common intertinal worms found in southern africa

7/28/2019 Common Intertinal Worms Found in Southern Africa

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COMMON INTESTINAL WORMS

FOUND IN SOUTHERN AFRICA -

CESTODES AND TREMATODES

Prof. M A Kibeland

D Hanslo

QUESTION 1

How do cestode worms differ from the roundworms?

ANSWER 1

As a group they are:

– flat worms

– hermaphrodites (both sexes in same worm)

– have no body cavity

QUESTION 2

Which species of cestode are important clinically in

Southern Africa?

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.

QUESTION 3

What do tapeworms look like?

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.

QUESTION 4

Man is the definitive host for Taenia species (the beef

and pork tape worms). What does this mean?

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...

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

QUESTION 5

How then is the life cycle completed?

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.

QUESTION 6

If a human ingests the eggs, what happens?

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.

QUESTION 7

What are the clinical features of tape worm infestation?

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.

QUESTION 8

What then is the importance of tapeworm?

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.

QUESTION 9

Where do the cysts develop?

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 .

QUESTION 10

What are the symptoms of Cysticercosis?

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.

QUESTION 11

Are there other symptoms of Cysticercosis?

ANSWER 11

When present in the eye they can cause retinal

detachment and loss of vision. Cysts elsewhere are

usually benign.

QUESTION 12

How is tapeworm diagnosed?

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...

ANSWER 12 (Contd…)

The eggs of tapeworm

are also very

characteristic, though the

2 species are identical inappearance.

QUESTION 13

How is the diagnosis of Cysticercosis made?

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...

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...

When in or near the

ventricles larger

multilocular cysts may

form, sometimes causingobstructive

hydrocephalus.

QUESTION 14

Are there any other means of diagnosis?

ANSWER 14

Serological tests are available, such as an ELISA test,

which can be used on blood or CSF.

QUESTION 15

What is the treatment?

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).

QUESTION 16

How would you treat neurocysticercosis?

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.

QUESTION 17

What other cestode parasites are of importance in

Southern African children?

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

Continued...

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.

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...

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)

QUESTION 17

Where do the cysts form?

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.

QUESTION 18

Can there be any more severe symptoms?

ANSWER 18

If fluid is allowed to leak out of the cyst, severe allergic

symptoms can result.

QUESTION 19

How is the diagnosis made?

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.

QUESTION 20

How is hydatid treated?

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.

QUESTION 21

Can hydatid disease be prevented?

ANSWER 21

Yes. By:

– enforcing regulations against dogs eating sheep offal,

– 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.

QUESTION 22

Are there any other tapeworms of importance to us?

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.

QUESTION 23

What are trematode worms and how do they differ from

the nematode and cestode worms?

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...

QUESTION 24

What are the most important schistosome worms in

Southern Africa?

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.

QUESTION 25

Describe the life cycle of S haematobium.

ANSWER 25

This is complex, and requires man as the definitive host,

and certain species of fresh water snails as the

intermediate host.

Continued...

Eggs laid in

portal veinsEggs are passedin urine

passesurine inwater

Larvae

(miracidia)hatch seek outsnail

Cyclecontinues

in snailLarvae

(cercariae)emerge,

seek out human

Worms mature in

portal veins

Cercariae penetrate

Larvae(Schistosomulae)

circulate

Life cycle of S haematobium

Continued...

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...

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...

Another free swimming

larva, the ceraria, leaves

the snail, and must find a

human within a fewhours or it is no longer

infective.

Continued...

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.

QUESTION 26

Is the life cycle of S mansoni any different?

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...

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

QUESTION 27

The clinical features of schistosomiasis may present in

4 stages. What are they?

ANSWER 27

Clinical features of Bilharzia:

– Swimmers’ itch

– Katayama fever

– Early egg-laying stage

– Late egg-laying stage

– ? malignancy

Continued...

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...

– 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'.

QUESTION 28

What are the features of the ‘Katayama Syndrome’?

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

QUESTION 29

What are the other stages?

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

QUESTION 30

Do these symptoms always occur?

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.

QUESTION 31

How long does this process last?

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...

Late egg-laying stage:

– chronic urinary obstruction

– bowel polyps and strictures

– liver fibrosis

– carcinoma of bladder, liver

Continued...

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...

Changes in the bowel are

usually more subtle, but

there can be stricture

formation and polyps inthe colon.

Continued...

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.

QUESTION 32

How would you diagnose schistosomiasis?

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).

QUESTION 33

What species is the

ovum in this slide?

ANSWER 33

S haematobium, because of the spine at the end. The

ovum of S mansoni has a spine on its side.

QUESTION 34

What is the treatment for schistosomiasis?

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.

QUESTION 35

Who should receive treatment?

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

QUESTION 36

What other measures are there to prevent bilharzia?

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...

– 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

QUESTION 37

Are there any other trematode worms of importance to

children?

ANSWER 37

There are a number of flukes which can infect the liver,

intestine and lung, but none are common in Southern

Africa.

common intertinal worms found in southern africa

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