Strongylus vulgaris

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Geographic Range

This parasite can be found worldwide; its dispersal is dependent on where its hosts (equines) are found. (Corwin and Nahm, 1997)

Habitat

Strongylus vulgaris is found primarily in grasslands and pastures. They are essentially located where equine populations are concentrated. (Corwin and Nahm, 1997)

Physical Description

These worms are cylindrical, dark red in color, with male adults approximately 2.5 to 4 cm in length, while females range from 4 to 6 cm. There are five larval stages before adulthood is reached. The buccal capsule, which adults use to feed, is relatively large and heavily sclerotized, with two lobed teeth. The anterior region is dorsally curved, giving the appearance characteristic of hookworms.

The cuticle has three or more main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals.

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; Corwin and Nahm, 1997; Roberts and Janovy, 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    2.5 to 6 cm
    0.98 to 2.36 in

Development

The life cycle of S. vulgaris involves five juvenile stages and its equine host. Eggs are found in its host feces, where they hatch and the juveniles feed on the feces through the third larval stage. At this point, they crawl onto vegetation the equines feed on, where they are ingested by the host. Once in the small intestine, the third-stage juvenile penetrates through the intestinal wall and molts into its fourth larval stage. The larvae penetrate the surrounding arteries and make their way to the mesenteric arteries, where they develop into the fifth larval stage, immature adults. The immature adults make their way back to the intestines, where they encapsulate themselves and develop into adults. The adults hatch from the capsules and mate, producing eggs which are passed out in the feces. (Johnstone, 1998)

Reproduction

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. (Barnes, 1987; Roberts and Janovy, 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning

Behavior

This strongyle doesn't have any distinguished social characteristics; most of the interaction occurs in its host's intestine during mating. (Johnstone, 1998)

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; Roberts and Janovy, 2000)

Food Habits

Through the first three larval stages of development S. vulgaris feeds upon the feces of its parent's host. The later larval stages are found in the circulatory system of equines, feeding on blood and tissue as it makes its way through different areas of the body. The adults are primarily found in the intestine and associated organs, where their feeding can cause major damage to the gastrointestinal organs. (Corwin and Nahm, 1997)

  • Animal Foods
  • blood
  • body fluids
  • Other Foods
  • dung
  • microbes

Predation

These parasites are probably not preyed on directly, but are likely ingested by various animals. Larval mortality is high as most of the parasites do not reach appropriate hosts.

Ecosystem Roles

Strongylus vulgaris is parasitic on horses. (Johnstone, 1998)

Species Used as Host

Economic Importance for Humans: Negative

Strongylus vulgaris has at times been a very common parasite in horses; it was estimated that it was present in 90% to 100% of horses in the U.S. The inflammation caused by the strongyle travelling throughout the arteries and intestines can cause blood clots to form. The clots can block oxygen passage to the intestines, causing parts of them to die. Ultimately, besides causing abdominal pain (colic) in equines, the complications from S. vulgaris infestation can lead to death.

S. vulgaris is no longer considered as much of a threat to horses, because it can be controlled by drugs such as benzimidazoles, ivermectin, and moxidectin, which kill both larvae and adult stages of the worm. (Herd, 1990; Roberts and Janovy, 2000)

Contributors

Renee Sherman Mulcrone (editor).

Nathan Lenneman (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

Glossary

Australian

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

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Ethiopian

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

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Nearctic

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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Neotropical

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

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Palearctic

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

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agricultural

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.

carnivore

an animal that mainly eats meat

causes or carries domestic animal disease

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

chaparral

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.

chemical

uses smells or other chemicals to communicate

coprophage

an animal that mainly eats the dung of other animals

cosmopolitan

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.

ectothermic

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

fertilization

union of egg and spermatozoan

forest

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

heterothermic

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

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

mountains

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

oriental

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

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oviparous

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

parasite

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

pheromones

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

rainforest

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.

sedentary

remains in the same area

sexual

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

suburban

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

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

taiga

Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.

temperate

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).

terrestrial

Living on the ground.

tropical

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.

savanna

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.

tundra

A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.

urban

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

References

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

Corwin, R., J. Nahm. 1997. [Published lecture notes on Strongylus vulgaris]. MO: University of Missouri College of Veterinary Medicine.

Herd, R. 1990. The changing world of worms: The rise of cyathostomes and the decline of Strongylus vulgaris. Comp. Cont. Ed. Pr. Vet., 12: 732-736.

Johnstone, C. 1998. Parasites and Parasitic Diseases of Domestic Animals. Philadelphia, Pennsylvania: University of Pennsylvania School of Veterinary Medicine. Accessed September 29, 2004 at http://cal.vet.upenn.edu/merial/Strongls/strong_8d.htm.

Roberts, L., J. Janovy. 2000. Foundations in Parasitology, 6th ed.. Boston: McGraw-Hill Companies, Inc..