Download The Pork Tapeworm Taenia solium

The Pork Tapeworm
Taenia solium
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Appearance and General Information
The pork tapeworm is a flatworm, belonging to the phylum
Platyhelminthes.
It is one of the most potentially dangerous adult tapeworms to
humans. 3
Its body is white and ribbon like. 5
It is about 6 mm wide, 4 and usually 2
to 3 metres long, but some specimens
can reach over 9 metres. 3
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Parts of the Tapeworm
Taenia solium has 3 main body parts:
1.
2.
3.
The head (scolex)
A neck
An elongated body (the
strobilia)
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Tapeworm Scolex
The Scolex
The scolex of the tapeworm is spheroid
and about 1 mm in diameter. It has 4
suckers surrounding the rostellum
(mouthparts), for attachment. 5
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The Strobilia
The strobilia is divided into 800 – 900 segments, called
proglottids. Growth occurs from the neck, so the oldest
segments, known as gravid proglottids, are at the posterior
end of the tapeworm. 5
The Life Cycle of Taenia solium
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Life Cycle in Humans
Humans are the primary hosts, so they are infected with the adult
stage of the tapeworm. Infection occurs when a person eats
‘measly’ pork infected with the tapeworm larvae.
The larvae, called cysticerci, are small oval capsules, containing an
inverted scolex. When stimulated by stomach enzymes, the scolex
pops out and anchors to the wall of the small intestine, and the
strobilia begins to grow. 5 It takes between 5 and 12 weeks for the
tapeworm to mature. 3
A cysticercus
Adult tapeworms may live for up to 25 years. 4
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Reproduction
The pork tapeworm is a hermaphrodite, which means it can selffertilise. 5 Each proglottid contains male and female organs which
fertilise each other. A gravid proglottid may contain up to 50,000
eggs. 5
The eggs pass out in the faeces, either
individually or in the proglottids. They can
survive in the environment for up to 2
months. 5
A Taenia solium egg
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Life Cycle in Pigs
Pigs are the intermediate, or secondary hosts. They
become infected when they ingest eggs in human faeces
or infected vegetation. Once inside, the tapeworm eggs
hatch into motile larvae (oncospheres) and attach to the
intestinal wall. 5 The larvae penetrate the intestine and
travel through blood and lymphatic vessels to various
organs in the body, particularly to the muscles, brain
tissue and the liver. 5
In these areas they form cysts, called
cysticerci, around 1 to 2 cm in diameter.
This takes around 70 days, however the
cysts continue to grow for up to a year. 5
The cysticerci then remain dormant
unless the infected pork is eaten by
humans.
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-pig.jpg
Measly Pork
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pork-cysts.jpg
Humans as Intermediate Hosts
Humans can accidentally become the secondary hosts, either by
autoinfection, where tapeworm eggs hatch inside the intestine, or
by eating food contaminated with tapeworm eggs. 5 If this
happens, cysts will form inside the person. The cysticerci can form
in nearly any tissue or organ, but are usually found in
subcutaneous connective tissue, the eye, the brain, or in the heart,
liver or lungs. 3
Cysts in the Brain
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Problems Caused by Cysts
When a cysticercus dies, it can cause a severe inflammatory
response, which may be fatal to the host, particularly if it is in the
brain. 3
Dead cysts are slowly calcified, which is particularly devastating for
ocular cysts. 3
In rare cases, a cyst may become prolific, and develop branching
extensions. This can cause tumor-like growths. 4
Symptoms
Taeniasis (infection by the adult tapeworm)
Taeniasis does not usually show any symptoms; however in severe
cases intestinal irritation, anaemia and indigestion can result. 5
Cysticercosis (infection by the larval stage)
Cysticercosis is much more severe than taeniasis. Cysts in the brain
(neurocysticercosis) may cause epilepsy, severe headaches,
blindness and even death. 6 In the eye, cysts can cause irreparable
damage to the retina. 3 When in the muscle, skin or liver, there are
few effects, however in some cases subcutaneous nodules may
develop. 3 Symptoms may take several years to appear. 5
Facts and Statistics
• Neurocysticercosis is the most frequent preventable cause of
epilepsy worldwide (World Health Organisation 2015)
• Neurocysticercosis causes up to 50,000 death per year
(Encyclopedia of Life n.d.)
• Up to 20 million people worldwide are infected with pork
tapeworm cysticerci (Encyclopedia of Life n.d.)
• Taeniasis affects up to 50 million people worldwide (Standford
University 2004)
Where It Is Found
Taenia solium is found worldwide, wherever pork is eaten. Human
infection mostly occurs in areas where people eat undercooked
pork and live in close contact with pigs, i.e. areas like West Africa,
South East Asia, India, Mexico and Latin America. 5
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Map Showing Countries at Risk of Cysticercosis
http://gamapserver.who.int/mapLibrary/Files/Maps/Global_cysticercosis_2009.png
How Humans Encounter It
People become infected by the tapeworm when they consume
‘measly pork’ - undercooked pork that contains cysts.
Infection by cysticerci can occur either by autoinfection, where
tapeworm eggs hatch inside the intestine, or by consumption of
food or water contaminated with tapeworm eggs. 5
Prevention
Prevention in Pork
Pigs should be kept away from human faeces. Untreated human
sewage should not be used as fertiliser for crops.
Prevention in Humans
High standards of personal hygiene are very important to prevent
tapeworm eggs being ingested by humans.
Tapeworm cysts in pork can be killed by either cooking the meat
thoroughly, or by freezing at -10°C for 5 days. 1
Treatment
Praziquantel is the most effective drug used to treat taeniasis,
however Niclosamide can also be used. 5
As the death of cysts causes an inflammatory response, treatment
of cysticercosis varies, and may include: long term courses with
Albendazole and/or Praziquantel, in addition to supporting therapy
with corticosteroids and/or epilepsy preventing drugs. Surgery is
often successful in removing cysts. 6
There is no standard treatment for neurocysticercosis; treatment is
tailored to the individual’s situation. 6
Bibliography
1. Centers for Disease Control and Prevention 2014, Parasites - Cysticercosis, viewed 31
August 2015, http://www.cdc.gov/parasites/cysticercosis/.
2. Medline Plus 2015, Tapeworm - beef or pork, viewed 31 August 2015,
https://www.nlm.nih.gov/medlineplus/ency/article/001391.htm.
3. Schmidt, G & Roberts, L 1989, Foundations of Parasitology (4th ed), Times
Mirror/Mosby College Publishing, St Louis.
4. Stanford University n.d., Taenia Solium, viewed 1 September 2015,
http://web.stanford.edu/group/parasites/ParaSites2001/taeniasis/solium2.html.
5. Wikipedia 2015, Taenia solium, viewed 26 August 2015,
https://en.wikipedia.org/wiki/Taenia_solium.
6. World Health Organisation 2015, Taeniasis/Cysticercosis, viewed 27 August 2015,
http://www.who.int/mediacentre/factsheets/fs376/en/.
7. Encyclopedia of Life n.d., Taenia solium, viewed 8 September 2015,
http://eol.org/pages/3247842/overview.