Round worm pdf - د. محمد العاني

Phylum Nematoda

(Round worm)

General charecterstics

trichiura

Trichurs

Describe

Morphology ,life cycle, pathogenesis ,

clinical presentation

Lab. diagnosis

vermicularis

Enterobius

Morphology ,life cycle, pathogenesis ,

clinical presentation Lab. diagnosis

Learning objective

Phylum Nematoda

(Round worm)

The most abundant animals on the earth

Either free living or parasite of animals & plants

They are bilaterally symmetrical ,
unsegmented, elongated , tapering at
both ends & posses a pseudocoel (body
cavity) {

not lined with peritoneum or

mesothelium

}

The body is covered with a non cellular

cuticle

which is secreted by the underlying

hypodermis

The sex is separated ( bisexual the )

female

is longer than the male & most of them are
oviparous

while the male is shorter & has a

more curled tail

Size vary from less than one mm to several
centimeters

Body wall consist of

outer cutical , inner muscular

& intermediate hypodermis

The surface coat is important in evasion

of the immune response

Pseudocoel

;

The body wall enclose a fluid filled (

Hemolymph

)

cavity the pseudocoel which differs from a true

coelom in that it has no peritoneal lining

Its function as hydrostatic skeleton , the
alternation of contraction & relaxation in
dorsal & ventral muscle impels the body
into series of curves producing S shape
motion seen in nematode locomotion

Thinner & longer««»»Shorter & thicker

Hemolymph important for transport of
solute & nutrient from one tissue to
another

Digestive system is complete with mouth,
gut & anus

The anterior part consisting of mouth,
buccal cavity & esophagus, all lined
with cuticula

mouth

is a usually circular opening

surrounded by lips (may be fused or absent)

Buccal

cavity lies between mouth&

esophagus which may be supported by
teeth as hook worms

Esophagus

is a muscular & cylindrical

region of the digestive tract which sucks
food & forced it into the intestine ,the
esophagus often has one or more
enlargements called

bulb

Mid-gut)

)

Intestine ;

tube like structure extends from eso.-rectum

The wall of the intestine consist of simple
columnar cells with microvilli for nutrients
absorption

( the food is either blood,

tissue cells ,fluids ,intestinal contents or
combination of them)

also the

intestine serves as a primary means of
excretion of nitrogenous waste products

Rectum

(hind-gut)

Which is lined with cuticula & ends
in anus

in male receives the products of
reproductive system into its terminal
portion so it is a

cloaca

which

contain the copulatory specules

Nervous system

;

Is very simple, two main concentrations of
nerve elements ,one in

esophageal region

,the other in the

anal region

,connected by

longitudinal nerve trunks.

The main sense organs are,

cephalic &

caudal papillae

( the later aids in copulation)

Predominant neurotransmitter is

acetyl choline

Several of nematocidal drugs interfere with

neural functions

as piperazine or mebandazole paralyzing the
worms →passing out of the host

Male are smaller than Female

Male with coiled tail ,often associated with
external feature as bursae, copulatory

spicules & papillae

Female reproductive system either
single set as in Trichuris

or (mostly) paired, consist of ovary,
oviduct, uterus, vagina

& vulva which is ventral in

position

The daily production of eggs per female varies

greatly in different species ,also the stage of
development at the time of oviposition also
varies;

Eggs of Ascaris & Trichuris are

unembryonated

Those of Hookworms are in early

stages 4-8 cell

Those of

Strongyloides

are in

morula

& larva

leaves the host

Trichinella & filariae eggs develop completely &
hatch in uterus(

larviparous

)

The fundamental stages in nematode life
cycle are the

egg

four larval stages

, &

the

adult

In the majority of intestinal nematodes
intermediate host is not present so there
is a necessary period of development
outside the body ,frequently in

soil for

complete larval development

The Intestinal Nematodes found either

free in the intestinal lumen as Ascaris

attached to the wall of intestine as

Hookworm

embedded deeply in the intestinal

mucosa as strongyloides

Nematodes

With Larva

migration

Without larva
migration

trichiura

Trichurs

vermicularis

Enterobius

Large intestinal nematodes (cecum &iliocecal junction)

293

Trichurs trichiura (Whip worm)

long

Trichurs trichiura

anterior thread or whip like structure which

Is imbedded in the intestinal mucosa

Posterior portion is fleshy & board which is free

in the intestinal lumen

Mouth lacking lips

Male is smaller with single spicule

Anterior end
3/5 from the
body, thread
like for both

sexes

Posterior end
2/5 from the
body, wider and
fleshed for both

sexes

The posterior in
the female like a

comma or arc

The posterior of male caudal
extremity is coiled ventrally,

contain sheathed spicule

– 4 cm

– 5 cm

Fig 248 : Trichuris trichura male and female

Note : adult worm white or pinkish in colour

302

Each female produce 3000-20000 egg/day

Ova is a barrel shape with a prominent opercular

Plug at each end ,

unemberyonated

when passes with stool

Emberyonation is complete in about 21 days in

Soil which must be moist & shady

Fig 249 : Trichuris trichiura Egg 50 X 25 µm

Note : the egg barrel

– shaped, with two polar plugs yellowish brown in colour

( bile

– stained ) has a double shell, the outer one is

bile

– stained

In Iodine s.

In saline s.

Plug

303

When swallowed hatch & the larva enter crypts
of Lieberkuhn of large intestine

Worms begin to grow & tunnel within the
epithelium & break towards the luminal surface

Then the enlarging posterior portion breaks of
the epithelium & protrudes into intestinal lumen
all this requires 3 months

Anterior end remains embedded in the gut
mucosa ,so it is a tissue parasite & lives there
for several years

Trichuris trichiura

Life cycle

Fig 247 : life cycle of

Trichuris trichiura

301

Fig 251 : Trichuris trichiura Adult Appendix Section

305

Hematoxylim - eosin s.

Epidemiology Trichurs trichiura

requires

poor standard of sanitation

which human feces are deposited on the soil

Associated

with worm climate high rainfall

Humidity (shady area)

Prevalence 1-2%especially small children

infection

The infective stage is mature ova from

contaminated soil

Geophagy eating soil ,usage of feces as fertilizer

House fly as mechanical vectors

Pathology

Fewer than 100 worms rarely causes

Clinical symptoms (majority are symptom less)

Symptom of trichuriasis

→

>200

Small children are particularly prone to heavy

infection

Dysentery,

anemia

, growth retardation , finger

clubbing

(systemic nature of the effect of infection)

rectal prolapse

→→

Frequent location in cecum & appendix

Appendicitis

Fig 250 : symptom, with heavy infection ( prolapse of the rectum )

304

The anterior end buried in the mucosa so the
worm feeds on cell contents & blood

The inflammatory response leads to increase
macrophages in the colonic lamina properia
& increase level of TNF in mucosa & blood
also increases in IgE

Diagnosis; Demonstration of eggs & worms in
stool

Treatment; mebendazole, albendazole--------

Small children are particularly prone to heavy

Infection with Trichuriasis they may have all the followings
except

A-Dysentery& anemia

b-finger clubbing

(systemic nature of the effect of infection)

rectal prolapse

D-Ulcerative colitis

Ova of T. trichura is a barrel shape with
a-aprominent opercular Plug at each end

B-unemberyonated

when passes with stool

Emberyonation is complete in about 21 days in

C-Soil

D-Have polar thickening & polar filaments

vermicularis

Enterobius

Enterobius vermicularis (pin worm)

Most common nematode of man

Female is slender with sharp , pointed

Tail (8-12 mm)

Male posterior end curved ventrally with

Single spicule(2-4 mm)

Have 3 lips surrounding the mouth,

Followed by cuticular inflation of the head

Cuticular expansion

Fig 241 : Enterobius vermicularis Adult Anterior end

Note : the cuticular cervical expansions ( alae ) and the double

– bulb muscular

oesophagus ( similar in both sexes )

Cervical alae

Oesophagus

Bulb

Globular bulb

295

Fig 242 : Enterobius vermicularis Adult Male 2

– 4 mm X 0.1 – 0.2 mm

posterior end is curved with one spicule, rarely seen in stool

296

Fig 243 : Enterobius vermicularis Adult Female ( 8

– 12 mm X 0.3 – 0.5 mm )

Note : white in colour, spindle shaped and resembles a short piece of thread, pointed

tail macroscopically seen in stool

Enterobius vermicularis Adult

Female Posterior End

297

Female when gravid the 2 uteri contain

Thousands of eggs

Egg is enlongated oval & flattened on one

side

( D shape)

Fig 244: Enterobius vermicularis Egg 50

– 60 X 30 µm

Note : colourless D

– shape ( flattened on one side and convex on the other, thick

double

– walled shell )

rarely seen in stool smear

In Iodine s.

298

Adult worm habited mainly iliocecal region

Although the worm can wonder through out

The GIT from the stomach to the anus

They attached themselves to the mucosa

Where they presumably feed on epithelial cells
& bacteria

The gravid female begins migrating within the
lumen of intestine , passing out of the anus on
to perianal skin where they crawl about on the
outer skin , where they leave their eggs.

One worm may deposits about 5000—15000
eggs , female soon die after oviposition

While the male die soon after copulation

So in intestine female > male

Ova when laid it contains a partially developed
larva which will be developed to infectivity

within 6 hr. at body temperature

re-infection or auto-infection

is very

common

Auto-infection can occur by two routs

Egg swallowed then hatched in the duodenum ,
the larva slowly move down in the intestine ,
molting twice to become adult by the time
they arrived to the iliocecol junction ,the total
time from ingestion →sexually mature worm
about 15-45 days

Or if the perianal folds are uncleaned for a long
period , the attached ova hatches and the
released larva wonders into the anus & hence
to the

intestine

(retro-infection)

Epidemiology

Ova remain viable for weeks

Ova are very light so air born Clothing ,
towels & bedding rapidly become
seeded with eggs even the carpets

Most common means of infection is
through insertion of fingers & objects in
the mouth

Human can inhale then swallow the air
borne ova

Enterobius vermicularis

Life Cycle

: life cycle of

Enterobius vermicularis ( Oxyuris vermicularis )

294

Pathogenesis;

It has 2 aspects

1-damage caused by worms within the intestine,
because of the attachment to the mucosa
results in mild inflammation with or without
secondary bacterial infection

2-damage resulting from movement of female
out the anus &eggs deposition around the
anus leads to tickling sensation& scraching of
perianal area

Clinical features;

One third of infections are asymptomatic

Tickling sensation , pruritis &scratching of
perianal region leading to viscous circular
bleeding & bacterial infection

Patient feelings of nervousness, discomfort ,
restlessness, irritability, loss of appetite ,
nausea , vomiting, perianal pain, insomnia,
bed wetting & nightmare

Sometimes the worms wonders into appendix,
vulva , vagina ,uterus or peritoneum
→inflammation

: Enterobius vermicularis Adult in Appendix Section

Note : cuticular lateral alae like spine in cross section of adult worm

Lateral alae or

Lateral crest

Section of
adult worm

300

Hematoxylim - eosin s.

Diagnosis

By finding ova or adult worm

General stool exam is not helpful very few are
passing in stool

Sometime during night or early morning can see
the worm in the perianal area

Scotch (Cellophane) tape technique is
the method of choice for diagnosis

Scotch tape is held against a flat wooden
applicator with the sticky side out , pressed to
anal canal

At morning the tape is reversed & stuck on
microscopic slide

Sometimes egg recovered from under the nail or
swabbing the perianal region

The NIH swab. The

cellophane is now usually

replaced with sticky tape

Scotch tape technique ( graham swab )

: The techniques which used for detected the eggs of E. vermicularis from perianal
skin, eggs are rarely recovered in stool

Note :

eggs can also be recovered from under the finger nails

299

Treatment;

Mebendazole (vermox) repeated after 7-10
days

All family must be treated

All bed lines & towels washed in hot water &
the home must be cleaned