Ecology and transmission dynamics of Baylisascaris procyonis

Laura Kristen Page, Purdue University

Abstract

I studied ecological factors affecting transmission dynamics of Baylisascaris procyonis, the common large roundworm of raccoons ( Procyon lotor) to intermediate hosts. Infective eggs of B. procyonis are present at raccoon latrines, and these sites may be important in the transmission of this parasite to small vertebrates in forested areas. I found that raccoon latrines exhibited characteristics generally associated with treefall gaps, and that B. procyonis eggs were present at 14% of the raccoon latrines sampled. Seventeen mammal and 19 bird species visited latrines during October–November 1994–1997. Small granivorous mammals, including white-footed mice (Peromyscus leucopus), eastern chipmunks (Tamias striatus), and tree squirrels (Sciurus carolinensis , S. niger, Tamiasciurus hudsonicus) were the most common visitors to latrine sites. Active foraging among raccoon feces was documented for five vertebrate species and accounted for 10% of all recorded events. Type of seed present in experimentally manipulated feces only affected visitation rates of white-footed mice, which increased when corn was present. This suggests that transmission of B. procyonis to white-footed mice is increased in agricultural areas. Among white-footed mice, prevalence of larval B. procyonis, intensity of infection, and larval load were significantly higher in a highly fragmented agricultural landscape than in a predominantly forested landscape. Within the agricultural landscape, regression models successfully predicted probability of infection, intensity of infection, and larval loads as increasing functions of forest patch area and isolation. The role of latrines in transmission of B. procyonis to white-footed mice was studied in ten 500 m2 enclosures. Levels of ambient food availability and length of exposure were varied among trials to develop predictive models of risk of infection and of mortality due to central nervous system (CNS) disease. Fifty percent of experimental mice acquired B. procyonis infections, and 43 percent of infected mice developed CNS disease. Regression models successfully predicted probability of infection as a function of trial length and frequency of latrine visitation, and probability of mortality due to CNS disease as a function of food availability and frequency of visitation. I conclude that transmission of B. procyonis occurs at raccoon latrines where many species of vertebrates visit and forage among feces.

Degree

Ph.D.

Advisors

Kazacos, Purdue University.

Subject Area

Ecology|Forestry

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