Baylisascaris procyonis

Geographic Range

Baylisascaris procyonis is a parasitic roundworm that lives inside a raccoon's (Procyon lotor) digestive track and is native to North America, Europe, and parts of Asia. Other species to carry this parasite are white-footed mice (Peromyscus leucopus), cats (Felis catus), dogs (Canis lupus familiaris), birds, chipmunks (Sciuridae), and squirrels (Family Sciuridae). One particular animal whose numbers have greatly increased on being infected with this roundworm, is the Allegheny woodrat (Neotoma magister). The roundworm can also parasitize humans (Homo sapiens). They often ingest this parasite from drinking contaminated water or coming in contact with contaminated soil.

In North America this roundworm is most commonly found in the midwestern and northeastern regions. In the United States it is less common to come across this roundworm. The exception to this rule is the state of Georgia, there has been a steady rise in the instance of this roundworm being found. The raccoons that were studied to have this roundworm in the southeastern areas were found to live in mountainous areas. Since 1977, Japan began importing raccoons as pets. The raccoons that were released or escaped into the wild, introduced the roundworm into central Honshu and Hokkaido. (Snyder and Fitzgerald, 1985)


The common habitats where raccoons are found that have this roundworm are in forests, mountains, urban areas, and in the suburbs. The roundworm is usually not harmful to the raccoon and live inside their intestinal track, mainly the small intestine and it's eggs are shed in it's feces. The raccoons usually have one spot at which they will defecate, called latrines. There are many smaller animals that will forage through raccoon feces in search of seeds and instead ingest roundworm eggs.

If the eggs are embryonated, they will hatch inside their new host's gut and become larvae. The larvae will migrate out of the gut and through the animal, towards the central nervous system. From there, the roundworm larvae will cause extensive damage that most often results in the death of the host.

The roundworm larvae are protected by the deceased host's body and will reach sexual maturity there. If the deceased host's body is scavenged by a raccoon then the cycle continues. (Logiudice, 2001)

Physical Description

The eggs of the roundworm are spherical in shape with radial symmetry and range from 63 to 88 micrometers by 50-70 micrometers and are dark brown in color. The adult roundworm is tan in color, has bilateral symmetry, tubular shaped, and varies in size depending on the sex and size of its host. The adult male roundworm can be as small as 57 millimeters long but can obtain lengths up to 12 centimeters. The female roundworm typically is larger, ranging from 87 millimeters to 24 centimeters. Like all roundworms, males have a hook on their tail end, which holds copulatory spicules. (Gavin, et al., 2005; Overstreet, 1970)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    24 (high) cm
    9.45 (high) in


The infection of Baylisascaris procyonis most often begins with an infected raccoon (Procyon lotor). It contains an adult egg-laying roundworm in its small intestine. The eggs will be released in the raccoon's feces. The amount of eggs per defecation can average around 20,000-26,000 in number. This is where the egg will grow and develop into an embryonated egg. Another animal can become infected with this roundworm by ingesting the eggs or by ingesting an already infected animal host. At the time of ingestion the egg is already embryonated and will remain in the host's intestine until it hatches. This is considered the first stage of development. The second stage is when the larva hatches and begins to migrate through its host body. The larva will then make its way through the intestinal wall to bloodstream of its host and may make it to their liver and/or lungs. The likelihood of the larva making it to the host's central nervous system or eyes is about 5% or more of the number ingested. The third stage is marked by the growth and development of the larva in these tissues. The size the larva can reach is 1300 to 1900 micrometers in length, and 50 to 80 micrometers in width. This third stage growth occurs in a timespan of 2 to 4 weeks. The larva will then make its way back to the host's intestinal track and reach maturity there. (Bauer, 2013; Gavin, et al., 2005)


Specific information on the mating of Baylisascaris procyonis was unable to be found but it's suspected that this species mates similar to most nematodes.

Typically, the male nematode uses a ciliated sensory neuron that is found in his head and tail to locate a female. The nematode will then wrap his tail around the female in order to find her vulva opening. When successful, he will then transfer his sperm directly into her vulva opening via his copulatory spicules. This fertilization is internal. (Yager and Emmett, 2012)

An adult female Baylisascaris procyonis can start producing eggs 50-76 days after hatching in its host. The adult female roundworm can generate around 115,000-179,000 eggs per day.

In colder regions, during the winter months, there have been noted declines in infection and production of eggs. This is speculated to be possible if the host cures itself of the infection or due to the host hibernating. Egg production and infection steadily increases in the spring months and the heaviest amount of infections occurring in the fall. (Bauer, 2013; Kazacos, 2001; Page, 2013)

  • Breeding interval
  • Breeding season
    Year round, but peak seasons being in Spring and Fall
  • Range number of offspring
    115,000 to 179,000
  • Range time to independence
    immediate (low) days
  • Range age at sexual or reproductive maturity (female)
    50 to 76 days

No parental involvement for Baylisascaris procyonis was found.

  • Parental Investment
  • no parental involvement


No documentation on the lifespan of Baylisascaris procyonis was found. However, if the eggs are in soil with adequate moisture they can remain viable for years. An exact number of years has not been documented. (Gavin, et al., 2005)


This nematode's stage of life will affect its behavior. These behaviors include mating, egg production, and actively migrating through the host's body to prepare for maturity and reproduction. Mating consists of the male roundworm finding a female and depositing its sperm internally. Communication of Baylisascaris procyonis was not found but is thought to be similar to that of nematodes. Nematodes will communication by using pheromones, chemicals, and seismic vibrations. The chemicals utilized by these roundworms were not specified. (Bauer, 2013; Gavin, et al., 2005; Torr, et al., 2004)

Home Range

Due to the nature of its parasitic lifestyle, Baylisascaris procyonis does not maintain a home range. (Kazacos, et al., 2013)

Communication and Perception

Specific information on the communication and perception of Baylisascaris procyonis was not found but information on its phylum, Nematoda, was available.

The nematode exhibits cephalization, with a nerve bundle at its anterior end and nerve cords that run the length of its body. The nematode also has cuticular sense organs that detect chemicals, mechanical stimuli, and temperature. This roundworm possesses simple eyes called ocelli. Ocelli contain one lens and they run the length of the nematode's body, allowing the individual to sense light. (Jones, 2002)

Food Habits

As a parasite, this roundworm obtains all nutrients from its host. The animals listed in the habitat section are just a few of the potential hosts for this roundworm. During the roundworm's time in the intestinal tract, it will consume nutrients the host has eaten. It will feed on various tissues and organs of its host on its way through the body to the central nervous system. (Gavin, et al., 2005; Logiudice, 2001)

  • Animal Foods
  • birds
  • mammals
  • body fluids


The eggs of Baylisascaris procyonis can survive for years outside of the host if the right conditions are met (moisture and temperature). This allows for the longevity of the eggs and increased chances for infecting a new host. These roundworms can also invade the host's central nervous system causing death. The life cycle is perpetuated when the host body is scavenged by a new raccoon.

These roundworms have been able to survive treatments of anthelmintics and corticosteroids in parasitized humans. Killing these parasite has proven to be quite a challenge once the parasites have spread through the host's body.

A specific predator of Baylisascaris procyonis was not found but predators of nematodes and roundworms were. Earthworms (Lumbricus terrestris) and dung beetles (Scarabaeidae) are known to feed on the eggs and larvae. There are also varieties of fungi that will trap and consume the larvae. (Gavin, et al., 2005; Johnson, et al., 2010)

  • Known Predators
    • Dung beetles (Scarabaeidae)
    • Earthworms (Lumbricus terrestris)
    • Fungi

Ecosystem Roles

Baylisascaris procyonis impacts the health and livelihood of 70 or more species of small forest mammals and birds in a negative way. Baylisascaris procyonis is also a zoonotic parasite that has also caused ocular and central nervous system disease once infected and most often ends in death. (Page, 1998)

Species Used as Host

Economic Importance for Humans: Positive

There are no known positive economic impacts of Baylisascaris procyonis on humans.

Economic Importance for Humans: Negative

Though it is rare, humans have been parasitized by Baylisascaris procyonis. As of 2005, there were 13 confirmed cases. Of those 13, 5 died and the other 8 where left severely impaired. The tests to diagnose and to treat this type of infection are costly and have been mostly unsuccessful. (Gavin, et al., 2005; Wise, et al., 2005)

Conservation Status

As a parasite, no threats to this roundworm are known. No conservation measures have been implemented for this species.

Other Comments

There is fear of Baylisascaris procyonis being used for bioterrorism. Because Baylisascaris procyonis produces a large number of eggs and these eggs can stay in an active parasitizing form for long periods of time (no time frame specified), and the fact that they are easily obtainable make it a possible bio-terrorist agent. The introduction of this parasite's eggs into a water system could create an outbreak. Also, this parasite is most often fatal to humans and there isn't an effective treatment or vaccine in existence. (Sorvillo, et al., 2002)


Melissa Kesterson (author), Radford University - Fall 2015, Cari Mcgregor (editor), Radford University, Zeb Pike (editor), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Jacob Vaught (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).


uses smells or other chemicals to communicate


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


found in the oriental region of the world. In other words, India and southeast Asia.

World Map


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


living in cities and large towns, landscapes dominated by human structures and activity.


uses sight to communicate


Bauer, C. 2013. Baylisascariosis—Infections of animals and humans with ‘unusual’ roundworms. Veterinary Parasitology, 193/4: 404-412.

Gavin, P., K. Kazacos, S. Shullman. 2005. Baylisascaris. American Society for Microbiology, 18/4: 703-718.

Johnson, P., A. Dodson, K. Lafferty, D. Marcogliese, J. Memmott, S. Orlofske, R. Poulin, D. Thieltges. 2010. When parasites become prey: Ecological and epidemiological significance of eating parasites. Trends in Ecology & Evolution, 25/6: 362-371.

Jones, J. 2002. Nematode sense organs. Pp. 693-722 in Lee, ed. Biology of Nematodes. London, UK and New York, USA: Taylor & Francis.

Kazacos, K. 2001. Baylisascaris procyonis and related species. Pp. 301-341 in W Samuel, M Pybus, A Kocan, eds. Parasitic Diseases of Wild Mammals. Ames, Iowa: Iowa State Univeristy Press.

Kazacos, K., L. Page, R. Swihart. 2013. Changes in transmission of Baylisascaris procyonis to intermediate hosts as a function of spatial scale. Oikos, 93/2: 213-220.

Logiudice, K. 2001. Latrine foraging strategies of two small mammals: Implications for the transmission of Baylisascaris procyonis. The American Midland Naturalist, 146/2: 369-388.

Overstreet, R. 1970. Baylisascaris procyonis (Stefanski and Zarnowski, 1951) from the kinkajou, Potos flavus, in Colombia. Proceedings of the Helminthological Society, 37/2: 192-195.

Page, L. 1998. Ecology and Transmission Dynamics of Baylisascaris procyonis (Ph.D. Dissertation). West Lafayette, IN: Purdue University.

Page, L. 2013. Parasites and the conservation of small populations: The case of Baylisascaris procyonis. International Journal for Parasitology: Parasites and Wildlife, 2: 203-210.

Snyder, D., P. Fitzgerald. 1985. The Relationship of Baylisascaris Procyonis to Illinois raccoons (Procyon lotor). The Journal of Parasitology, 71/5: 596-598.

Sorvillo, F., L. Ash, O. Berlin, J. Yatabe, C. Degiorgio, S. Morse. 2002. Baylisascaris procyonis: an emerging helminthic zoonosis.(Synopsis). Emerging Infectious Diseases, 8/4: 355-360.

Torr, P., S. Heritage, M. Wilson. 2004. Vibrations as a novel signal for host location by parasitic nematodes. International Journal for Parasitology, 34/9: 997-999.

Wise, M., F. Sorvillo, S. Shafir, L. Ash, O. Berlin. 2005. Severe and fatal central nervous system disease in humans caused by Baylisascaris procyonis, the common roundworm of raccoons: A review of current literature. Microbes and Infection, 7/2: 317-323.

Yager, M., M. Emmett. 2012. How worms' sex behavior can have a major impact on understanding human disease. Proceedings (Baylor University Medical Center), 25/4: 395-396.