Transmission risk of Lyme disease and implications for tick management.

Transmission risk of Lyme disease at a site can be estimated using the probability of exposure (P1 = probability of being bitten by at least one infected tick); P1 = 1 - (1 - kt)n, where n = number of tick bites per person and kt = spirochete prevalence in questing ticks. This probability is more directly related to the likelihood of acquiring Lyme disease than the standard measure of transmission risk (the number of infected ticks per sample) and allows for direct consideration of the level of tick/human contact (by varying n) in assessing exposure risk and designing management strategies. Projections predict that interventions that lower tick abundance or spirochete prevalence do not necessarily result in equivalent declines in human exposure risk. Management interventions are predicted to have greatest success at lowering disease incidence in humans when tick abundance and/or pathogen prevalence in questing ticks are initially low (e.g., for ticks in residential lawns or for low-prevalence diseases). These techniques are predicted to be less effective at lowering disease incidence in people engaged in high-risk activities at sites with high tick abundance and pathogen prevalence, such as wooded sites in highly endemic areas.