Baylisascaris Infection Rates in Mice Vary with Deforestation

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The authors of an article featured in The Journal of Parasitology explore parasitic roundworm Baylisascaris procyonis infection rates among animals living near developing land. They discovered the intensity and abundance varied widely depending on the areas' size and connection to other forested areas.

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The larger and more connected the wild areas to other forested sections, the less prominent the infection.

Journal of Parasitology – Any parasite that can spread from wild animals to people is a concern. Even when human infections are rare, as in the case of the parasitic roundworm Baylisascaris procyonis, scientists need to learn as much as they can about the parasite that transmits disease and the animals that host the parasite.

The authors of an article published in the current issue of the Journal of Parasitology studied B. procyonis. The researchers were particularly interested in determining whether animals living near land being developed showed a pattern of significant infection rates.

Usually found in raccoons, B. procyonis also infects small rodents when they eat undigested seeds, particularly corn, in raccoon scat. People can become infected if they accidentally ingest the roundworm’s eggs, which is most likely to occur when children, for example, put dirt in their mouths. After infection, the parasites migrate to the brain causing a severe or fatal encephalitis, and there is no good treatment for these migrating worms. B. procyonis has been discovered in the United States, Europe, and Japan and has reportedly infected animals in South America.

For the current study, the researchers trapped and tested 353 white-footed mice from 22 patches of forest in a largely agricultural area of northern Indiana. Both raccoons and mice frequent such areas in large numbers, potentially increasing the possibility of disease. The researchers developed models to predict whether the B. procyonis infection is common and intense in this environment.

They found infection from the parasite in all sampled areas, although the intensity and abundance of disease varied widely. The larger and more connected the wild areas to other forested sections, the less prominent the infection.

Raccoons in particular thrive in small patches of wild land with ready access to raidable grain fields. Therefore, in large forest patches with less frontage on croplands, mice find fewer raccoon latrines to use as a food source. Additionally, researchers concluded mice likely have smaller populations, which would account for the lower disease rates in the larger areas studied.

The study also showed that the size of a forested area, in particular the length of its perimeter, can affect how many animals are infected by B. procyonis, as well as the severity of their infection. Further research into the movements of raccoons within their home range and how this affects the parasite’s spread, as well as study of the landscapes the animals prefer, could produce more refined results.

Full text of the article “Baylisascaris procyonis infection in white-footed mice: predicting patterns of infection from landscape habitat attributes,” Journal of Parasitology, Vol. 99, No. 5, 2013, is now available.


About the Journal of Parasitology
The Journal of Parasitology is the official journal of the American Society of Parasitologists (ASP). It is a medium for the publication of original research, primarily on parasitic animals, and official business of the ASP. The journal is intended for all with interests in basic or applied aspects of parasitology as well as in systematics, medicine, molecular biology, immunology, physiology, ecology, biochemistry, and behavior. For more information, visit

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Kristen Vermeire
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