme disease is an infection caused by Borrelia burgdorferi, a type of bacteria called a spirochaete. Humans and animals are infected with the bacteria through tick bites on the skin. Infected Ixodes ticks are often found on deer. The disease is common in parts of the United States but may also exist throughout much of the world. In New Zealand, cases have only been reported in people that have recently travelled from an endemic area.

What happens after a tick bite?

Several things can happen after being bitten by an infected tick.

• The body's defence mechanisms can overwhelm and eliminate the infecting bacteria.
• The bacteria can remain localised at the site of the bite and cause a localised skin infection.
• The bacteria may disseminate via the blood and lymphatic system to other organs and cause a multisystem inflammatory disease.

Erythema chronicum migrans

Ixodes tick

What are the signs and symptoms?

Although Lyme disease can affect any part of the body, it appears to most often affect the skin, heart, central nervous system, joints and eyes. The disease can basically be divided into 3 stages according to the extent of infection. In individual patients there is no rigid cut-off between each stage.

Diagnosis of Lyme disease

It is important to get early diagnosis if you think you may have Lyme disease. Diagnosis can be made on the presence of erythema migrans and other symptoms, plus the evidence of a tick bite. Laboratory tests are usually not performed within the first month after initial infection, as these can be unreliable.

Undetected or ignored early symptoms may be followed by more severe symptoms weeks, months or even years after the initial infection. Certain laboratory tests are then recommended to confirm diagnosis, but can be misleading.

• Antibody titres to B burgdorferi using enzyme-linked immunoassay (ELISA) or immunofluorescent assay.
• A positive result should be confirmed by Western immunoblot
• Skin biopsy: histology is often non-specific but the skin can be cultured for the organism.

What treatment is available?

Localised or early Lyme disease generally responds well to appropriate antibiotics. Full cure is usually achieved if the disease is diagnosed and treated promptly, but the cure rate decreases the longer treatment is delayed. The choice of antibiotic depends on bacterial sensitivity. Antibiotics used include, amoxicillin, doxycycline, azithromycin, cefuroxime, erythromycin, penicillin VK and cetriaxone. The route of administration and the duration of course is still under debate and being defined. Current duration of treatment is somewhere between 10-30 days. Late stage Lyme disease should be treated with intravenous antibiotics.