Helminthes
The helminthes or worms unlike the protozoa are macroscopic and
multicellular ,they have digestive ,excretory, reproductive and
nervous systems, through these may be lacking or highly modified in
some species .like the protozoa the worms can be categorized
according to their habitat in the host ,there are intestinal round
worms ,liver ,flukes, blood parasite as well as many free living species
.helminthes have an outer protective covering "cuticle" the month
may be provided with teeth or cutting plates …many helminthes
possess suckers or hook for attachment to host tissues they don't
possess organ locomotion ,but in some species the suckers assist in
movement (locomotion is generally by muscular contraction and
relaxation .
 Helminthes do not possess body cavity.
 have a primitive nervous system
 The excretory system is better developed
 The greatest development is seen the reproductive system may be
1-diecious (with two distinct male and female sexes) separate ,the
male being smaller than the female)
2-Hermaphroditic helminthes ,both male and female reproductive
system are present in the same worm and self- fertilization
 The eggs or larvae are produced in enormous numbers
 Survival and development are further complicated by the fact
 Many helminthes require more than one intermediate host for
completion of their life cycle.
Classification
Based on their shape and other characteristics helminthes are
classified into two broad groups
1- The cylindrical worm belonging to the phylum
nematheliminthes(class nematode) name-thread .
2- Flat worms belonging to the phylum platy –helminthes-platys –
flat.
 The flat worms in turn are classified into two categories –the
leaf-like( class treamatoda )and tape-like (class cestoda) or
tape worms
Nematodes
Are elongated cylindrical worms with an segmented body .they
possess relatively well developed alimentary canal ,complete with the
anus,the head does not have either suckers or hooks, but may have a
buccal capsule with teeth or cutting plates "the sexes are separate"
Trematodes
Have flat or leaf-like unsegmented bodies the alimentary canal is
present ,but in complete ,without anus , they posses suckers but no
hooks the sexes are separate in schistosomes ,while the other flukes
are hermaphroditic .
Cestodes
Have tape-like segmented bodies ,they do not possess an alimentary
system .the head carries suckers and some also have hooks, they are
mosnoecious .
Trematodes :fluke
Trematodes are unsegmented helminthes which are flat and broad.
resembling the leaf of a tree ,they vary in size from the species just visible to
the naked eye, like heterophyes to the large fleshy flukes like fasciala and
fasciolopsis . Medically important members of the class treatment belong to
the subclass diagenea ,
diagentic (require two hosts)
- The definitive hosts in which they pass the sexual or adult stage are
mammals (ex. amen)
- Intermediate hosts in which they pass their asexual or larval stage are
fresh mollusks ,snails.
Flukes are hermaphroditic (monoecious) except for schistosomes in which
the sex are separate .
- Presence of two muscular cup-shaped suckers the oral sucker
surrounding the mouth at the anterior end and the ventral sucker in
the middle ventrally
- They have no body cavity & circulatory or respiratory organs .
- The alimentary system consists of month surrounded by the oral
suckers ,a muscular pharynx and the esophagus which bifurcates
anterior to the ventral sucker to form two blind caeca …..(which
reunite schistosomes) the anus absent .
- The reproductive system is well developed ,the hermaphroditic flukes
have both male and female structure so that self –fertilization take
place .in the shistosomes the sexes are separate but the male and
female live in close apposition (in copula) .
-
Immature stages of flukes:
1- The egg : operculated or spined it is agrem cell or miraciduim
enclosed in a shell
2- The miracidium: a ciliated larva which may be free –swimming or
may hatch inside a shell .
3- Sporocyt :intromolluscan ,non ciliated suc-like containing germ
balls .
4- Redia :intra molluscan and develops from the gram balls of the
sporocyst ; from it the cercaria emerges .
5- Metacercaria . encysted cercaria ,with out a tail ,but with resisent
cyst wall .it is usually formed on plants fish or other animals .
Trematodes infecting man can be classified as follows .
a- Diecious blood flukes or schistosomes which live inside veins in
various location
1- In the vesicle and pelvic venous plexuses ,schistosoma
haematobium .
2- In the inferior mesenteric vein--- s.mansoni
3- In the supeeior mesentricvein ----s.japanicum
b- Hermaphroditic flukes which live in the lumen of various
tracts1-biliary tract (liver flukes ---- fasciola hepatica ,
clonochis sinensis , opisthrochis sp.)
2- gastrointestinal tract (intestinal flukes)
a- Small intestine
fasicolopis , heterophyes heterophyes ,
metagonimmus yokogawai .
b- Large intestine
Gastrodiscoides homins
4- Respitary tract (lung fluke)
Parayonimus westermani
** blood flukes: schistosomes:
Human schimstosomiasis (bilharzias ) schistosomes are
diecious treatment in which the sexes are separate the male is broader
than female,and its lateral borders are rolled ventrally into cylindrical
shape ,producing a long groove called gynaecophoric canal, in which the
female is held. all schistosomes live in venous plexuses in the body of
the definitive host.The location varying with the species .
Schistosomes Differ from the Hermaphroditic trematodes in many Respects
 They lack a muscular pharynx
 Their intestinal caeca reunite after bifurcation to from a
single canal
 They produce non- operulate eggs
 They have no redial stage in larval development
 The cercariae have forked tails and infected by penetrating
the unbroken skin of definitive hosts
Schistosomiasis (bilharzias is) is a water –borne disease constituting animportant public health problem
Morphology
The male is covered by finely tuberculated cuticle ,it has two muscular
suckers and prominent .The oral sucker being small and the ventral
sucker large and prominent. beginning immediately behind the ventral
sucker and extending to the caudal and is the gynoecophric canal in
which the female worm is held. The adult female with the cuticular
tubercles confined to the two Eds.
life cycle: It is basically similar in the all species .
Eggs of haemotobium pass with urine which of mansoni pass with faeces
.in water egg hatches giving miracidium which seeks about the
intermediate host which is a snail
 Bulinus
for Haematobium
 Biomphalaria
for mansoni
 Inside the snail miracidium develops into
sporocyts then
to cercaria ( radial stage absent) cercaria seeks about body of
man and is attracted to it by its warmth after losing its tail it
finds its way into a capillary to reach the systemic circulation
and finds its way into a capillary to reach the systemic
circulation and finally the liver and portal circulation after
maturation in the liver and hepatic branches of the portal
veins, haematobium select the venous plexuses of urinary
tract, while mansoni migrates to branches of the inferior
mesenteric veins related to the colon due to states within the
venules ,piercing action of spine and the lytic action of an
enzyme secreted by the miracidium inside the ova the eggs
breaks through the wall of vessels and escape into the lumen
of the bladder (haematobium ) or the colon (mansoni )
together with blood .
Pathogenicity and clinical features
1- The invasion stage extending from the period of exposure to
cercariae till formation of adult and beginning of egg laying
generalized and localized reaction occurs due to metabolites of
growing and mature worms
2- The stage of egg deposition and extrusion. the period between egg
deposition and their appearances in the urine or faces.. trauma and
hemorrhage as eggs pass from the venules are the main pathogenic
feature
3- The stages of tissue proliferation and repair… it is a late stages
initiated after egg deposition in tissue and their extrusion is
progressing .the present of eggs in tissue ---- tissue reaction
producing formation of local tubercles or granulomatus lesion with
deposition of histocytes ,plasma cells and fibroblastic proliferation
and development of scar tissue which may lead to strictures
chronic ulcers and other pathological changes
Diagnosis:
1- Direct …A. The most important diagnosis method to find living eggs :

Urine for s.hamatobium ,eggs with characteristic
terminal spines can be demonstrated by microscopic
examination
Specimens collected between midday and 2 pm are most likely to
contain eggs
sedimentation
 Filtration
 Stool for mansoni ,lateral spin
 Best
egg. concentration technique
formal - ether TIF (Thiomersal, iodine formal)
glycerol sedimentation.
 B-rectal biopsy for all schistosomes asmall pieces of rectal
mucosa is removed by biopsy forceps .it is placed on slide
under a cover slip and examined with x10 power
 S.hamemotobium eggs are often trapped in the rectal
mucosa.
 S.mansoni
more often look
2- Indirect method
 As intradermal test(Fairley's test)
 Compliment fixation test
 EliSA
Although the better ones correlate well with the results of direct
diagnostic methods.
Treatment
 Metriphonate is the drug of choice in schistosomiasis to
haematobum
 Prazignatel is effective against all schistosomes prevention
and control
 Eradication of the intermediate hosts (copper sulphate 10
p.pm)
 Prevention of environmental pollution with urine and faces
 Effective treatment of infected persons .
Fasciola
Fasciloa hepatica: the sheep liver fluke cause disease primarily in
sheep and other domestic animals… humans are infected by eating
watercress ( aquatic plants) contaminated by larvae (metacecariae )
that excyst in the duodenum ,penetrate the gut wall and reach the liver
where the mature into adults .hermaphroditic adult in the bile ducts
produce eggs which are excreted in the feces .the eggs hatch in fresh
water and miracidia enter the snails .miracidia develop into cercariae,
which then encyst on aguatic vegetation….sheep and humans eat the
plants thus completing the life cycle.
Symptoms :are due primarily to the presence of the adult
Worm in the biliary tract in early infection ,right –upper guardant pain, fever
and heapatomegaly can occur ,but most infections are asymptomatic
 Months or years later obstructive jaundice can occur.
Pathogenesis:
In invasion stage symptoms are caused by penetration of the intestinal
wall,migration across the peritoneal cavity and entry into the liver.
 Small nectotic foci and micro-abscess have been describe .
 f.hepatica is large and so causes more mechanical damages
so it causes parenchymal injury.
 Patients present initially with fever
 Eosinophilia and tender hepatomegaly. later they develop
acute epigastric pain, obstructive jaundice and anemia.
 Halzoun (meaning suffocation) and is a painful pharyngitis
caused by the presence of adult flukes on the posterior
pharyngeal wall phyaryngeal wall. the adult flukes are
acquired by eating raw sheep liver
Diagnosis :
is made by identification of eggs in the feces. eosinophilia is constanly
present
Treatment by praziguantel and bithonal are effective drugs… oral bithionol
- Intramuscular emetine has been used successfully
 adult flukes in the pharynx and larynx can be removed
surgically… prevention involves not eating wild aguntic
vegetables or raw sheep liver.
Halzoun : is particularly common in Lebanon and other parts of the middle
east and north Africa
Diagnosis: demonstration of eggs infaeces or aspirated bile is the best
method of diagnosis . Diagnosis is made by identifying the large
ovale,golden brown operculated eggs in the feces of an infected animal
.the identification can be made by sedimentalue techniges .
The fluk eggs will often not be present in the feces during acut stages of
disease .
Others oriental liver flukes
 Opisthorchis spp:
Clonorchis sinensis
Opisthorchis felinens , opisthorchis viverrini
Lung flukes
Paragonimus westermani :