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COMMON INTESTINAL WORMS
FOUND IN SOUTHERN AFRICA -
CESTODES AND TREMATODES
#204
Prof. M A Kibeland
D Hanslo
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QUESTION 1
How do cestode worms differ from the roundworms?
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ANSWER 1
As a group they are:
– flat worms
– hermaphrodites (both sexes in same worm)
– have no body cavity
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QUESTION 2
Which species of cestode are important clinically in
Southern Africa?
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ANSWER 2
The most important is the pork tapeworm, or Taenia
solium. Others which are also found are Taenia saginata
(beef tapeworm) and Echinococcus, the cause of hydatid
disease.
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QUESTION 3
What do tapeworms look like?
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ANSWER 3
They are long worms (up
to 25 meters in length),
consisting of flattened
segments (proglottids)which get progressively
smaller towards the head
end, or scolex The scolex
is attached to the mucosaof the small intestine
with suckers, and/or
hooks.
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QUESTION 4
Man is the definitive host for Taenia species (the beef
and pork tape worms). What does this mean?
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ANSWER 4
It means that adult tapeworms can only survive in the
gut of humans. The eggs are discharged from segments
passed in the stools, and these require an intermediate
host to complete the cycle. The intermediate hosts arecattle, in the case of T. Saginata, and the pig or other
animals (including the dog) in T. Sollum.
Continued...
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ANSWER 4 (Contd…)
Adult worms in gut
Eggs and segments
passed in stool
Child ingests eggs
Eggs ingested by pigLarvae form cysts in pig’s
muscles
Undercooked pork eaten
Cysts form in tissues
(Cysticercosis)
Life cycle of Taenia solium
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QUESTION 5
How then is the life cycle completed?
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ANSWER 5
Eggs are ingested by the animal (cow, pig or dog) and
the larvae migrate to form cysts (cysticerci) in the
muscles of the intermediate hosts. Man eats the flesh of
these hosts, (generally beef or pork) , and the cysticercimature into adult tapeworms in the gut.
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QUESTION 6
If a human ingests the eggs, what happens?
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ANSWER 6
In the case of the pork tapeworm, cysts can form in the
tissues in the same way, resulting in Cysticercosis. For
some reason, beef tapeworm larvae cannot migrate in
humans.
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QUESTION 7
What are the clinical features of tape worm infestation?
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ANSWER 7
In most cases the presence of the adult worm is quite
symptomless segments (proglottids) are merely passed
in the stools. There may be symptoms of allergy -
urticaria or pruritis ani, and a mild eosinophilia in the blood count. They do not feed on the mucosa of the gut
and simple absorb nutriment from the bowel contents.
Rarely worms can cause obstruction to the bowel, or a
segment migrate into the appendix to cause appendicitis.
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QUESTION 8
What then is the importance of tapeworm?
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ANSWER 8
Cysticercosis is an important health problem in
communities where pigs are allowed to run free, and
children pick up the eggs in food, water, dust or dirt,
thus developing the cystic form. They are also a danger to themselves by auto-infection that is, transfer of eggs
from hand to mouth.
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QUESTION 9
Where do the cysts develop?
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ANSWER 9
Cysts can develop almost
anywhere in the body -
beneath the skin, in
muscles and heart, in theeye, and, most
importantly, in the brain.
They do not cause
symptoms until they die,swell and calcify usually
some years after
infection .
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QUESTION 10
What are the symptoms of Cysticercosis?
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ANSWER 10
The severity increases with the number of cysts present.
The most important effects are caused by cysts in the
brain (neurocysticercosis). There are focal or
generalised seizures, sometimes with personalitychanges and other neurological effects.
Neurocysticercosis is a common cause of epilepsy in
some parts of the country rural areas where pork is
commonly eaten.
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QUESTION 11
Are there other symptoms of Cysticercosis?
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ANSWER 11
When present in the eye they can cause retinal
detachment and loss of vision. Cysts elsewhere are
usually benign.
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QUESTION 12
How is tapeworm diagnosed?
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ANSWER 12
The segments when
found in the stool are
typical. The proglottids
of T saginata and Tsolium have slightly
different appearances
which can be
distinguished under amicroscope.
Continued...
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ANSWER 12 (Contd…)
The eggs of tapeworm
are also very
characteristic, though the
2 species are identical inappearance.
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QUESTION 13
How is the diagnosis of Cysticercosis made?
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ANSWER 13
Usually with the
assistance of imaging
techniques. Calcified
cysts may be seen instraight X-rays of
muscles (as in this case)
or skull, but this is only
found in longstandingcases.
Continued...
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ANSWER 13 (Contd…)
Far more sensitive is the
use of the CT scanner,
particularly so in
neurocysticercosis. As inthis slide. It shows
numerous small cysts.
When cysts die there is
an inflammatoryresponse, hence the
oedema present round
some lesions.
Continued...
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ANSWER 13 (Contd…)
When in or near the
ventricles larger
multilocular cysts may
form, sometimes causingobstructive
hydrocephalus.
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QUESTION 14
Are there any other means of diagnosis?
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ANSWER 14
Serological tests are available, such as an ELISA test,
which can be used on blood or CSF.
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QUESTION 15
What is the treatment?
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ANSWER 15
The adult tapeworms - both T saginata and T solium -
can be rapidly eliminated with Praziquantel, as a single
oral dose of 10-20 mg/kg. Niclosamide (Yomesan) is
also effective (0,5 gm as a single tablet, repeated in onehour).
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QUESTION 16
How would you treat neurocysticercosis?
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ANSWER 16
There is now general agreement that killing the cysts all
at once is the best line of attack. This can be
accomplished with praziquantel in a dose of 50 mg/kg
per day in 3 divided doses for 14 days. Albendazole 15mg/kg per day for 5 days has also been shown to be
effective. The administration of corticosteroids controls
the brain swelling which can accompany death of the
cysts. Anticonvulsant may also be required.
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QUESTION 17
What other cestode parasites are of importance in
Southern African children?
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ANSWER 17
In terms of severity of
clinical effects, the most
important is the
tapeworm Echinococcusgranulosus. This is a
small worm which lives
in the intestine of the
dog.
Continued...
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ANSWER 17 (Contd…)
The dog is thus the definitive host. The eggs which are
passed in the dogs stools are eaten by sheep
(intermediate host) and the larvae develop into hydatid
cysts in the tissues.
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ANSWER 17 (Contd...)
The cycle is completed when dogs are fed sheep offal
containing the cysts. Children become infected when
they pick up eggs from the dog's fur or from the dog's
tongue after licking.
Continued...
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ANSWER 17 (Contd...)
Adult worm in
jejunum of dog
Eggs passed in stool
Child ingests eggs
Larvae
penetrate
bowel wall
Eggs ingested in sheep
Larvae form cysts insheep’s flesh
Dog eats sheep offal
Cysts form in tissues
(liver, lungs, bone, brain)
Life cycle of Echinococcus (Hydatid)
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QUESTION 17
Where do the cysts form?
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ANSWER 17
The most common sites
are the lungs and the liver,
but any tissue, including
bone, may be invaded.
When allowed to grow,the cysts become large
round swellings, and cause
symptoms like a tumour,
by pressing on organs.This may take years to
develop. The fluid from
cysts contain hydatid
'sand' and hooklets.
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QUESTION 18
Can there be any more severe symptoms?
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ANSWER 18
If fluid is allowed to leak out of the cyst, severe allergic
symptoms can result.
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QUESTION 19
How is the diagnosis made?
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ANSWER 19
Usually by arranging - straight X-ray, ultrasound of CT
scan - when the appearances are usually very
characteristic. A significant eosinophilia is generally
present. The most reliable serological test is the 11-RC-5 test.
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QUESTION 20
How is hydatid treated?
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ANSWER 20
By surgical removal whenever possible, special care
being t taken to avoid spilling the contents. In inoperable
cases, albendazole has been used in a dosage of 10
mg/kg a day for 8 weeks.
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QUESTION 21
Can hydatid disease be prevented?
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ANSWER 21
Yes. By:
– enforcing regulations against dogs eating sheep offal,
and
– by the regular de-worming of dogs in affected areaswith praziquantel every 2 months. Using these
measures hydatid disease has been totally eliminated
from some regions.
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QUESTION 22
Are there any other tapeworms of importance to us?
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ANSWER 22
Several other species are common in Southern Africa,
but they seldom cause significant symptoms, and so
will not be discussed further here. They are:
– Hymenolepis species – Dipyllidium caninum, and
– Inermicapsifer madagascariensis.
These worms are readily eliminated by praziquantel or
niclosamide.
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QUESTION 23
What are trematode worms and how do they differ from
the nematode and cestode worms?
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ANSWER 23
TREMATODES (FLUKES) are a family of worms
which have flattened bodies, have a gut, but no body
cavity, and a dorsal and ventral sucker. By far the
most important members of this family in SouthernAfrica are the Schistomes. They are so called because
the male has a fissure in the body in which he carries
the female (see next slide).
Continued...
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ANSWER 23 (Contd…)
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QUESTION 24
What are the most important schistosome worms in
Southern Africa?
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ANSWER 24
Schistosoma haematobium and S mansoni are
responsible for SCHISTOSOMIASIS, also known as
BILHARZIA. Bilharzia is widespread in Botswana,
Zambia, Zimbabwe and Mozambique, and in the NorthEastern parts of South Africa, as far South as the Port
Elizabeth area. Another schistosome, S matheii, lives in
cattle and game, and is thought to infect humans too,
perhaps by hybridising with S haematobium. A third
member of the genus of great importance is S
japonicum, but this is only found in the Far East.
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QUESTION 25
Describe the life cycle of S haematobium.
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ANSWER 25
This is complex, and requires man as the definitive host,
and certain species of fresh water snails as the
intermediate host.
Continued...
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ANSWER 25 (Contd…)
Eggs laid in
portal veinsEggs are passedin urine
Child
passesurine inwater
Larvae
(miracidia)hatch seek outsnail
Cyclecontinues
in snailLarvae
(cercariae)emerge,
seek out human
Worms mature in
portal veins
Cercariae penetrate
skin
Larvae(Schistosomulae)
circulate
Life cycle of S haematobium
Continued...
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ANSWER 25 (Contd…)
The adult worms live in the portal veins of the human,
the female lives continuously in amatory union, partially
enclosed in the male.
The female lays eggs in the plexus of veins around the bladder, and the eggs digest their way through the
bladder mucosa to be passed in the urine. The resultant
damage to the mucosa, bladder wall and ureters causes
the symptomatology of bilharzia.
Continued...
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ANSWER 25 (Contd…)
When the child urinates in rivers or dams eggs are
passed into the water. The tiny larva, or miracidium, is a
good swimmer and must find a snail, which it enters, to
complete the next phase of its cycle.
Continued...
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ANSWER 25 (Contd…)
Another free swimming
larva, the ceraria, leaves
the snail, and must find a
human within a fewhours or it is no longer
infective.
Continued...
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ANSWER 25 (Contd…)
The cercaria penetrates
the skin of the host,
sheds its tail, and then
enters the blood stream,eventually reaching the
portal veins, in which it
matures to adulthood The
worms can survive there
for many years.
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QUESTION 26
Is the life cycle of S mansoni any different?
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ANSWER 26
The worms prefer the veins of the bowel rather than the
bladder, and the passage of eggs causes damage to the
colon, mainly. Eggs are therefore passed in the stool and
not in the urine. The human defecates near water, andthe eggs, which can survive in the moist stool for some
time, are washed by rain into the water source. The rest
of the cycle is similar to S haematobium.
Continued...
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ANSWER 26 (Contd…)
Eggs
laidPass
through
bowel wall
Eggs in
stoolEggs
washed
into water
Larvae
(miracidia)hatch seek
out snail
Cycle continues in
snail. Larvae(cercariae) emerge
seek out human
Worms mature in
portal veins
Larvae
(Schistosomulae)
circulate
Cercariae
penetrate skin
Life cycle of S mansoni
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QUESTION 27
The clinical features of schistosomiasis may present in
4 stages. What are they?
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ANSWER 27
Clinical features of Bilharzia:
– Swimmers’ itch
– Katayama fever
– Early egg-laying stage
– Late egg-laying stage
– ? malignancy
Continued...
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ANSWER 27 (Contd…)
Symptoms may be associated with each of 4 stages of
the infection.
– At the time when the cercariae penetrate the skin an
itchy eruption may develop, lasting a few days'Swimmers' itch'. A similar rash may be caused by
other types of schistosome found in birds, in
countries where bilharzia is unknown.
Continued...
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ANSWER 27 (Contd…)
– The schistosome larvae (schistosomulae) enter the
lymphatic and thence to the blood stream, eventually
reaching the portal veins and the liver where they
mature into adult worms. This migratory phase may be associated with systemic symptoms due to release
of metabolic products of the schistosmes. This has
been called 'Katayama Syndrome'.
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QUESTION 28
What are the features of the ‘Katayama Syndrome’?
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ANSWER 28
Features of Katayama Syndrome. There may be any or
all of the following:
– Fever and malaise
– Cough – Marked eosinophlilia
– Liver tenderness, splenomegaly
– Abdominal discomfort and diarrhoea
– Joint and muscle pains
– Urticaria, sometimes anaphylactoid purpura
– Rarely, encephalopathy, myocarditis
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QUESTION 29
What are the other stages?
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ANSWER 29
The early egg-laying stage:
– Dysuria, frequency and terminal haematuria, in the
case of S haematobium infection,
– Symptoms of dysentery in S mansoni
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QUESTION 30
Do these symptoms always occur?
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ANSWER 30
No - the majority of infections pass unnoticed. But
bilharzia may be the cause of vague ill health and poor
performance at school. It is only in the heavier
infections, and in individuals with no prior immunity,that illness is apparent.
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QUESTION 31
How long does this process last?
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ANSWER 31
Initially the eggs pass rapidly across the mucosa, but
gradually there is more and more reaction of the body's
tissues to the eggs. Granulation tissue traps the eggs and
results in fibrosis and eventually calcification - the lateegg-laying stage. This may take years to develop, but is
not uncommonly seen in older children.
Continued...
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ANSWER 31 (Contd…)
Late egg-laying stage:
– chronic urinary obstruction
– bowel polyps and strictures
– liver fibrosis
– carcinoma of bladder, liver
Continued...
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ANSWER 31 (Contd…)
The earliest signs are
'sandy patches' in the
lower part of the bladder
- the trigone. Later theremay be calcification of
the bladder wall and
fibrosis of the ureters,
leading to obstruction in
the flow of urine -
hydronephrosis.
Continued...
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ANSWER 31 (Contd…)
Changes in the bowel are
usually more subtle, but
there can be stricture
formation and polyps inthe colon.
Continued...
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ANSWER 31 (Contd…)
Hepatic fibrosis leading to portal hypertension.
Eggs lodging in the lungs and nervous system
(especially the spinal cord) may result in chronic
cardiovascular and neurological syndromes. Schistosomiasis has been incriminated as a risk factor
in carcinoma of both the bladder and liver.
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QUESTION 32
How would you diagnose schistosomiasis?
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ANSWER 32
By finding the typical eggs in urine or stool. To confirm
that the disease is active the eggs must be shown to a
alive (viable) by seeing the typical movements within
the egg. For this reason a fresh preparation of stool or urine must be available (not a stained slide).
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QUESTION 33
What species is the
ovum in this slide?
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ANSWER 33
S haematobium, because of the spine at the end. The
ovum of S mansoni has a spine on its side.
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QUESTION 34
What is the treatment for schistosomiasis?
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ANSWER 34
Praziquantel is the treatment of choice for all forms.
And is on the WHO 'essential drug list'. It is both safe
and highly effective, in a single dose of 40 mg/kg.
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QUESTION 35
Who should receive treatment?
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ANSWER 35
This is a more complex problem. In some areas virtually
all members of a village will be affected. The children
are the heavy passers of eggs, as resistance gradually
builds up in adult life. Since a safe, effective treatment
is available, mass treatment of the whole population is
now possible, but there are clearly financial constraints
to this policy. Treatment can be limited to specific
groups, for example:
– certain age groups, or
– those with heaviest haematuria or egg load
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QUESTION 36
What other measures are there to prevent bilharzia?
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ANSWER 36
Preventing snails from becoming infected by:
– limiting human access to water in highly infected
areas, by building protected canals, etc
– providing latrines and discouraging urination in, anddefecation near natural water
Snail control by:
– eradicating vegetation favouring snail growth
biological methods, e.g. snail-eating fish
Continued...
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ANSWER 36 (Contd…)
– special attention to prevent snail breeding in new
irrigation schemes
– snail control by chemical killing has become less
popular because of harmful effects on theenvironment
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QUESTION 37
Are there any other trematode worms of importance to
children?
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ANSWER 37
There are a number of flukes which can infect the liver,
intestine and lung, but none are common in Southern
Africa.
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FURTHER READING
GOLDSMID, KIBEL AND MILLS; Helminth
infections. In Forfar and Arneil's Textbook of
Paediatrics; 5th edition 1998 pages 1481-1513
COOVADIA & LOENING; Paediatrics & Child Health;1992; p212 - 217
JEFFREY; Atlas of Medical Helminthology &
Prctozoology; 1991; p5
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THE END