Parascaris equorum

Geographic Range

Parascaris equorum are found worldwide, wherever horses and other equids are. (Von Brand, 1952)


When fully grown Parascaris equorum lives in the small intestines of the horse. (Monohan, et al., 1995)

Physical Description

Parascaris equorum is large, cylindrical, and has a cuticle with three layers made of collagen and other compounds that protect the worm from the acids in the digestive tracts of animals. The adult male ranges from 15-28 cm. The females are much larger and can grow up to 50 cm. Parascaris equorum has three very large lips. Each of these lips has a transverse groove or labial sinus on the lateral margins, which divide the lip into apical and basal regions. The eggs of Parascaris equorum are almost spherical and have a brownish color. The eggs contain a 1-celled zygote and are between 90-100 microns in size.

Nematodes have longitudinal muscles along the body wall. The muscles are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle. (Barnes, 1987; Brusca and Brusca, 2003; Gibbons, 1986; Roberts and Janovy, 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    15 to 50 mm
    0.59 to 1.97 in


Adult females are able to produce nearly 170,000 eggs daily. They are able to produce up to 60,000,000 eggs annually. The eggs are laid in the small intestine of the host and eventually exit the body in the feces. The life cycle of Parascaris equorum starts in the small intestine when the adult worms meet and mate. The eggs than travel through the intestines and end up in the feces. Prenatal infection is not known to occur. The egg then develops from the morula stage to the first juvenile stage to the second juvenile stage. If ingested by a horse, the egg travels to the small intestine where it hatches. The juvenile than penetrates the intestinal wall. The forth stage juvenile then travel into the alveoli and migrates back into the esophagus. After two more molts, the adults travel back to the small intestine and restart the cycle. (Drudge, et al., 1976; Hyman, 1951; Roberts and Janovy, 2000)


The life cycle of Parascaris equorum starts in the small intestine when the adult worms meet and mate. Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella. The eggs than travel through the intestines and end up in the feces. Adult females can produce nearly 170,000 eggs daily and up to 60,000,000 eggs annually. (Drudge, et al., 1976; Hyman, 1951; Roberts and Janovy, 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning


Parascaris equorum require 14-17 days for migration of the larvae through the liver and the lungs and 79-110 days to become gametogenically functional. (Hyman, 1951)


Parascaris equorum is a cosmopolitan parasite of the intestine of horses and other equids. Parascaris equorum require 14-17 days for migration of the larvae through the liver and the lungs and 79-110 days to become gametogenically functional. (Hyman, 1951; Roberts and Janovy, 2000)

Communication and Perception

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Barnes, 1987; Brusca and Brusca, 2003; Roberts and Janovy, 2000)

Food Habits

Parascaris equorum's main source of food is the liquid contents within the intestinal lumen. They eat by sucking up the liquid while moving through the intestines. It is probable that Parascaris equorum occasionally sucks the blood from the intestinal wall. (Roberts and Janovy, 2000)

  • Animal Foods
  • blood
  • body fluids


These parasites are probably not preyed on directly. Larval mortality is high as most of the parasites do not reach appropriate hosts.

Ecosystem Roles

This parasite infects horses and other equids. (Roberts and Janovy, 2000)

Species Used as Host

Economic Importance for Humans: Negative

Parascaris equorum affects the young horses most often. It can cause pneumonia, bronchial hemorrhage, colic, and intestinal disturbances. These symptoms can lead to sluggishness and morbidity. These roundworms may cause intestinal perforation or obstruction. The older horses commonly are immune to the infection. (Roberts and Janovy, 2000)

Conservation Status

Parascaris equorum is not in danger of extinction.

  • IUCN Red List [Link]
    Not Evaluated


Renee Sherman Mulcrone (editor).

Zachary Cooper (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.



lives on Antarctica, the southernmost continent which sits astride the southern pole.


Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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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.

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living in the southern part of the New World. In other words, Central and South America.

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

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living in landscapes dominated by human agriculture.

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 or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.


uses smells or other chemicals to communicate


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


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


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


having the capacity to move from one place to another.


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


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

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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


chemicals released into air or water that are detected by and responded to by other animals of the same species


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scrub forest

scrub forests develop in areas that experience dry seasons.


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


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


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


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


Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Drudge, , Lyons, Tolliver. 1976. Studies of the development and chemotherapy of larvae of Parascaris equorum in experimentally and naturally infected foals. Journal of Parasitology, 62(3): 453-459.

Gibbons, L. 1986. SEM Guide to Morphology of Nematode Parasites of Vertebrates. England: C.A.B. International.

Hyman, L. 1951. The Invertebrates: Volume 3. New York: McGraw & Hill, Inc..

Monohan, , Chapman, Taylor, French, Klein. 1995. Does titration of moxidectin oral gel against migrating Strongylus vulgaris and Parascaris equorum larvae in pony foals. Veterinary Parasitoogy, 60: 103-110.

Roberts, L., J. Janovy. 2000. Foundations of Parasitology: 6th Edition. Boston: McGraw & Hill, Inc..

Von Brand, T. 1952. Chemical Physiology of Endoparasitic Animals. New York: Academic Press Inc..