Trichinella pseudospiralis

Geographic Range

Trichinella pseudospiralis thrives in many areas around the world. First isolated from the skeletal muscles of a raccoon in Russia, its wide geographic range today is attributed to its main hosts, which are birds. The parasite has spread widely with the migration of birds. Trichinella pseudospiralis is limited by temperature, and does not survive in extreme climates. (Smyth, 1962)


Trichinella pseudospiralis lives on terrestrial animals. The primary hosts for these worms are birds, and they are commonly seen on captive American kestrels. They have a wide distribution that is limited by temperature. This parasite is seen in domestic environments as well as temperate, torrid, and frigid zones. (Smyth, 1962)

Physical Description

Both adult males and females are of nearly uniform diameter and measure around 2.46 mm in length. Females are larger than males. They gradually increase in thickness posteriorly. The head of the worm is tapered and round. Adults possess a mouth stylet which is used to cut host tissues and vessels. Trichinella species have larvae that are made up of two definite layers separated by membrane. The inner layer has a large amount of very fine fibrils, arranged parallel to the circumference of the larvae. There is also a thin external membrane present. (Barnes, 1987; Gould, 1970; Lee, 1965)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Average length
    2.46 mm
    0.10 in


The fertilized egg develops into a coeloblastula, which is followed by gastrulation, and by the formation of embryos. These embryos fill the uterus of the adult female worm by the 5th or 6th day after copulation. As many as 1500 larvae can be deposited by one worm. Once the mother has deposited the larvae, they penetrate the mucosa and are carried to the voluntary muscles, especially those of the diaphragm, jaws, tongue, larynx and eye. After their migration, other species of Trichinella, such as T. spiralis, form cysts and remains in the host muscle. Trichinella pseudospiralis is different because it does not induce capsule formation in host muscles. The larva is passed to other hosts by an animal eating the flesh of another infected animal or its feces. (Gould, 1970; Smyth, 1962)


Trichinella species are unique in that all stages of their life cycle occur with in a single host. Copulation occurs around 30 to 40 hours after the host has been infected with the parasite. The ovum is fertilized within the female's body by the male sperm. The fertilized egg develops into a coeloblastula, which is followed by gastrulation, and by the formation of embryos. These embryos fill the uterus of the adult female worm by the 5th or 6th day after copulation. As many as 1500 larvae can be deposited by one worm. (Gould, 1970; Smyth, 1962)

  • Range number of offspring
    1500 (high)
  • Parental Investment
  • pre-fertilization
    • provisioning


These worms are capable of active coiling and uncoiling. They are able to undergo a considerable degree of contraction and expansion. The coiling action is most pronounced in the anterior portion of the worm. (Gould, 1970)

Communication and Perception

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

Food Habits

Trichinella pseudospiralis has the same intermediate and definitive host. It spends its entire life in that one host. The juvenile parasite feeds inside the muscles of its host. Using its stylets it cuts open the host cells and feeds on the intracellular material that flows out. The Trichinella repeatedly protrude and retract the stylet in order to get through the host tissue. This process releases cell contents and other fluids that, together with the products of histolysis, are ingested by active pumping of the pharynx. The adults living in the intestine have a stylet as well. However, the adult Trichinella feed on the intestinal mucosa of the host rather than on its intestinal contents. (Gould, 1970)

  • Animal Foods
  • body fluids


These parasites are probably not preyed on directly. However, larval mortality is high since most larvae do not reach the proper host species.

Ecosystem Roles

Trichinella pseudospiralis lives on terrestrial animals. The primary hosts for these worms are birds. (Smyth, 1962)

Species Used as Host

Economic Importance for Humans: Negative

Since the main hosts of Trichinella pseudospiralis are birds, their parasitism has an effect on humans. Endangered species, as well as birds that are bred in captivity are threatened. Natural infections with the nematode are known to cause severe debilitation and death in Cooper's hawks. Trichinella pseudospiralis also causes behavioral changes and decreases the reproductive success of captive American kestrels. Infected pairs of the birds produce significantly fewer offspring than their uninfected counterparts, which can cause a great amount of economic loss for breeders.

Not all of the effects of Trichinella pseudospiralis are seen in both sexes, during all periods of the host's life cycle, or during all times of the day. Both sexes were observed to fly much less and they scratched more frequently. Infected females exhibited an increase in the frequency of aggressive displays in the late morning, which suggests that they may be less receptive to mating than uninfected females. Males seemed to feel the pains of hunger stress more than the infected females (Saumier et. al 1991). (Saumier, et al., 1991)

Conservation Status

Other Comments

Until recently, all species in the genus Trichinella were considered to be one species: Trichinella spiralis. Now, it is understood that there are four species that belong to this genus. It was because of their extreme similarity morphologically that they were indistinguishable. It was just recently discovered that a collagenous capsule or cyst is not present around the nurse cell of Trichinella pseudospiralis and therefore it is a different species. Because of the recency of this discovery the species Trichinella pseudospiralis is extremely under-researched, and there is not much information available on the subject. (Saumier, et al., 1991)


Renee Sherman Mulcrone (editor).

Henna Tirmizi (author), University of Michigan-Ann Arbor, Teresa Friedrich (editor), University of Michigan-Ann Arbor.



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.

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.

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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


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.


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.


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.


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


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

Gould, S. 1970. Trichinosis in Man and Animals. Springfield, Illinois: Charles C. Thomas Publisher.

Lapage, G. 1968. Veterinary Parasitology, Second Edition. Edinburgh and London: Oliver & Boyd.

Lee, D. 1965. The Physiology of Nematodes. San Fransisco: W.H. Freeman and Company.

Saumier, M., M. Rau, D. Bird. 1991. Behavioral changes in breeding American kestrels infected with Trichinella pseudospiralis. Bird-Parasite Interactions, Ecology, Evolution, and Behavior: 290-313.

Smyth, J. 1962. Introduction to Animal Parasitology. London: Cambridge University Press.