Infection dynamics of Ichthyophthirius multifiliis

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Abstract
The dynamics of infection of the fish host Poecilia latipinna by free-swimming tomites of the ciliate Ichthyophthirius multifiliis and the age-dependent survival of these infective stages are examined experimentally. Simple deterministic models are developed to aid the analysis of experimental results. Under defined laboratory conditions it is found that virtually all recently emerged infective stages successfully locate a host and that there appear to be no density-dependent constraints on parasite establishment on naive hosts. The overall reproductive success of the parasite is therefore shown to be determined by the proportion of infective stages encountering a host that are able to develop to form adult parasites. Variability between hosts in proportional establishment is postulated as the generating mechanism of the high observed heterogeneity in parasite burden/host. A model is described which predicts a simple relationship between mean parasite burden and variance in burden/host.