Consideration of an association between geographic distribution of caves and occurrence of rabies in foxes.

Establishing a causative relationship for the association between geographic distribution of caves and the occurrence of rabies in foxes in the United States will require the demonstration of a plausible biological mechanism and proof from carefully designed epidemiologic studies. Considerable data implying biological plausibility exists in the form of rabies as an enzootic disease in bats, bat predation by ground animals, bat migratory patterns, and several possible virus transmission routes to the fox. Further data showing development of rabies in the fox following appropriate bat contact are needed. Evidence leading to the acceptability of a causal relationship should distinguish between spurious, causal, and indirect hypotheses. An alternative hypothesis is whether cave areas are superior fox habitats and harbor far greater populations of foxes than do noncave areas.