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Taenia saginata (Pathogen Intestinal Cestode)

Organism:

T. saginata was apparently differentiated from T. solium in the late 1700s;

however, cattle were not identified as the intermediate host until 1863. Thisinfection has a worldwide distribution and is generally much more common than

T. solium infection, particularly in the United States. The overall impact on

human health is much less than that seen with T. solium, since cysticercosis

with T. saginata is apparently quite rare.

Taenia saginata gravid

proglottidT. saginata scolex Taenia spp. egg

Life Cycle:

The life cycle is very similar to that ofT. solium. Infection with the adult worm is

initiated by the ingestion of raw or poorly cooked beef containing encysted T.

saginata larvae. As with T. solium, the larva is digested out of the meat in the

stomach, and the tapeworm evaginates in the upper small intestine and

attaches to the intestinal mucosa, where the adult worm matures within 5 to 12

weeks. The adult worm can reach a length of 25 m but often measures only

about half this length. The scolex is ``unarmed'' and has four suckers with nohooks. The proglottids usually number 1,000 to 2,000, with the mature

proglottids being broader than long and the gravid proglottids being narrower

and longer. Although a single worm is usually found, there can be multiple worms

present (personal observation).

Acquired:

Infection in humans is acquired through ingestion of cysticerci within raw or rare

beef. Other animals found to harbor cysticerci include buffalo, giraffe, llama, and

possibly reindeer. Actual cases of human cysticercosis with T. saginata are rare

in the literature, and there is speculation that some reported cases have been

inaccurately diagnosed.

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Epidemiology:

Worldwide, primarily human to human transmission

Clinical Features:

Few symptoms are associated with the presence of the adult worm in the

intestine. Although rare symptoms (obstruction, diarrhea, hunger pains, weight

loss, or appendicitis) have been reported, the most common complaint is the

discomfort and embarrassment caused by the proglottids crawling from the

anus. This occurrence may be the first clue that the patient has a tapeworm

infection. Occasionally, the proglottids are also seen on the surface of the stoolafter it is passed.

Clinical Specimen:

Stool: The standard O&P examination is the recommended procedure for

recovery and identification ofTaenia spp.eggs in stool specimens, primarily

from the wet preparation examination of the concentration sediment. Since the

eggs ofT. saginata and T. solium look identical, identification to the species

level is normally based on the recovery and examination of gravid proglottids.

Adult worms: Gravid proglottids may be recovered in stool; often they can be

seen lying on the top or bottom of the stool specimen submitted as a fresh

specimen. Occasionally, only the proglottid may be submitted fresh or in

preservative.

Laboratory Diagnosis:

Stool: The standard O&P examination is the recommended procedure for

recovery and identification ofTaenia spp.eggs in stool specimens, primarily

from the wet preparation examination of the concentration sediment. The eggs

are most easily seen on a direct wet smear or a wet preparation of the

concentration sediment.

Adult worms: Identification to the species level is normally based on the

recovery and examination of gravid proglottids, in which the main lateral

branches are counted (count on one side only; 15 to 20 forT. saginata and 7 to

13 forT. solium). Often the gravid proglottids of T. saginata are somewhat

larger than those of T. solium; however, this difference may be minimal or

impossible to detect. If the scolex is recovered after therapy (which may requirepurgation), there will be four suckers and no hooks. Preliminary examination of

the gravid proglottid may not allow identification without clearing or injection of

the uterine branches with India ink.

Note Since there is always the possible danger that the proglottid is T. solium,

with the inherent problem of egg ingestion and cysticercosis, all specimens

should be handled with extreme caution.

Organism Description:

Egg: The eggs are usually spheroidal and are yellow-brown in color. They are

thick-shelled eggs, measuring 31-43 m; they will contain a six-hooked

oncosphere (embryo). The eggs are routinely found in the stool, even if gravid

proglottids are not found in the specimen.Adult worm: The adult tapeworm is comprised of the attachment organ (scolex),

to which is attached a chain of segments or proglottids called the strobila. Each

proglottid contains a male and female reproductive system. The proglottids are

classified as immature, mature, or gravid. The gravid proglottids are found at

the end of the strobila and contain the fully developed uterus full of eggs. The

branched uterine structure in the gravid proglottids is often used as the main

criterion for identification of the organism to the species level. The scolex and

eggs can also be used to identify a cestode to the species level. Often the adult

worms can reach about 15 - 20 ft in length and may survive for up to 25 years.

The scolex of T. saginata is quadrate shaped, has four suckers, and no

rostellum or hooklets. The gravid proglottids can be found in feces and are

longer than wide (19 x 17 mm) with 15-20 lateral branches on each side of thecentral uterine stem. They usually appear singly and can actively crawl like an

inchworm - they may actually migrate under a fresh stool specimen.

Laboratory Report:

Taenia spp.eggs present

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Taenia saginata gravid proglottid

Proficiency Testing: Note: In Proficiency Testing specimens, the eggs may

be harvested from gravid or mature proglottids. In some cases the eggs may

contain a gelatinous coating that may be somewhat confusing. This coating is

generally found on eggs that have been recovered from the mature proglottids

and not from the gravid proglottids at the end of the strobila. Dont let this extra

coating confuse you; the six-hooked embryo can still be seen within the egg

shell. The true tapeworm egg will have a radially striated shell that is relatively

thick.

Treatment:

Garcia, L.S. 2007. Diagnostic Medical Parasitology, 5th ed., ASM Press,

Washington, D.C.

Control:

Cattle should not be allowed to graze on ground contaminated by human

sewage.

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