Epidemiologic studies of hard tick-associated illness in the United States
Date
2009
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Abstract
This dissertation describes three epidemiologic studies of hard tick-associated illness in the United States. The first is the prospective health assessment of Fort Campbell, Kentucky patrons bitten by ticks during 2004-2006. The study was designed to determine the frequency, clinical characteristics, and etiology of Amblyomma americanum-associated illness and to identify associated risk factors. Amblyomma americanum is an aggressive human biting tick associated with a Lyme disease-like illness of unknown etiology. Study findings suggested that a variety of symptoms were temporally associated with tick bite but data provided no clear evidence that symptoms were caused by an infectious process. Removing ticks by hand or being bitten on a limb may have been risk factors for illness. The second examines 248,074 cases of Lyme disease reported to the Centers for Disease Control during 1992-2006 using descriptive and inferential statistics. In the United States, Lyme disease is caused by Borrelia burgdorferi sensu stricto, a spirochete transmitted to humans by infected Ixodes scapularis and I. pacificus ticks. During the 15-year study period, the number of cases reported annually increased 101% and the majority of cases occurred in northeastern and north-central states. An increasing trend in the number of counties reporting at least one case annually was observed in Minnesota, Rhode Island, and Wisconsin. A disproportionate increasing trend in reported cases was observed in children and young males compared with other demographic groups. The third study is a pilot ecologic analysis of human social or economic factors affecting, or resulting from, Lyme disease emergence. The objectives were to identify space-time clusters of increased Lyme disease risk and determine if risk could be partially explained using existing data on environment, socioeconomics, and healthcare. As expected, Ixodes tick distribution was a significant predictor of counties with increased risk. Measures of socioeconomic status surfaced as predictors of ecologic risk, and it appeared that persons of high SES lived where ticks were reported in northeastern states and persons of low SES lived where ticks were reported in the north-central states.
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Subject
Amblyomma americanum
Borrelia burgdorferi
Ixodes scapularis
Lyme disease
tick-borne diseases
epidemiology