Beef Tapeworm - Taenia Saginata

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Taenia saginata Beef Tapeworm Page 1

Notes in Microbiology

The Beef Tapeworm - Taenia saginata

Taenia saginata

Scientific classification

Kingdom: Animalia

Phylum: Platyhelminthes

Class: Cestoda


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Taenia saginata, also known as Taeniarhynchus saginataor the beef tapeworm, is a parasite of

both cattle and humans, causing taeniasis in humans. Taenia saginataoccurs where cattle are raised by

infected humans maintaining poor hygiene,humanfeces are improperly disposed of, meat inspection programs

are poor, and where meat is eaten without proper cooking. The disease is relatively common In Africa, some

parts of Eastern Europe, Southeast Asia, and Latin America.

Description

Taenia saginataproglottid stained to show uterine branches. The pore on the side identifies T. saginataas

a cyclophyllidcestode.

Order: Cyclophyllidea

Family: Taeniidae

Genus: Taenia

Species: T. saginata

Binomial name

Taenia saginata

Goeze, 1782


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T. saginatais normally 4 m to 10 m in length, but can become very large, over 12 m long in some

situations. The body is whitish in colour, divided into the anteriorscolex, followed by a short neck and a highly

extended body proper called the strobila. Unlike other tapeworms, the scolex does not have a rostellum or

scolex armature. It is composed of four powerful suckers. The strobila is composed a series of ribbon-like

segments called proglottids. The segments are made up of mature and gravid proglottids. T. saginatais the

largest of genusTaenia, consisting between 1000 to 2000 proglottids, and can also have a lifespan of 25 years

in a host's intestine.[2]

The mature proglottid contains the uterus (unbranched), ovary, genitalpore, testes,

and vitelline gland. It does not have a digestive system, mouth, anus, or digestive tract. It is also

an acoelomate, meaning it does not have a body cavity. In thegravid proglottid, the uterus is branched and

filled with eggs. The gravid segments detach and are passed in the feces. Each of these segments can act as

a worm. When they dry up, the proglottid ruptures, and the eggs are released. The egg can only infect cattle,

the intermediate host. Inside the cow's duodenum, the oncosphere hatches with the help of

the gastric and intestinal secretions, and migrates through the blood to the muscle. There it develops intoinfective cysticercoid cysticerci.

[3]

Life cycle


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The life cycle of Taenia saginata

The life cycle is indirect and complicated, and is completed in humans as the definitive host and cattle

as the intermediate host. The adult worm inhabits the small intestine of humans. Fertilized eggs are released

through the faeces along with the gravid proglottidwhich gets detached from the strobila. Cattle ingest the

infective embryo while grazing. Thedigestive enzymes will break the thick shell of the egg and allow formation

of the zygotescalled "oncospheres". These zygotes then penetrate the mucous layer of the diges tive tract and

enter the circulation of the host. This is where the young larval stages form a pea-sized, fluid filled cyst, also

known as Cysticercus bovis and these cysts seem to form in the muscular fibers and are sometimes seen in

specific organs like the lungs and liver. Humans acquire the infective larvae from eating undercooked meat

i.e.,measley beef. Thedigestive enzymes break down the cysticercus and the larval cyst is released and the

inverted scolex is able to come out and attach to the hosts intestine. Adult tapeworm take about 2 months to

develop, and within three months it can reach 5 m long.[2]

Epidemiology

The disease is relatively common in Africa, some parts of Eastern Europe, the Philippines, and Latin

America.[1]

Humans become infected when they eat undercooked beef. Prevention is easy; cook beef until it is

no longer pink inside and 56C in the center, because this kills the cysticerci. Also, beef frozen at -5C is

considered to be safe to consume.

This parasite is found anywhere where beef is eaten, even in countries such as the United States, with

strict federal sanitation policies. In the US, the incidence of infection is low, but 25% of infected cattle are still

sold.[3]

Symptoms

Tapeworms are usually asymptomatic. However heavy infection often results in weight

loss, dizziness, abdominal pain, diarrhea,headaches, nausea, constipation, or chronic indigestion, and loss

of appetite. There can be intestinal obstruction in humans and this can be alleviated by surgery. The tapeworm

can also expel antigens that can cause an allergic reaction in the individual.[3]

Diagnosis


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The basic diagnosis is done from a stool sample. Feces are examined to find parasite eggs. The eggs

look like other eggs from thefamilyTaeniidae, so it is only possible to identify the eggs to the family, not to the

species level. Since it is difficult to diagnose using eggs alone, looking at the scolex or the gravid proglottids

can help identify it as Taenia saginata.[3]

Proglottids sometimes trickle down the thighs of infected humans and

are visible with unaided eye, so can aid with identification. Observation of scolex help distinguish between T.

saginata, T. soliumand T. asiatica. When the uterus is injected with India ink, its branches become visible.

Counting the uterine branches enables some identification (Taenia saginatauteri have 12 or more branches on

each side, while other species such as Taenia soliumonly have five to 10).[1]

Differentiation of the species from other species of Taenia, such as T. soliumand T. asiatica, is

notoriously difficult because of their close morphological resemblance, and their eggs are more or less

identical. Identification often requires histological observation of theuterine branches and PCR detection

of ribosomal 5.8S gene.[4]

T. saginatas uterus stems out from its center to form 12 to 20 branches, but in

contrast to its closely related Taeniaspecies, the branches are much less in number and comparatively thicker;

in addition, the ovaries are bilobed and testes are twice as many.[5]

Eosinophilia and elevated IgE levels are chief hematological findings.

Treatment

Treatment for cestode infection with the drug praziquantel opens membrane calcium channels,

causing paralysis of the worm, thus aiding the body in expelling the parasite through peristalsis. Niclosamide,

used to treat many different kinds of infections withtrematodes and adult tapeworms, is also quite effective.

Prevention

Adequate cooking (56C for 5 minutes) of beef viscera destroys cysticerci. Refrigeration, freezing (-10C for 9

days) or long periodsalting is lethal to cysticerci. Inspection of beef and proper disposal of human excreta are

also important measures.


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References:

1. âbc

Lange Microbiology, Chapter 46. Medical Parasitology.

2. âb

Bogitsh BJ, Carter CE (2005). Human Parasitology, 3rd Edition. Academic Press, pp. 273-

277. ISBN 0-12-088468-2

3. âbcde

Roberts L, Janovy JrJ, Schmidt GD (2005). Foundations of Parasitology (8th

edn). McGraw-Hill Companies, Inc., New York.ISBN 0-07-128458-3

4. ^ Gonzlez LM, Montero E, Harrison LJ, Parkhouse RM, Garate T. (2000). "Differential diagnosis

of Taenia saginata and Taenia solium infection by PCR." . J Clin Microbiol.38 (2): 737

744. PMC86191. PMID10655377.

5. ^ Zarlenga DS. (1991). "The differentiation of a newly described Asian taeniid from Taenia saginata

using enzymatically amplified non-transcribed ribosomal DNA repeat sequences.". Southeast Asian J Trop

Med Public Health.22 (suppl): 251255. PMID1822899.

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Beef Tapeworm - Taenia Saginata