Epizootics of diphyllobothriidean cestodes appear to be simple, but deceptive similarity conceals the myriad ways in which these events are shaped by complex abiotic and biotic interactions. In Dog Bone Lake, Alaska, an epizootic of Schistocephalus pungitii infecting the ninespine stickleback (Pungitius pungitius) was short-lived. Its duration, with a peak that lasted only 1 yr, was shorter than for previously documented epizootics in Schistocephalus solidus. The ability of the ninespine stickleback to sustain infections, which appears to be related to species-specific characteristics of the host, may have played an important role in shaping the epizootic. Moreover, the epizootic of S. pungitii was not coincident with those observed for S. solidus in earlier studies within this region, supporting the hypothesis that processes involved in epizootics largely reflect local (lake-level) influences on population dynamics of the parasite. The outbreak occurred at a time when the host population was not relatively dense, which is inconsistent with epidemiological theory and may be a consequence of the parasite′s indirect life cycle. The variability of the unregulated and unstable epizootic events of diphyllobothriidean cestodes presents a challenge to understand the ecological and evolutionary factors influencing the prevalence of infections in host populations.

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