SIMULATION OF BLACKLEGGED TICK (ACARI, IXODIDAE) POPULATION-DYNAMICS AND TRANSMISSION OF BORRELIA-BURGDORFERI

A model (LYMESIM) was developed for computer simulation of blacklegged tick, Ixodes scapularis Say, population dynamics and transmission of the Lyme disease agent, Borrelia burgdorferi Johnson, Schmid, Hyde, St eigenwalt & Brenner. LYMESIM simulates the effects of ambient temperat ure, saturation deficit, precipitation, habitat type, and host type an d density on tick populations. Epidemiological parameters including ho st infectivity, tick infectivity, transovarial transmission, and trans stadial transmission are included in the model to simulate transmissio n of the Lyme disease spirochete between vector ticks and vertebrate h osts. Validity of LYMESIM was established by comparing simulated and o bserved populations of immature I. scapularis on white-footed mice, Pe romyscus leucopus, (Rafinesque), at 2 locations in Massachusetts. Vali dity also was indicated by comparisons of simulated and observed seaso nality of blacklegged ticks in New York, Massachusetts, Florida, and O klahoma-Arkansas. Further model validity was shown by correlation betw een simulated and observed numbers of immature ticks engorging on whit e-footed mice at 3 sites in Massachusetts. The model produced acceptab le values for initial population growth rate, generation time, and 20- yr population density when historical meteorological data for 16 locat ions in eastern North America were used. Realistic rates of infection in ticks were produced for locations in the northeastern and northcent ral United States. LYMESIM was used to study the effect of white-foote d mouse and white-tailed deer, Odocoileus virginianus (Zimmerman), den sities on tick density and infection rates. The model was also used to estimate tick density thresholds for maintenance of B. burgdorferi.