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The hookworms cause hookworm disease, which is one of the five major parasitic disease in China(malaria, shistosomiasis, filariasis, kala- azar and hookworm disease). At least two species of hookworms infect man, Necator americanus(美洲板口线虫)and Ancylostoma duodenale(十二指肠钩口线虫). They live in small intestine.

i morphology
I.   Morphology

1. Adults: They look like an odd piece thread and are about 1cm. They are white or light pinkish when living. ♀is slightly larger than♂.The male’s posterior end is expanded to form a copulatory bursa.

2. Eggs: 60×40 µm in size, oval in shape, shell is thin and colorless. Content is 2-8cells.


Differences between two hookworms

Adults of A. duodenale

Adults of N. americanus

Scanning electron micrograph of the mouth capsule of Ancylostoma duodenale, Note the presence of four "teeth," two on each side.
Scanning electron micrograph of the mouth capsule of Necator americanus, another species of human hookworm.  Note the presence of two cutting "teeth“.

Left picture: Copulatory bursa and spines of N. americanus(a side view);

  • Right picture: copulatory bursa of A. duodenale(a top view)
The bursa of the male canine hookworm (A. caninum) can be seen wrapped around the female hookworm during the act of copulation
Morphologically it is not possible to differentiate between A. duodenale and N. americanus. Interference contrast. ×400. Enlarged by 5.4.
3 the morphological differences between two species of hookworms
3.The Morphological Differences between Two species of Hookworms


A. duodenale N. americanus


Size larger smaller


Shape single curve, looks like C double curves, looks like S


Mouth 2 pairs of ventral teeth 1peir of ventral cutting plates


Copulatory circle in shape oval in shape

Bursa (a top view) (a top view)


Copulatory 1pair with separate 1pair of which unite to form

spicule endings a terminal hooklet


caudal spine present no


vulva position post-equatorial pre-equatorial



Hookworm egg

Decorticated ascaris egg

differences between decorticated ascaris and hookworm eggs
Differences between Decorticated Ascaris and Hookworm eggs


Decorticated ascaris egg hookworm egg


Shell thick thin


Egg cell unsegmented 4-8cells


Space between new moon shaped space empty space surrounding

Shell and cell between cell and ends of shell the segmented cells


ii life cycle
II. Life Cycle

1.Final host: man

2.Inf. Stage: Larva 3 or filariform larva

3.Inf. Route: by skin

4.Food: blood and tissue fluid

5.Site of inhabitation: small intestine

6.Life span: Ad 15years, Na 3-7years

7. Blood-lung migration:

skin, cavum, right heart, lungs


8. The differences between the life cycle of Ascaris and Hookworm.


A. lumbricoides Hookworm


Infective stage embryonated egg filariform larvae


route of infection by mouth by skin


mode of infection passively actively


blood-lung pass through the liver don’t pass through the liver

migration in lungs of host, larvae the larvae don’t molt and

molt twice and stay stay in the lungs

for10 days


food of the adults intestinal content blood


life span 1 year several years



Penetrate skin

Filariform larvae cavum right heart

vesseles, lymphatics

lungs(alveolus, bronchiole, bronchus) trachea, pharynx

molt3,4 deposit

duodenum adults eggs

Passed 25-30℃,moisture

outside of the body rhabditiform larvea1

In feces O2, 24hours

molt1 molt2

rhabditiform larvae2 (L2)

48hrs 6days

survive 15weeks in warm soil

filariaform(L3) wait for new hosts

iii pathogenesis and clinical manifestations
III. Pathogenesis and Clinical Manifestations

1. Larval migration

(1) Dermatitis, known as "ground itch" or "stool poison".The larvae penetrating the skin cause allergic reaction, petechiae 0r papule with itching and burning sensation. Scratching leads to secondary infection.

(2) pneumonitis (allergic reaction), Loeffier's syndrome: cough, asthma, low fever, biood-tinged sputum or hemoptysis, chest-pain, inflammation shadows in lungs under X-ray. These manifestations go on about 2 weeks.


2. Adults in small intestine

(1) Epigastric pain as that of a duodenal ulcer.

(2) A large worm burden results in microcytic hypochromatic anemia (*character manifestation). The symptoms are lassitude, edema, palpitation of the heart. In severe case, death may result from cardiac failure or physical exhaustion.

(3) Allotriophagy (or pica 异嗜症) is due to the lack of trace element iron .

(4) Amenorrhea(闭经), sterility(不孕), abortion(流产) may take place in women.

(5) Gastrointestinal bleeding

(6) Infantile hookworm disease

iv diagnosis
IV. diagnosis

Criterion: 1. hemoglobin is lower than 120g/L in man, 110g/L in woman. 2. find hookworm egg

Method: 1. saturated brine flotation technique

2. direct fecal smear

3. culture of larvae

V. Treatment

1. Albendazole 2. Mebedazole

VI. Epidemiology

worldwide distribution. 22-26℃ is the optimal temperature for Ancylostoma duodenale development, Ancylostoma duodenale mainly prevalent in north of China. 31-35℃ is suitable for Necator americanus, it is mainly prevalent in south of China

VII. Prevention

Unified measures: 1. sanitary disposal of night soil, 2. individual protection, 3. health education, 4. cultivate hygienic habits, 5. treat the patients and carriers.

enterobius vermicularis
Enterobius vermicularis

The pinworms are one of the most common intestinal nematodes. The adult worms inhabit the cecum and colon. Right after mating, the male dies. Therefore, the male worms are rarely seen. The female worms migrate out the anus depositing eggs on the perianal skin. Humans get this infection by mouth and by autoinfection.

i morphology1
I.     Morphology

1. Adults: The adults look like a pin and are white in color. The female worm measures about 8 to 13 mm in size and is fusiform in shape. The male adult is only 2-5mm. The tail of a male is curved. They die right after mating, thus males are rarely seen. The anterior end tapers and is flanked on each side by cuticular extensions called “ cephalic alae”. The esophagus is slender, terminating in a prominent posterior bulb , which is called esophageal bulb. The cephalic alae and esophageal bulb are important in identification of the species. .

2. Egg: 50 to 60m by 25 µm, persimmon seed-like, colorless and transparent, thick and asymmetric shell, content is a larva.


The cephalic alae are clearly seen at the anterior end. The cuticle and the alae are transversely striated. The oesophageal bulb are also visible.


Egg: 50 to 60m by 25 µm, persimmon seed-like, colorless and transparent, thick and asymmetric shell, content is a larva.

Anal smear showing large numbers of Enterobius eggs under the lower power. In the background are also two Ascaris eggs.
ii life cycle1
II. Life cycle

1. site of inhabitation: cecum and colon

2. infective stage: embryonated egg

3. infective route: by mouth

. 4. without intermediate host and reservoir host

5. life span of female adults: 1-2 months

migrate out anus 6hours

Adults eggs on perianal skin embryonated eggs


swallowed by hostlarvae hatch out molt

intestinal lumen adults in cecum

2-4 wks migrate down

iii symptomatology
III. Symptomatology

About one-third of pinworm-infected persons are asymptomatic, The adult worms may cause slight irritation of the intestinal mucosa.

Major symptom is anal pruritus, which associates with the nocturnal migration of the gravid females from the anus and deposition of eggs in the perianal folds of the skin. Restlessness, nervousness, and irritability, probably resulting from poor sleep associated with anal pruritus,. In young girls, migration of the worms may produce vaginitis and salpingitis or granuloma of the peritoneal cavity.

iv diagnosis1
IV. Diagnosis

Diagnosis depends on recovery of the characteristic eggs. The eggs and the female adults can be removed from the folds of the skin in the perianal regions by the use of the cellophane tape method. The examination should be made in the morning, before the patient has washed or defecated

v treatment and prevention
V.Treatment and prevention

Since the life span of the pinworm is less than two months, the major problem is reinfection. Albendazole is the drug of choice. Repeated retreatment may be necessary for a radical cure.

Prevention: 1. treat the patients and carriers 2. individual health 3. public health 4. health education and hygienic habits

  • VI. Epidemiology

Geographical distribution—cosmopolitan in temperate zones with about 30 to 50% of the population infected. It is more common in white than colored people and more prevalent in children than adults. Enterobiasis is most common where people live under crowded conditions such as orphanages, kindergartens, and large families.