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Taenia saginata
Scolex Whole worm
The beef tapeworm, Taenia saginata Goeze, 1782 was widely known in ancient
Egypt and Greece and was prevalent in Europe. Leuckart in 1862 first
demonstrated that human infection resulted from eating infected raw beef. Beef
tapeworm infection is cosmopolitan among beef-eating peoples.
Morphology, Biology and Life Cycle
The adult worm develops typically in the middle third of the small intestine,
attached to the mucosa. The average length of the relaxed worm is approximately 5
meters, although there are records of specimens of far greater lengths. There are
1000 to 2000 proglottids, of which form one-third to one-half are gravid. Usually
only a single specimen occurs in an infection, but there may be two or more.
The fully developed worm is delicate anteriorly and more robust posteriorly. The
rhomboidal scolex. Instead of hooklets on a rostellar prominence as in Taenia
solium there is a slight apical depression. The terminal proglottids become
separated from the strobila and actively migrate out of the bowel or are evacuated
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in the stool with only partial loss of eggs, which are essentially spherical, measure
31 to 43 microns in diameter, have a thin, transparent outer envelope.
The evacuated gravid segments extrude the eggs; disintegrate on moist earth or in
sewage, freeing the eggs which are ready for development in the intermediate host.
Cattle grazing on infested ground pick up the eggs, which hatch in duodenum. The
emerging embryos reach skeletal muscles or the heart, where they transform in 60
to 75 days into the typical cysticercus stage (Cysticercus bovis). Thereafter, for a
period of more than a year persons who eat the raw infected beef are subject to
infection. In 3 to 6 months after human exposure the complete worm has
developed and gravid proglottids are being shed.
Pathogenicity and Symptomatology
Infection with T. saginata is ordinary symptomless and except for the discomfort,
inconvenience or embarrassment resulting gravid proglottids crawling out of the
anus. However, towards the end of the prepatent period there are sometimes
diarrhea, and abdominal cramps, and moderate loss of weight. Appendicitis due to
the lodging of gravid proglottids in the appendiceal lumen has been reported.
Rarely a mass of tangled worms may cause acute intestinal obstruction.
Diagnosis
Eggs of T. saginata are often found in the feces. They are indistinguishable from
those of T. solium. In all mature infections gravid proglottids are being evacuated.
The unpreserved proglottids have number of main lateral arms of the uterus (15 to
20, usually 18) on each side of the main uterine stem. The constitutes specific
diagnosis. The gravid proglottids deposit eggs in the anus and perianal area as they
crawl from the rectum. For this reason the diagnosis may be made by use of an
adhesive cellophane tape technique, as with enterobiasis.
Epidemiology
Cattle acquire the larval stage of T. saginata by grazing on moist pasture land
polluted by feces containing the fully embryonated eggs of this tapeworm.
Under suitable conditions of moisture and temperature the eggs may remain viable
for 6 months. Approximately 2 to 3 months after the cattle are exposed the larva
have matured and the meat is infective. After a year or more, however, they often
become calcified. In some human communities infections results from eating
frankly raw beef. In most endemic it is due to consumption of undercooked steaks
or burgers.
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Control
Basically, control of teniasis consists in sanitary disposal of human feces, so that
eggs of T.saginata in excreta or community sewage do not reach pastures where
cattle graze. Beef which has been kept 24 hours or longer in a deep freezer is
sterilized. Likewise, heating the meat to 65° C is a safeguard.
Taenia solium
Mature proglottids Scolex
The larval stage of the pork tapeworm (Cysticercus cellulosae) was described from
swine by Greek naturalists. Pork tapeworm infection is cosmopolitan wherever raw
or inadequately processed pork is eaten.
Morphology, Biology and Life Cycle
In most respects, Taenia solium resembles T.saginata, but T.solium is shorter,
usually having a length of less than 3 meters, due to a smaller number of
proglottids (fewer than 1000) and shorter gravid proglottids. There is a double
circle of alternating large and small hooklets. Eggs of T. solium are
indistinguishable from those of T. saginata.
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Gravid proglottids passed in the stool or actively migrating out of the anus of the
host discharge the eggs or disintegrate when deposited on the ground. To develop,
the eggs must be ingested by hogs. The embryos reach skeletal muscle and
myocardium. Here they transform in 2 to 3 months into cysticercus larvae
(Cysticercus cellulosae).
When human eat pork containing viable cysticerci, the larvae are digested out of
the meat, the heads become attached to the walls of the proximal portion of the
ileum and in approximately 3 months each develops into a complete worm.
Pathogenicity and Symptomatology
The adult T. solium in the human small intestine produces the same pathological
processes and clinical manifestation as T. saginata. However, because of its shorter
length there is less likelihood that intestinal obstruction will develop.
Diagnosis
Although eggs of T.solium are occasionally found in the host's stools or in anal
swabs, a specific diagnosis is based on demonstration of the relatively small
number of main lateral arms of the uterus (7 to 13, usually about 9) in gravid
proglottids compressed between two glass slides.
Treatment
Treatment of taeniasis may include administration of praziquantel (5-10 mg/kg,
single-administration) or niclosamide (2 g, single-administration, followed after 2
hours by a laxative).
Epidemiology
Human infection with the adult Taenia solium results from eating essentially raw
pork containing viable Cysticercus cellulosae. The hog is the usual source from
which man obtains the larval stage, and man is the only natural host of the adult
worm. However, man is also a suitable host for the cysticerus.
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Control
The serious, frequently disabling and at times fatal consequences of human
cysticercosis resulting from larval T.solium infection indicate the peculiar need for
control of this infection. In endemic areas human feces should not be deposited in
locations where hogs have access to them.