Lyme Disease Using Parallel Discrete Event Simulation

Lyme Disease affects many people in the northeastern United States. One of the most important mechanisms that sustains the epidemic is the interaction between white-footed mice (Peromyscus leucopus) and deer ticks (Ixodes scapularis). When mice move around in their territory they carry diseased ticks to new locations. Our system simulates the different developmental stages of the tick through its active spring/summer period. The system uses the optimistic protocol for Parallel Discrete Event Simulation. In this paper, we present the model of the spread of the disease. We describe how we parallelize the problem, and we sketch a new global virtual time algorithm used in our system. We present performance benefits resulting from a parallel platform. 1 BIOLOGICAL OVERVIEW Lyme Disease is caused by a spirochete (Borrelia burgdorferi) which is most commonly present in ticks (Barbour and Fish 1993, Miller et all 1990). When an infected tick feeds on an animal or human, the spirochete may be transferred into the host's blood stream, causing an infection. Since the ticks are practically immobile, the spread of the disease is driven by their mobile hosts, such as mice and deer. An infected tick might infect a mouse, which in turn may infect an uninfected tick at a new location. The life cycle of ticks encompasses several stages over a period of two years. The eggs hatch in the summer and become larvae. If a larva is successful in feeding on a host, it molts into a nymph. The nymphs that survive the winter, and that are able to find a blood meal during the spring, molt into adults. Adult female ticks deposit eggs. Ticks are assumed to hatch uninfected. The ticks in their larval and nymphal stages prefer to feed on mice whereas the adults prefer deer. Ticks that are unable to find a Thomas Caraco Department of Biological Sciences State University of New York at Albany Albany, NY 12222