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Open Access Publications from the University of California

The epidemiology of a case of raccoon roundworm infection


The epidemiologic investigation of a recent case of cerebrospinal nematodiasis caused by the common raccoon intestinal roundworm (Baylisascaris procyonis) in an 11-month old child from Monterey County, California revealed a remarkable series of circumstances which led to the child’s infection. Human infection results from the inadvertent ingestion of eggs which are passed in large numbers (millions of eggs/day) in the feces of infected raccoons. Groups of raccoons typically defecate in common areas called latrines where the environmentally resistant B. procyonis eggs accumulate. Once infective-stage eggs are ingested, the immature larvae hatch and begin to migrate extensively and aggressively in tissues, frequently invading the spinal cord and brain. The one acre property where the child lived had extensive evidence of raccoon activity including 21 latrine sites. Fecal samples collected from the latrines and soil samples on the property were examined using concentration/flotation methods. All samples contained numerous embryonated B. procyonis eggs in both immature and fully infective larva stages. Unprecedented numbers of raccoons were observed living in the area and surrounding community. Further examination of the raccoon feces revealed that the raccoons using the latrines were eating corn and animal offal-based pet food provided by some residents in the area. Necropsies performed on 11 raccoons trapped on the property in connection with this investigation revealed that all (100%) were infected with B. procyonis. The patient’s behavioral history, large number of latrine sites, and the wide dispersal of raccoon feces observed on site indicated that the likelihood of exposure to infective B. procyonis eggs was extraordinarily high.

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