The ironic result was that Lyme disease was not considered to have occurred in Massachusetts until the case criteria were changed in 1982. This confusion resulted in an inordinate number of diagnoses of spider-bite during the 1970s, before these skin lesions were correctly attributed to the bites of spirochete-infected Ixodes ticks.

Once deer and infected ticks become well established in a populated site, the risk of human Lyme disease increases rapidly. Such was the case in the New York vacation communities on Fire Island, which became notorious foci of Lyme disease during the late 1970s, registering an annual incidence of about 1 percent (Hanrahan et al., 1984). A similar rise in cases occurred between 1975 and 1983 on Great Island, Massachusetts, where the annual incidence came to exceed 5 percent (Steere et al., 1986). An epidemic outbreak in Ipswich, Massachusetts, began in 1980, the year after Ixodes ticks were first discovered on the carcasses of deer. By 1986, the annual incidence of Lyme disease in that community came to exceed 10 percent (Lastavica et al., 1989). Similarly explosive growth in the trend of human cases of Lyme disease has been noted elsewhere, particularly in parts of New York, New Jersey, Pennsylvania, Wisconsin, and Minnesota.

FIGURE 2-4 Distribution of Lyme disease in the United States, 1991.

SOURCE: D. Dennis, Division of Vector-Borne Infectious Diseases, Centers for Disease Control.