Entomologic and Demographic Correlates of Anti-Tick Saliva Antibody in a Prospective Study of Tick Bite Subjects in Westchester County, New York

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  • Department of Environmental Health Sciences, Division of Occupational Health, Department of Immunology and Infectious Diseases, Johns Hopkins University School of Hygiene and Public Health, Department of Medicine, Division of Infectious Diseases, Department of Community and Preventive Medicine, Medical Entomology Laboratory, New York Medical College, Baltimore, Maryland
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We measured anti-tick saliva antibody (ATSA) by enzyme-linked immunosorbent assay using whole sonicated Ixodes dammini salivary glands as antigen in subjects with 1) a recent and confirmed I. dammini (n = 100) or Dermacentor variabilis bite (n = 3), 2) erythema migrans (n = 15), 3) late-stage Lyme disease (n = 4), and 4) normal controls without a history of tick bites (n = 5). Tick bite subjects had three ATSA determinations over approximately six weeks. On the first ATSA measurement at a mean ± SD of 18.5 ± 19.8 hr after removal of the tick, the subjects bitten by I. dammini had a mean ATSA optical density value (95% confidence interval [CI]) of 0.264 (0.223, 0.305); the corresponding value in controls was 0.142 (0.115, 0.169). There was no consistent change in ATSA levels in individuals with time. Multiple linear regression indicated that tick engorgement (P < 0.01), subject age (higher ATSA with increasing age; P = 0.01), and subject sex (females > males; P = 0.03) were all independent predictors of ATSA levels. Logistic regression revealed that a bite by I. dammini that became engorged (defined as an engorgement index ≥ 3.4) was a risk factor for ATSA seropositivity (odds ratio [95% CI] = 6.2 [1.7, 21.8]). Finally, the ATSA test had a sensitivity of 0.81 and a specificity of 0.56 for a bite by I. dammini that became engorged. Overall, the data are further evidence that ATSA is a biologic marker of tick exposure, in that the engorgement index, a surrogate for tick saliva dose, was the strongest independent predictor of antibody response.