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The Ecology of Lyme-Disease Risk

Complex interactions between seemingly unconnected phenomena determine risk of exposure to this expanding disease

Richard Ostfeld

Diagnosing the Disease

Figure 2. Lyme disease . . .Click to Enlarge Image

To the average physician, Lyme disease is suspected when a patient arrives at a clinic or hospital complaining of a strange bull’s-eye-shaped rash, known as erythema migrans, or EM, together with one or more flu-like symptoms, such as fever, chills, muscle aches or lethargy. The doctor will take a blood sample for laboratory confirmation, but will feel quite confident to make a diagnosis of Lyme disease after noting the telltale combination of symptoms, as well as the circumstances surrounding the infection. The patient will undoubtedly have been bitten by the black-legged tick Ixodes scapularis, formerly called the deer tick, or a close relative, which transferred to him or her the B. burgdorferi bacterium. Most likely, the doctor will prescribe an oral course of antibiotics and will duly report the case to the county or state health department, which will include it in the morbidity statistics for Lyme disease.

Figure 3. Bull's-eye-shaped rash . . .Click to Enlarge Image

Accurate diagnosis and effective treatment of Lyme disease is not always so straightforward, particularly in regions of the country newly invaded by the epidemic. In these regions, health-care professionals and the public need to be educated about the confusing and generalized symptoms, the generally poor, albeit growing, accuracy of lab tests and the efficacy of various antibiotic treatments. If Lyme disease is left untreated for some time, B. burgdorferi may persist in the patient's tissues and can migrate to the central and peripheral nervous system or to joints and cause more-severe late-stage symptoms, which include arthritis and neurological disorders, such as dizziness, memory loss and disorientation. Vaccines that protect against Lyme disease are now being field-tested by pharmaceutical companies, but none has yet been approved by the Food and Drug Administration for public use. Even if an effective vaccine were certified and marketed, the primary means that individuals have of protecting themselves against the disease is avoiding the tick in the first place. To do that, ecologists are trying to understand the natural history of Lyme disease and the life history of the black-legged tick.

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