Taenia saginata

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Geographic Range

In the past, Taenia saginata has been reported in Asia, Europe, Africa, and North and South America. The prevalence of Taenia saginata is measured by the occurrence of its infection in man and cattle. The infection in humans, taeniasis, is not a disease that is required by law to report; thus, the prevalence of T. saginata in man is measured by the quantity of drugs sold to combat infection. One estimate proposed nearly 40 million human infections globally: 100,000 in North America, 700,000 in Central and South America, and the majority in Asia and Africa. Within Europe, Slovakia and Turkey have reported the highest prevalence rates of taeniasis. This estimate proposed less than a one percent prevalence rate in the United States compared to 50 percent in East Africa. The infection in cattle, bovine cysticercosis, is usually monitored by postmortem meat inspections. (Dorny and Praet, 2007; Hoberg, 2002; Markell, et al., 1999; Scandrett, et al., 2009; Stoll, 1947)

Habitat

Typically, T. saginata eggs hatch in the gastrointestinal tract of cattle. The embryo, called an oncosphere, moves through the lining of the gut to infect cardiac and skeletal muscles via the circulatory system. The larval stage of the tapeworm, known as a metacestode, develops in the muscles and sometimes the brain. The metacestode reaches adulthood in the small intestine of humans. Eggs, which exit the host through the anus, typically remain in sewage or on land if sewage is used for irrigation. Eggs tend to survive longer in areas such as grass, as long as it is moist so the eggs avoid dessication. (Beaver, et al., 1984; Despommier, et al., 2000; Dorny and Praet, 2007; Froyd, 1962; Greenberg and Dean, 1958; Ito, et al., 2003; Scandrett, et al., 2009; White and Weller, 2001)

Physical Description

The flexible adult tapeworm’s head, or scolex, has four muscular suckers for attaching to the upper jejunum (middle section of the small intestine) of its host, but no hooks on the anterior extension of the scolex, termed the rostellum. The absence of hooks on the rostellum has earned another name for the species, the “unarmed tapeworm.” Taenia saginata can be distinguished from its sister species, Taenia solium, by the absence of these rostellar hooks on the scolex. A neck about half as wide as the scolex, separating the head from the rest of the body, is where new proglottids are formed that together make up the flattened, segmented body called the strobilus. The thousands of proglottids of the strobilus make T. saginata one of the largest human parasites; generally this species is less than five meters long, but has been observed to grow to 25 meters. When the proglottids mature they contain both the male and female reproductive organs. When the proglottids are gravid, they contain a number of uterine branches that pass eggs and can serve as an identifying characteristic of T. saginata; the gravid proglottids of T. saginata have 12 or more uterine branches while its sister species, T. solium, has 10 or fewer. Another characteristic of this species is the genital pore on the side of the proglottids as opposed to the middle in T. solium. The body surface of proglottids are surrounded in a tegument that aids in the absorbtion of nutrients by the use of tiny folds called microvilli. The eggs are usually 30 to 40 micrometers and surrounded by a striated brown shell. The egg contains the embryo, an oncosphere, that gives rise to the metacestode larva. The six-hooked larva, termed a hexacanth, hatches from the egg and develops into a cysticercus. Cysticerci are white, oval-shaped, fluid-filled, generally between 7 to 10 millimeters long, 4 to 6 millimeters wide and have an invaginated scolex. (Abuladze, 1964; Beaver, et al., 1984; Despommier, et al., 2000; Dorny and Praet, 2007; Flisser, 1994; Greenberg and Dean, 1958; Hoberg, 2002; Ito, et al., 2004; Ito, et al., 2003; Markell, et al., 1999; Mayta, et al., 2000; Scandrett, et al., 2009; White and Weller, 2001)

  • Range length
    25 (high) m
    82.02 (high) ft

Development

The indirect life cycle of T. saginata requires the transmission of its eggs and cysticerci between the predator-prey interaction of its definitive human host and its intermediate cattle host. The development of T. saginata begins in the small intestine of cattle when the oncosphere hatches from an egg after it has been ingested. The eggs hatch in the intestinal tract of cattle because the cow’s digestive enzymes are able to break down the cyst wall. The hexacanth larva moves through the intestinal lining into the blood stream where it migrates to muscle tissue and forms a cyst. The cysticercus then grows for approximately 10 to 12 weeks, after which it is infective to humans. Human ingestion of undercooked meat infected with a cyst can allow the cysticercus to develop into an adult, which usually takes around two to three months. During this time the hooks are lost from the scolex and new proglottids develop from the neck, elongating the strobilus. As the proglottids mature they move further from the scolex and when they become gravid they are able to release eggs. Motile, gravid proglottids detach from the adult and pass, along with their eggs, through the stool to their environmental reservoir. (Beaver, et al., 1984; Despommier, et al., 2000; Froyd, 1962; Greenberg and Dean, 1958; Hoberg, et al., 2000; Hoberg, 2002; Loos-Frank, 2000; Markell, et al., 1999; Scandrett, et al., 2009; White and Weller, 2001)

Reproduction

When immature proglottids mature they are hermaphroditic, or monoecious, and can fertilize adjacent segments or occasionally self-fertilize. (Despommier, et al., 2000)

Taenia saginata uses both sexual and asexual modes of reproduction: the scolex reproduces asexually by budding and the proglottids that contain both male and female reproductive organs reproduce sexually. Immature proglottids take around 10 to 12 weeks to mature, and during this time the male reproductive organ develops between 300 and 400 testes. Each gravid proglottid can produce and release hundreds of eggs per day and the thousands of proglottids of an adult can release millions of eggs in a day. These tapeworms have evolved such a high reproductive potential because their indirect life cycle can be interrupted at many stages: human feces do not often pollute cattle water or feed, few eggs are taken up to infect cattle, and cysticeri are often killed by properly cooking the beef. The life cycle of T. saginata is rare among helminths as it relies on humans as its sole definitive host. (Beaver, et al., 1984; Despommier, et al., 2000; Greenberg and Dean, 1958; Markell, et al., 1999; Scandrett, et al., 2009; White and Weller, 2001)

  • Breeding interval
    daily
  • Range number of offspring
    1000 to 2000000

There is no parental investment after the gravid proglottids detach from the adult strobilus. The proglottids leave the intestine and exit the host through the anus. (Dorny and Praet, 2007; Scandrett, et al., 2009)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

Generally, adult T. saginata can survive for several years in their human host. However, they have been known to survive for 20 to 25 years in certain cases. Eggs can persist in sewage for a little over two weeks, but for around five months on grass in an open environment if they avoid desiccation. Cysticerci typically persist in cattle for a few months, sometimes over nine, before they deteriorate. (Beaver, et al., 1984; Despommier, et al., 2000; Dorny and Praet, 2007)

  • Range lifespan
    Status: wild
    20 to 25 years
  • Typical lifespan
    Status: wild
    2 to 5 years

Behavior

The adults develop and remain in their human host their entire life, constantly absorbing food from the nutrient baths of the human’s meals. The individual proglottids that release from the adult after they are gravid are motile and actively leave the host through the anus, more often during times when the host is active. Every proglottid has longitudinal and transverse muscle, giving the adult horizontal and vertical motility and each segment mobility as well. An adult is typically found as the sole parasite in a human, most likely because supporting more than one tapeworm would put too much stress on the definitive host. (Beaver, et al., 1984; Despommier, et al., 2000; Dorny and Praet, 2007; Markell, et al., 1999)

Communication and Perception

Each proglottid has a simple nervous system consisting of only nerves, while the scolex of the tapeworm has a slightly more complex nervous system in which nerves end in ganglia. In the closest resemblance of communication between T. saginata, adult tapeworms excrete molecules that deter other parasites from co-infecting the same host. This increases the likeliness of survival for the tapeworms by preventing too much stress on the host. (Despommier, et al., 2000)

Food Habits

Taenia saginata does not have a digestive system, instead each proglottid is able to absorb pre-digested host nutrients aided by its specialized skin; the microfolds of the tegument increase the absorbing surface area. (Beaver, et al., 1984; Despommier, et al., 2000; Markell, et al., 1999)

  • Animal Foods
  • body fluids

Predation

There are no known predators of Taenia saginata.

Ecosystem Roles

Taenia saginata is a worldwide obligate endoparasite; the adults live in the human intestine and the cysticercus larva usually inhabits the muscles of ungulates, primarily cattle. Although T. saginata is known as the beef tapeworm, only the juvenile and not the adult stage has been discovered in cattle. (Dorny and Praet, 2007; Hoberg, 2002; Scandrett, et al., 2009)

Species Used as Host
  • Humans, Homo sapiens are the definitive hosts
  • Cattle, Bos primigenius are the primary intermediate hosts

Economic Importance for Humans: Positive

There is no known economic benefit of Taenia saginata to humans. Compared to T. saginata's sister species, T. solium, T. saginata is of little medical importance. (Dorny and Praet, 2007; Hoberg, 2002)

Economic Importance for Humans: Negative

Taenia saginata is seen as a human health hazard and is recognized to cause serious economic losses to the cattle industry around the world. Taeniasis of humans has mainly been reported to cause abdominal pain, nausea, diarrhea, and weight loss, while bovine cysticercosis of cattle typically warrants infected cattle to be either refrigerated for a period of time to kill the parasites, partitioned to keep the uninfected portions, or simply condemned from human consumption. In the United States alone, it is estimated that cysticercosis causes more than two billion dollars in production losses of domestic food animals annually. (Despommier, et al., 2000; Fan and Chung, 1995; Fan, 1997; Hoberg, 2002)

Conservation Status

Rather than conservation efforts, eradication efforts are underway to stop the transmission of the human parasite. Attempts to control and eliminate taeniasis usually interrupt the links between the hosts of the tapeworm via systematic meat inspections and regulations on the treatment and use of sludge from sewage water. Cattle older than six weeks are inspected for cysticercosis in skeletal and cardiac muscles; a generalized infection of the carcass is deemed unacceptable for human consumption, but a localized infection can be refrigerated for a period of time to be rendered safe. In spite of these examination efforts, taeniasis and bovine cysticercosis occupy a large geographical range. (Dorny and Praet, 2007; Scandrett, et al., 2009)

Other Comments

Besides bovine cysticercosis the infection in cattle is also known as bladder worm. Before the infection in cattle was known to be a larval stage of Taenia saginata, the juvenile was given its own genus, Cysticercus bovis. (Beaver, et al., 1984; Despommier, et al., 2000; Markell, et al., 1999)

Contributors

Austin Payne (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

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.

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.

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.

chemical

uses smells or other chemicals to communicate

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.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body

introduced

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

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

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

protandrous

condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

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

solitary

lives alone

sperm-storing

mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.

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.

year-round breeding

breeding takes place throughout the year

References

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