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Echinococcus granulosus

By Ann Walker

Geographic Range

This species has a worldwide distribution, found in both domestic and wild settings. Humans are infected especially in countries with extensive pastoral activities. The highest frequencies of E. granulosus are found in Eurasia, Africa, Australia, and South America. (Arambulo, 1997; Eckert, et al., 2000; Lightowlers, et al., 2000)

Habitat

Adult E. granulosus are found in the intestines of canines such as dogs, wolves or dingos. It can also be found in lions. Echinococcus granulosus larvae are found primarily in the lungs and liver, but may be found in any organ of the intermediate host. These hosts include sheep, moose, wallabies, camels, warthogs, and reindeer. Humans are most often infected with hydatid cysts in sheep-raising communitees. Accidental ingestion of E. granulosus eggs results from humans touching dogs that come in contact with livestock. (Roberts and Janovy, 2000)

Physical Description

The mature adult measures 3 to 9 mm long and consists of only 3 proglottids (the immature, mature and gravid), a scolex with four suckers, and a double crown of 28 to 50 hooks on the rostellum, at the tip of the scolex. Echinococcus granulosus may be found as a hydatid cyst in any organ of an intermediate host. The size of a cyst ranges from 4.1 to 7.2 cm and takes about 5 months to develop. Eggs of E. granulosus are indistinguishable from other taeniid eggs, typically 32-36 by 25-30 micrometers. (Kearn, 1998; Wardle, et al., 1974)

  • Range length
    3 to 9 mm
    0.12 to 0.35 in

Development

The gravid proglottid detaches from the adult and ruptures, releasing eggs into the feces of the definitive host. The intermediate host ingests eggs in contaminated food or water. The egg hatches to an oncosphere which develops into a unilocular hyatid cyst. Daughter cysts bud from the inner walls of the cyst via asexual reproduction, giving rise to numerous juveniles called protoscolices. Canids eat the intermediate host and hence acquire the protoscolices which develop to adults. (Ohio State University, 2001; Roberts and Janovy, 2000)

Reproduction

The gravid proglottid detaches from the adult and ruptures, thereby releasing eggs into the feces of the definitive host. The intermediate host ingests eggs in contaminated food or water. The egg hatches to an oncosphere which develops into a unilocular hyatid cyst. Daughter cysts bud from the inner walls of the cyst via asexual reproduction, giving rise to numerous juveniles called protoscolices. Canids eat the intermediate host and hence acquire the protoscolices which develop to adults. (Ohio State University, 2001; Roberts and Janovy, 2000)

  • Key Reproductive Features
  • simultaneous hermaphrodite
  • sexual
  • asexual
  • Parental Investment
  • no parental involvement

Behavior

Oncospheres in the intermediate host's intestine penetrate the mucosa using its six little hooks. They enter a portal venule and may end up in any organ, most commonly in the lung or liver and develops slowly into a unilocular hydatid cyst. When the cyst is eaten by the definitive host, the protoscolices evaginate and attach to the villi in the small intestine. It takes about 56 days to become an adult. (Kearn, 1998; Roberts and Janovy, 2000)

Communication and Perception

Cestodes in general have sensory organs in the scolex, which are attached to longitudinal nerves extending down the body. The nerves are attached to organs and the cestodes can detect tactile stimulation. (Brusca and Brusca, 2003)

Food Habits

The adult Echinococcus granulosus is parasitic on canids, the definitive hosts. Nutrients are absorbed across the worm's tegument. Many mammals may be intermediate hosts, especially herbivores. (Roberts and Janovy, 2000)

  • Animal Foods
  • body fluids

Predation

These animals are probably not preyed on directly but are ingested. Egg and larval mortality are high due to the parasite not reaching appropriate hosts.

Ecosystem Roles

Echinococcus granulosus parasitizes canines such as dogs, wolves or dingos. It can also be found in lions. Intermediate hosts include sheep, moose, wallabies, camels, warthogs, and reindeer.

Species Used as Host

Economic Importance for Humans: Negative

In humans, Echinococcus granulosus is the most common agent of cystic hyatid disease. Cysts may be asymptomatic for years, but pressure of the cyst on surrounding tissues or bones may lead to blindness, collapse of infected bones, or even sudden death if the cyst is in the heart. If a cyst ruptures the host may get anaphylactic shock, a hypersensitive reaction to a flood of foreign material in the body that results in death. Treatment for this disease often involves removal of the cyst via major surgery. (Lightowlers et al, 2000) (Lightowlers, et al., 2000)

Conservation Status

Contributors

Renee Sherman Mulcrone (editor).

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

Glossary

Australian

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

World Map

Ethiopian

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

World Map

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.

World Map

Neotropical

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

World Map

Palearctic

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

World Map

agricultural

living in landscapes dominated by human agriculture.

asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

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 disease in humans

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

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.

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

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.

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.

World Map

parasite

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

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.

tactile

uses touch to communicate

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

Arambulo, P. 1997. Public health importance of cystic echinococcus in Latin America. Acta Tropica, 67: 113-124.

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

Eckert, J., F. Conraths, K. Tackmann. 2000. Echinococcus: an emerging or re-emerging zoonosis. International Journal for Parasitology, 30: 1283-1294.

Kearn, G. 1998. Parasites and the Platyhelminthes. London: Chapman and Hall.

Lightowlers, M., A. Flisser, C. Gauci, D. Heath, O. Jensen. 2000. Vaccination against cysticercosis and hyatid disease. Parasitology Today, 16(5): 191-196.

Ohio State University, 2001. "Echinococcus granulosus" (On-line). Parasites and parasitological Resources. Accessed October 13, 2004 at http://www.biosci.ohio-state.edu/~parasite/echinococcus.html.

Roberts, L., J. Janovy. 2000. Foundations of Parasitology Sixth Edition. New York: McGraw Hill.

Wardle, R., J. McLeod, S. Radinovsky. 1974. Advances in the Zoology of Tapeworms, 1950 - 1970. London and Delhi: Oxford University Press.

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