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Nematode II. Main contents of last time. A. Trichinella spiralis (The trichina worm) B. Trichuris trichiura (Whipworm) C. Capillaria philippinensis D. Strongyloides stercoralis E. Hookworms
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Main contents of last time A.Trichinella spiralis (The trichina worm) B. Trichuris trichiura(Whipworm) C. Capillaria philippinensis D. Strongyloides stercoralis E. Hookworms (A,B,C,E.Obligatory; D.Facultative; A.Biohelminth; A.Tissue nematode; B~E. Intestine nematode)
Trichinella spiralis: • Pathogen of trichinosis; • Biohelminth; • Ovoviviparous; • Need change host to complete its life cycle; • Infective / diagnostic stage: encysted larvae (nurse cell-parasite complex) • Main pathogenic stage: larvae.
Trichuris trichiura ( Whipworm): • Pathogen of trichuriasis; • Site of inhabitation: cecum; • Infective stage: embryonic egg; • Infective mode and route: passively swallowed by the mouth; • Geohelminth.
Capillaria philippinensis • Pathogen of intestinal capillariasis; • It causes a severe protein-losing enteropathy and malabsorption syndrome, with a relatively high mortality unless appropriate therapy is instituted. • The ova must be distinguished from those of Trichuris trichiura which they superficially resemble.
Strongyloides stercoralis • Pathogen of strongyloidiasis; • Free living parasitic nematode of the small intestine of humans and animals; • Infection in immunocompetent hosts and immunocompromied host; • Infection and autoinfection; • Gastrointesinal and respiratory symptoms; • Geohelminth; • Facultative parasite.
Hookworms: Ancylostoma duodenale & Necator americanus Geohelminths; Site of inhabitation: small intestine; Final host: man; Inf. stage: Larva 3 or filariform larva; Inf. route: by skin; Food: blood and tissue fluid; Blood-lung migration: skin, right heart, lungs, intestine.
I Enterobius vermicularis • Thepinwormsare one of the most common intestinal nematodes. The adult worms inhabit the cecum and colon. Right after mating, the male dies. The female worms migrate out the anus depositing eggs on the perianal skin.Humans get this infection by mouth and by autoinfection.
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 2-5 mm. 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.
Anterior part of E. vermicularis. Note cephalic alae and esophageal bulb .
2 Egg: 50 to 60µm 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 Main points of its 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
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.
There are symptoms like 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 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.
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.
II. Ascaris lumbricoides Ascaris lumbricoides , common saying “roundworm of man”, is the largest of the intestinal nematodes parasitizing humans. It is the most common worm found in human. It is worldwide in distribution and most prevalent through out the tropics, subtropics and more prevalent in the countryside than in the city.
Morphology • Adult: The adults are cylindrical in shape, creamy-white or pinkish in color. The female averages 20-35 cm in length, the largest 49 cm. The male is smaller, averaging 15-31cm in length and distinctly more slender than the female, and has a typical curled tail with a pair of sickle-like copulatory spines.
On the tip of the head there are three lips, arranged triangularly (dorsal lip and 2 ventral lips). They have a complete digestive tract. Reproductive organs are tubular, male has a single reproductive tubule while the female has two and the vulva is ventrally located at the posterior part of the anterior 1/3 of the body.
The lips of Ascaris lumbricoides 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 two kinds of the eggs: fertilized eggs and unfertilized eggs. We usually describe an egg in 5 aspects: -- size; -- color; -- shape; -- shell and -- content.
1. Fertilized eggs: broad oval in shape, brown in color, an average size 60× 45 µm. The shell is thicker and consists of ascaroside, chitinous layer, fertilizing membrane and albuminous coat stained brown by bile. The content is a fertilized ovum. There is a new-moon(crescent) shaped clear space at each end inside the shell.
2. 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. Both fertilized and unfertilized eggs sometimes may lack their outer albuminous coats and are colorless.
Fertilized Ascaris Egg A fertilized Ascaris egg, still at the unicellular stage, as they are when passed in stool. Normally eggs are at this stage when passed in stool.
Fertilized Ascaris Egg The ova begin fission
Freshly Passed Ascaris Eggs From faeces • The eggs may appear from light to dark brown in color.
Egg containing a larva, which will be infective if ingested.
Life Cycle Main points of its life cycle: 1.Site of inhabitation: small intestine 2. Infective stage: embryonated eggs 3. Route of infection: by mouth 4. No intermediate and reservoir hosts 5. Life span of the adult: about 1 year
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 10-14 days 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.
swallowed digestive Infective eggs small intestine Larvae hatch out juice act penetrate Lymphatic or venules Liver intestine mucosa penetrate the molt2,3 Right heart lungs Alveoli alveolar wall Bronchiles Bronchi Trachea discharged with sputum die return to molt 4 Pharynx Small intestine Adults discharged 25-30℃,moisture Fertilized eggs Out side of in feces the body 2-3weeks, molt1 Embryonated eggs(infective eggs)
Pathogenesis 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 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 (1)intestinal obstruction, (2)appendicitis, (3)biliary ascariasis, (4)perforation of the intestine, (5)cholecystitis, (6)pancreatitis and (7)peritonitis, etc., may occur, in which biliary ascariasis is the most common complication.
