PARENT SESSION
Poster Session 17: Modelling
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

The influence of patch structure and host occupancy on whirling disease (Myxobolus cerebralis) dynamics in a stream reach scale model.

Kaeser, Adam^*,1, Reno, Paul¹, ¹ Hatfield Marine Science Center, Newport, OR

ABSTRACT- The success or failure of complex life cycle pathogens in novel environments is often tied to the distribution and abundance of vectors or alternate hosts. Recent outbreaks of the parasite Myxobolus cerebralis among wild trout in rivers of the Intermountain West has stimulated interest in the role played by the aquatic oligochaete Tubifex tubifex, the obligate second host in this system. Recent work has revealed both local and regional differences in the distribution and abundance of this worm that may account for variation in the trajectory of parasite invasions. T. tubifex worms are common among alpine rivers, but achieve unusually high abundance at organically enriched sites. It is unclear how such high density worm patches affect the dynamics of infection, and whether the remediation of such areas might ameliorate the impact of this parasite. We developed a stochastic, dynamic model of this 2-host system as a means to investigate such questions. Following the death and decay of an infected fish, parasite myxospores are released to fine sediment depositional habitats where they infect worm hosts. Triactinomyxon (TAM) spores are later shed from infected worms to the overlying stream water where they infect susceptible trout fry that randomly aggregate in the patches for a period of time following emergence. Using data from laboratory and field studies to estimate parameters, our model captures the dynamics of infection at the fine scale of a 1 m² depositional patch. At this scale, high worm density patches exhibit very different dynamics than low worm density patches in terms of TAM output and hence infection of fish occupying the patch. To explore the effect of worm distribution and abundance on infection dynamics at the stream reach scale, we varied the quantity and area of available patches, and the abundance of worms occupying these patches during model simulations.

Key words: parasite, model, river, patch