LymSiM simulates the population dynamics of the blacklegged tick, Ixodes scapularis, and the dynamics of transmission of the Lyme disease agent, Borrelia burgdorferi, among ticks and vertebrate hosts. LymSiM models the effects of ambient temperature, saturation deficit, precipitation, habitat type, and host type and density on tick populations.

The model accounts for epidemiological parameters, including host and tick infectivity, transovarial and transstadial transmission, such that the model realistically simulates the transmission of the Lyme disease spirochete between vector ticks and vertebrate hosts. The software features a dynamic life table model of Ixodes scapularis with a weekly time step; rates of development, survival, fecundity, and host finding are based on weather or other environmental variables and vary with time. The relationships used were based on the literature and unpublished field studies.

Required inputs are:

1. Proportions of forested, meadow, and ecotone;
2. Weekly average temperature, rainfall total, relative humidity, and saturation deficit;
3. Density of the four to six types of hosts.

A principal use of LymSiM has been to simulate and optimize the effects of management technologies on populations of tick vector, Ixodes scapularis, and Borrelia burgdorferi in eastern North America. The model was used to evaluate area-wide acaricide treatments, acaricide self-treatment of white-footed mice and white-tailed deer, vegetation reduction, and white-tailed deer density reduction. Simulations demonstrated that area-wide acaricide, vegetation reduction, or a combination of these technologies would be useful for short-term seasonal management of ticks and disease in small recreational or residential sites.

Moreover, acaricide self-treatment of deer appears to be the most cost-effective technology for use in long-term management programs in large areas. Simulation results also suggested that deer density reduction should be considered as a management strategy component. Finally, the model was used to develop integrated management strategies for operational tick and tick-borne disease control programs.

Based on the previous studies, the U.S. Centers for Disease Control and Prevention used LymSiM to evaluate various Lyme disease control techniques as a function of various degrees of compliance by the public involved in anti-tick measures. This assessment comparing the effectiveness of alternative community-based prevention strategies illuminates the limitations and distributive effects of interventions and helped clarify the actual available prevention options for community residents.

Dana A. Focks

Infectious Disease Analysis, P.O. Box 12852, Gainesville, FL 32604 USA; Tel: 352.375.3520; Fax: 352.372.1838; e-mail: dafocks@id-analysis.com.

Hayes, E.B., G.O. Maupin, G.A. Mount, and J. Piesman. 1999. Assessing the prevention effectiveness of local Lyme disease control. J Public Health Manag Pract 5(3):84-92.

Mount, G.A., D.G. Haile, and E. Daniels. 1997. Simulation of management strategies for the blacklegged tick (Acari: Ixodidae) and the Lyme disease spirochete, Borrelia burgdorferi. J Med Entomol 34(6):672-663.