4. Morphology
Adult A. duodenale:
o Are grayish white or pink.
o Freshly passed worms are reddish in colour due to presence of
ingested blood in its intestine.
o Anterior end is slightly bent in relation to the body for which it
looks like a hook and hence it is named hook worm.
o They possess well developed mouths with two pairs of teeth.
o Male are shorter, the females are often longer and stouter.
o Males can be distinguished from females based on the presence
of a prominent posterior copulatory bursa.
4
5. o Oral aperture is not terminal but directed dorsally.
o Buccal capsule contains 3 pairs of teeth, 4 hooks and 2 knob like
plates on the dorsal surface.
o There are 5 glands connected
to the digestive system, one of
them called esophageal glans,
secrets a liquid which prevents
clotting of blood.
5
6. Mode of transmission
o Infective stage is filariform larva.
o Enters into the human body by penetrating the skin when a
bare-footed person walks on the faecally contaminated soil.
o The common sites of skin penetration are –
The thin skin between the toes.
The dorsum of the feet.
The inner side of the soles
Among gardeners and miners hands are the route of entry.
6
8. Segmented ova with 4 blastomeres passes through stool in the soil
Rabditiform larva develops inside the egg which subsequently
forms filariform larva (1st and 2nd moulting)
Filariform larva enters into the body by piercing the skin of feet
and hands and reaches to the blood stream
Larva passes through right heart to the pulmonary vessels where it
penetrates the vessel wall to enter into alveolar space
Larva climbs through trachea, larynx to crawl over the epiglottis
which is then swallowed
Swallowed larva passes through esophagus to settle down in the
small intestine (3rd moulting)
8
9. Larva in the small intestine develops into adolescent worm
(4th moulting)
At 3rd-4th week the larva becomes mature and fertilized females
begin to lay eggs in the faeces
The unsegmented eggs pas through faeces of the infected person
The eggs develop in the soil again and the cycle is repeated again
9
12. Pathogenic effects
Pathogenic effects are caused by –
o Those produced by larval forms in the skin:
At the site of entry through the skin.
During migration of larva through the lungs.
o Those produced by adult worms in the intestine.
12
13. o Pathogenic effects caused by larva of A. duodenale in the skin
Lesions in the skin
• Ancylostome dermatitis or ground itching: Common in
Necator infection than Ancylostoma and disappears within 1
or 2 weeks.
• Creeping eruption: Is a reddish, itchy papuler skin lesion
produced by aimless movement of the filariform larva in the
subcutaneous tissue for several month or years (up to 2
years). This larva is called “Larva migrans” which is common
in A. braziliense and A. caninum which can not penetrate
stratum germinativum and thus can not reach the blood
vessel.
13
15. Lesions in lungs
Bronchitis and broncho-pneumonia may occur along with
high eosinophilia when larva penetrates pulmonary vessel wall to
enter into the alveolar space.
o Pathogenic effects caused by adult worm are
Microcytic hypochromic anaemia due to –
• Chronic blood loss: Resulting from
* Sucking of .03-.2 ml blood/day/worm.
* Chronic blood loss from multiple biting sites.
* Pressure effect of the biting sites.
15
16. Nutritional deficiency due to –
• Iron deficiency
• Folate deficiency
• Vitamin B12 deficiency
• Iron + folate / B12 deficiency
16
17. Lab diagnosis
Sample: Stool
A) Direct methods –
1. Examination of stool
o Macroscopic examination of stool is necessary to find the
adult worms which may be passed out spontaneously.
o Microscopic examination of stool may easily demonstrate the
presence characteristic hookworm eggs.
17
18. Microscopic examination of stool:
Normal saline preparation Iodine preparation
Characteristics of eggs
∆ Oval or elliptical in shape floats in saturated solution of NaCl.
∆ Colourless not bile stained.
∆ Surrounded by transparent shell membrane.
∆ Contains a segmented ovum usually with 4 blastomeres.
∆ Wide clear zone between ovum and egg shell. 18
20. B. Indirect method
1. Examinations of blood
o PBF shows features of microcytic hypochromic anaemia.
o Eosinophilia
2. OBT is positive.
20
21. Treatment of hook worm
Treatment of hook worm infection consists of:
• Expulsion of worm by anthelmintic: Thiabendazole (25 mg/kg
for 2 days), Pyrental pamoate (10 mg/kg for 3 days maximum 1
gm), Mebendazole (100 mg twice for 3 days or 500 mg once) and
Albendazole (400 mg once).
• Treatment of anaemia: Specific anthelmintic should not be
started if haemoglobin is below 30%. In such case, anaemia should
be treated first and specific anthelmintics is to be started when
hemoglobin is above 50%. Ferrous sulphate (200-400 mg 3 times
daily) is given along with vit. B12 and folic acid.
21
22. Prophyaxis
1. Proper an complete treatment of carriers and diseased persons.
2. Prevention of soil contamination by proper sewerage disposal,
disinfection of stool and soil.
3. Wearing of boots and gloves.
22
23. Necator americanus
• Common in Sri Lanka, Australia and India but 1st discovered in
America.
Ancylostoma braziliense
• A parasite of dogs and cats in Brazil, India and Malaysia.
• Man is the accidental host.
• Can not penetrate the human skin and so, wander in
subcutaneous tissue causing skin eruption.
23
24. Differentiating feature of the two species (Adult worm)
A. duodenale N. americanus
Size Large and thicker Smaller and slender
Anterior end Bends in the same direction as
the body curvature
Bands in the opposite
direction to the body
curvature
Buccal
capsule
Contains 6 teeth, 4 hooks on
ventral surface and 2 knob-like
on the dorsal surface.
Pair of cutting plates
Copulatory
bursa
Dorsal ray is single Dorsal ray is split from the
base
Life span 1-5 yrs 18 yrs
24
