Hookworm

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 and Ancylostoma duodenale. They live in small intestine.

Morfology

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.

Eggs: 60×40 µm in size, oval in shape, shell is thin and colorless.

Content is 2-8cells.

The Morphological Differences between Two species of Hookworms

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A. duodenale N. americanus

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Size larger smaller

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

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

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Copulatory circle in shape oval in shape

Bursa (a top view) (a top view)

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

spicule endings a terminal hooklet

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caudal spine present no

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vulva position post-equatorial pre-equatorial

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Lyfe 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

nPathogenesis & Clinical manifestation

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.

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 (orpica) is due to the lack of trace element iron (4) Amenorrhea, sterility, abortionmay take place in women.

(5) Gastrointestinal bleeding

(6) Infantile hookworm disease

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

Treatment

1. Albendazole
2. Mebedazole

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

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 (Pinworm)

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.


Morfology

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.

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.

Life cycle

site of inhabitation: cecum and colon , infective stage: embryonated egg and infective route: by mouth, without intermediate host and reservoir host, life span of female adults: 1-2 months.

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.

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.

Treatment & 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

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.

Trichuris trichiura

Morphology

Adult: the worm looks like a buggy whip, the anterior 3/5 is slender and the posterior 2/5 is thick. It is pinkish gray in color. The female worm is 3-5 cm in length and has a long slender esophageal region. The male is smaller than the female and has a curved tail. The reproductive organs of male and female are all double tubule.

Egg: it is barrel or spindle in shape and 50 x 20µm in size. It is brownish and has a translucent polar plug at either ends. The content of the egg is an undeveloped cell


Life cycle

Female releases 1000 to 7000 unembryonated double-plugged eggs each day.Eggs are deposited onto warm, moist shady soil where they embryonate to the L1 stage.

The emrionate egg is the infective stage and is ingested. L1 hatch from the egg in the small intestine and burrow into the mucosa where they are. Adults migrate to the ileocecal and colon regions. Adult worm is inserted into the wall of the intestine penetrating through the mucosa and into the submucosa where blood is ingested.

Pathogenesis:

1.Light infection: Asymptomatic

2.Middle infection: Clinical manifestations are usually abdominal pain, anorexia, diarrhea, constipation .

3. Heavy infection: Bloody diarrhea, emaciation, prolapse of the anus may occur.

Diagnosis:

Discover the eggs in feces by saturated brine flotation method or direct fecal smear.

Treatment and prevention: Same as those of ascariasis Take Mebendazole 3 days for a treatment course and repeat next week

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Ascaris lumbricoides

HOSPES & DISEASE NAME

Ascaris lumbricoides, common saying 'soil transmitted helmint' is the largest of the intestinal nematodes parasitizing humans. It has worldwide in distribution and most prevalent through out the tropics,subtropic,and more prevalent in the countryside than in the city.The disease's name is ascariasis.

¨MORFOLOGY

Adult: The adults are cylindrical in shape, creamy-white or pinkish in color. The female averages 20-35cm in length, the largest 49cm. The male is smaller, averaging 15-31cm in length and distinctly more slender than the female. The typical curled tail with a pair sickle like copulatory spines. On the tip of the head there are three lips, arranged as "a Chinese word “ 品They have a complete digestive tract. Reproductive organs are tubular. male has a single reproductive tubule. The female has two reproductive tubules and the vulva is ventrally located at the posterior part of the anterior 1/3 of the body. The three lips are seen at the anterior end. The margin of each lip is lined with minute teeth which are not visible at this magnification.

Egg : There are three type of the eggs. They are fertilized eggs, unfertilized eggs and decorticated eggs. We usually describe an egg in 5 aspects: size, color, shape, shell and content.

Fertilized eggs: broad oval in shape, brown in color, an average size 60× 45µm. The shell is thicker and consists of ascaroside, chitinous layer, fertilizing membrane and mammillated albuminous coat stained brown by bile. The content is a fertilized ovum. There is a new-moon(crescent) shaped clear space at the each end inside the shell.

Unfertilized egg: Longer and slender than a fertilized egg. The chitinous layer and albuminous coat are thinner than those of the fertilized eggs without ascaroside and fertilizing membrane. The content is made of many refractable granules various in size.

Decorticated eggs: Both fertilized and unfertilized eggs sometimes may lack their outer albuminous coats and are colorless.


LIFE CYCLE

This worm lives in the lumen of small intestine, feeding on the intestinal contents, where the fertilized female lays eggs. An adult female can produce approximately 240,000 eggs per day, which are passed in feces. When passed, the eggs are unsegmented and require outside development of about three weeks until a motile embryo is formed within the egg.

After the ingestion of embryonated eggs in contaminated food or drink or from contaminated fingers, host digestive juices acts on the egg shell and liberate the larva into the small intestine. These larvae penetrate the intestinal mucosa and enter lymphatics and mesenteric vessels. They are carried by circulation to the liver, right heart and finally to the lungs where they penetrate the capillaries into the alveoli in which they molt twice and stay for 10-14days and then they are carried, or migrate, up the bronchioles, bronchi, and trachea to the epiglottis. When swallowed, the larvae pass down into the small intestine where they develop into adults. The time from the ingestion of embryonated eggs to oviposition by the females is about 60-75 days. The adult worms live for about one year. The ascarid life cycle is as the following diagram.


Pathogenitas

There are two phase in ascariasis:

1. The blood-lung migration phase of the larvae: During the migration through the lungs, the larvae may cause a pneumonia. The symptoms of the pneumonia are low fever, cough, blood-tinged sputum, asthma. Large numbers of worms may give rise to allergic symptoms. Eosionophilia is generally present. These clinical manifestation is also called Loeffler’s syndrome.
2. The intestinal phase of the adults. The presence of a few adult worms in the lumen of the small intestine usually produces no symptoms, but may give rise to vague abdominal pains or intermittent colic, especially in children. A heavy worm burden can result in malnutrition. More serious manifestations have been observed. Wandering adults may block the appendical lumen or the common bile duct and even perforate the intestinal wall. Thus complications of ascariasis, such as intestinal obstruction, appendicitis, biliary ascariasis, perforation of the intestine, cholecystitis, pancreatitis and peritonitis, etc., may occur, in which biliary ascariasis is the most common complication.

Diagnosis

¨ The symptoms and signs are for reference only. The confirmative diagnosis depends on the recovery and identification of the worm or its egg.

1. Ascaris pneumonitis: examination of sputum for Ascaris larvae is sometimes successful.

2. Intestinal ascariasis: feces are examined for the ascaris eggs.

(1) direct fecal film: it is simple and effective. The eggs are easily found using this way due to a large number of the female oviposition, approximately 240,000 eggs per worm per day. So this method is the first choice.
(2) brine-floatation method:

(3) recovery of adult worms: when adults or adolescents are found in feces or vomit and tissues and organs from the human infected with ascarids , the diagnosis may be defined.