Changes in transmission of Baylisascaris procyonis to intermediate hosts as a function of spatial scale

Physical changes in landscapes alter the abundance and distribution of spec ies. Higher-order effects can occur when changes in ecological processes re sult in altered interspecific interactions and subsequent changes in a spec ies' abundance or persistence. Baylisascaris procyonis, a roundworm parasit e of raccoons (Procyon lotor), is pathogenic to numerous small vertebrates that serve as intermediate hosts, including white-footed mice (Peromyscus l eucopus). Raccoons have responded positively to agriculturally induced chan ges in landscapes, with potential consequences for intermediate hosts of B. procyonis. We examined white-footed mice from a homogeneous, predominantly forested landscape in south-central Indiana and a heterogeneous, predomina ntly agricultural landscape in northwestern Indiana for presence of larval B. procyonis. We compared prevalence of infection, intensity of infection, and average number of larvae per mouse between the landscapes, and among fo rest patches within the highly fragmented agricultural landscape. Prevalenc e, intensify of infection, and average number of larvae were significantly higher in the highly fragmented landscape. Within the agricultural landscap e, regression models predicted probability of infection, intensity of infec tion, and average number of larvae per mouse per patch as functions of fore st patch area and isolation. We conclude that positive responses of raccoon s to agriculturally induced fragmentation of forests have resulted in incre ased encounter rates between white-footed mice and infective stages of B. p rocyonis between and within landscapes, resulting in increased transmission of the parasite to intermediate hosts.