Foraging among feces:: Food availability affects parasitism of Peromyscus leucopus by Baylisascaris procyonis

Baylisascaris procyonis is a parasitic nematode of raccoons (Procyon lotor) capable of infecting many species of small vertebrates as intermediate hosts. In these hosts, migrating larvae often cause fatal or severe central nervous system (CNS) disease. Previous research suggested that intermediate hosts become infected with B. procyonis while visiting raccoon lat-tines. We tested effects of ambient availability of food and duration of exposure on dynamics of transmission of B. procyonis to white-footed mice (Peromyscus leucopus) in a factorial design within enclosures containing artificially constructed raccoon latrines. Fifty percent of experimental mice acquired B. procyonis infections and 43% of infected mice developed CNS disease. Visitation to latrines was marginally greater (P = 0.095) for mice subjected to low availability of ambient food. The mean number of larvae per mouse was greater (P = 0.001) in low food group after exposures of 14-28 days. Probability of infection varied predictably as a function of duration of exposure (P = 0.005), and probability of CNS disease varied predictably as a function of level of ambient food available (P = 0.023). We conclude that transmission of B. procyonis occurs at raccoon latrines and that increased visitation to latrines and duration of residence in close proximity to a latrine, both increase probability of mortality due to CNS disease, especially when individuals are stressed by reduced resources or poor habitat.