Planning for rabies control in Ontario

Ten geographic cells of rabies cases were identified within southern Ontario. Some had regular 3-year peaks, whereas others had weak cycles with mean periods of up to 9 years. Incidence of rabies was related to soil types (highest on sandy and clay loams), land use (abundant where hay and pasture were dominant), and drainage (poor drainage supported only low levels of rabies). A spatial stochastic simulation model is being used to evaluate risks and tactics associated with reduction of rabies by use of vaccine baits. The model indicated that persistence of rabies is unlikely in areas with less than 4,000 km2 of contiguous fox habitat. In sensitivity tests the model was most affected by the values of four input parameters: rate of contact among foxes, incubation period of rabies, fox density, and a density-dependent feedback that reduces fox recruitment when density approaches or exceeds a predetermined "carrying capacity." In a majority of model experiments, a single vaccination of 60% of a fox population eradicated rabies, but only if vaccination took place just after a rabies outbreak, when the number of both foxes and rabid animals was reduced. Rabies control will probably be applied to individual cells or clusters of cells rather than to the entire 98,000 km2 enzootic zone, at least at first. If rabies is eradicated the fox populations may increase, but modestly. Skunks were more important than foxes as vectors of rabies in urban Ontario. Since there is no effective oral rabies vaccine for skunks, skunks were trapped alive and vaccinated by injection.(ABSTRACT TRUNCATED AT 250 WORDS)