a b s t r a c t
Human demands on natural resources result in landscape changes that facilitate the emergence of disease.
Most emerging diseases are zoonotic, and some of these pathogens play a role in the decline of vulnerable
wildlife species. Baylisascaris procyonis, the common roundworm parasite of raccoons (Procyon
lotor), is a well recognized zoonotic infection that has many of the properties associated with a pathogen
capable of driving extinction. It is highly non-specific and frequently pathogenic with regard to paratenic
hosts, which contact eggs of B. procyonis at raccoon latrines. Eggs accumulate at latrines and remain viable
for many years. Transmission of B. procyonis is sensitive to changes in land-use, and fragmented habitats
increase contact rates between raccoons, potential paratenic hosts, and the parasite. Raccoons, and
subsequently B. procyonis, have been introduced to Europe and Japan, where naïve vertebrates may be
exposed to the parasite. Finally, domestic animals and exotic pets can carry patent infections with B.
procyonis, thus increasing environmental contamination beyond raccoon latrines, and expanding the area
of risk to potential paratenic hosts. This parasite can potentially contribute to extinctions of vulnerable
species, as exemplified by the case of the Allegheny woodrat (Neotoma magister), a species that has experienced
local declines and extinctions that are linked to B. procyonis. Conservation strategies for vulnerable
species should consider the transmission ecology of parasitic pathogens, like B. procyonis.