RÉSUMÉ
Baylisascaris procyonis , the raccoon ( Procyon lotor ) ascarid, is a common roundworm parasite of raccoons that is also a well-recognized zoonotic pathogen, and a cause for conservation concern. The transmission dynamics of B. procyonis differ with host population attributes, season, and landscape. We examined how the parasite's population attributes change with season, parasite population structure, and host demographics. We examined 1,050 raccoon gastrointestinal tracts collected from 1996 to 2012. Of the 1,050 raccoons necropsied, 382 (36%) were infected with at least one B. procyonis (x¯=15.8 [95% confidence interval=13.39-18.26]; median=7; range 1-199 worms/host), and populations were overdispersed. There was a seasonal change in prevalence with a peak in October/November. Worm burdens decreased approximately 28% per month from January to June and increased approximately 31% per month from June to December. The sex structure of B. procyonis populations was female-biased (56% female). Host demographics did not impact parasite population attributes. This study provides evidence that B. procyonis populations exhibit a yearly cycle of loss and recruitment that may impact the transmission dynamics of the parasite.