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Current State of Knowledge in Washington
Despite surveillance efforts, relatively little is known about the ecology and epidemiology of Lyme disease in Washington. Although 1 to 2 percent of I. pacificus ticks tested in California and Oregon have been shown to be infected with B. burgdorferi, similar studies have not been performed in Washington. One case report from Redmond documented an apparent case of Lyme disease following a bite from another Ixodes species, I. angustus. |
Several factors hinder our understanding of the incidence and prevalence of Lyme disease in Washington residents. Exposure data cannot always be obtained. People are often unaware of tick bites. Because symptom onset occurs several days to weeks after the tick bite, patients may not recall the details of the exposure. Once the patient becomes symptomatic, the only potential pathognomonic physical finding is erythema migrans, but this lesion can mimic other rashes. Furthermore, patients often see their physician after the lesion has resolved, limiting the clinician to a verbal description of the rash. No other physical finding is diagnostic and, unfortunately, with the exception of a culture, a laboratory gold standard does not exist. As noted above, attempting to culture B. burgdorferi is a low-yield, high cost, and time consuming endeavor. Despite many unanswered questions, enough evidence exists to suggest that the incidence of Lyme disease is low in Washington. Exposures occur mainly west of the Cascade Mountains, consistent with the distribution of Ixodes ticks. Other tick-borne infections such as relapsing fever and tick paralysis are more common east of the Cascades. |