Document: ERI-3-55-10

Decaying reservoir competence and lyme disease ecology.

SCHAUBER, E.M.* ^1,2 and R.S.OSTFELD ²

University of Connecticut, Storrs, CT 06269 USA ¹
Institute of Ecosystem Studies, Millbrook, NY USA ²

Abstract:
Many vector-borne diseases require transmission from a reservoir host to the vector, which then infects other hosts (sometimes humans). Reservoir competence is the probability that a vector feeding on an infected host will become infected. A competent reservoir infects a large proportion of vectors that feed on it. Reservoir competence is also called "host infectivity", and is affected by the host immune response and the ability of the pathogen to escape that response. Reservoir competence varies among host species, but competence of an individual host also tends to decay over time since it was last infected, as its immune system suppresses the pathogen population or pathogens leave the bloodstream and invade other tissues. However, standard epidemiological models assume that reservoir competence is a species-specific constant. We explored the importance of reservoir competence decay for Lyme disease ecology using a simple epidemiological model with either one or two host species that differed only in the slope and intercept of competence decay curves. We compared the predictions of this model with predictions under the assumption that competence of each species was constant. We found that reservoir competence decay contributed positive feedback to this system: Hosts whose competence decayed rapidly were typically incompetent when infected vectors were scarce, reducing the infection prevalence of the vectors they fed. However, the same hosts had high competence when infected vectors were abundant, increasing the infection prevalence of the next vector generation. In a two-host system, competence decay caused the dilution effect of a less-competent reservoir to be considerably reduced at high densities of infected vectors. Similar results emerged from a more complex simulation incorporating seasonal dynamics of blacklegged ticks and their mammalian hosts. This mechanism may help explain the rapid rise in Lyme disease risk in areas of increasing tick populations, and highlights the potential impact of host community composition on the ecology and dynamics of this and other emerging diseases.

Keywords: Lyme disease, host community, epidemiology, reservoir competence, small mammals

This abstract is being presented at: 12:00 PM in session:
Oral Session #39: Theoretical Ecology.