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Nematode ( 线线 ) ( 线线 线线线线线 ) . Introduction to helminth and nematode . Round worm . Hook worm . Other nematodes

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Nematode (线虫 )( 教师:傅玉才教授 )

Ⅰ. Introduction to helminth and nematode

Ⅱ. Round wormⅢ. Hook wormⅣ. Other nematodes

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Introduction to helminthes

1. Definitin: Helminthes are multicellular invertebrates (worms) which may crawl by their muscle contraction. 2. Classification Nemathelminthes – Nematodes

(threadworm) Platyhelminthes-flatworms

(Cestodes,Trematodes) Acanthocephala- spiny- or thorny-headed worms

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Introduction to Nematodes1. Morphological characteristics 1) Typical nematodes are elonged, cylindrical, bilaterally symmetrical.

2) Dieocious

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Introduction to Nematodes

1. Morphological characteristics 1) Typical nematodes are elonged, cylindrical, bilaterally symmetrical. 2) Dieocious3) Protocoelom (pseudocoelom) 4) Body wall

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Introduction to Nematodes

1. Morphological characteristics4) Body wall (1) Cuticle (表皮) Epicuticle Exocuticle Mesocuticle Endocuticle (2) Hypodermis: cellular or syncytial

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Introduction to Nematodes

1. Morphological characteristics4) Body wall (1) Cuticle (2) Hypodermis (3) Musculature Meromyarian: pinworm Polymyarian: roundworm Holomyarian: whipworm

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Introduction to Nematodes

1. Morphological characteristics5) Almost all systemic organs are thread-tube-like

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Introduction to Nematodes

2. Life cycle: Egg – larva – adult 1) Egg Eggshell: (light microscopy) proteinaceous layer, chitinous, embryo membrane. (electron microscopy) vitelline layer (fertilization membrane), chitinous

lipid layer

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Introduction to Nematodes

2. Life cycle: Egg – larva – adult

1) Egg 2) Larva: Fine cylindrical in shape Molting: Larvae form a new cuticle and shed the old one. 4 molts, 4 larval stages

3) Types of life cycle (1) No intermediate host: geonematodes (direct).

(2) Requiring intermediate hosts: bionematodes (indirect)

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Ascaris lumbricoides (roundworm)

1. Morphology 1) Adult: (1) The largest nematode in human intestine, ♀, 20-35 cm long, may reach 49 cm; ♂, 15-31 cm.

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Ascaris lumbricoides

1. Morphology 1) Adult (2) Head: one dorsal and two ventrolateral lips, buccal cavity, fine denticles, papillae and cephalic sensors.

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Ascaris lumbricoides

1. Morphology 1) Adult (3) ♀: The posterior end is straight. ♂: The posterior end curves ventrally, with a pair of copulatory spicules.

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Ascaris lumbricoides

1. Morphology 2) Egg Fertilized eggs: 45-75μm by 35-50μm

Unfertilized eggs: 88-94μm by 39-44μm

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Ascaris lumbricoides

2. Life cycle

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Ascaris lumbricoides

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Ascaris lumbricoides

Summary of the life cycle

1. Location: small intestine

2. Infective stage: infective egg

3. Way of infection: through mouth

4. Larva migration:

Intestine circulatory respiratory intestine

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Ascaris lumbricoides

3. Pathogenesis 1) About 85% of ascariasis cases are symptomless 2) Pathogenesis of larva migration Mechanical trauma: Clinical manifestation: cough, fever, etc.

3) Pathogenesis of adult worms (1) Nutrition robbing and mucosa damage (2) Effects of toxin and allergen (3) Complications (due to the habits of worms’ penetrating

or wandering)

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Ascaris lumbricoides

3. Pathogenesis (3) Complications a. Biliary ascariasis b. Intestinal penetration c. Intestinal obstruction

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Ascaris lumbricoides

4. Diagnosis

1) Etiological examination Direct fecal smear:

1 smear, 80% positive; 3 smears, 95%.

2) Why can not we detect any egg in a few cases ?

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Ascaris lumbricoides

5. Epidemiology 1) Epidemiological characteristics and epidemic conditions Source of infection Way of transmission Susceptible population 2) Factors causing extensive distribution of the infection (1) Factors from the worm: a. 200,000 eggs daily/per female b. Egg resistance c. Life cycle is direct (geonematode)

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Ascaris lumbricoides

5. Epidemiology

2) Factors causing extensive distribution of the infection (1) Factors from the worm (2) Factors from man a. Poor sanitation b. Vegetable contaminated c. Others

6. Prevention and treatment

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Ancylostoma duodenale Necator americanus

(hookworm)

Worldwide distribution Intestinal parasitesCausing host blood loss (anemia)

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Hookworm

1. Morphology 1) Adults: small nematode, about 1.0 cm in

length Appearance: A. duodenale “C” shaped N. americanus “S” shaped

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Hookworm

1. Morphology 1) Adults Buccal capsule A. duodenale: 2 pairs of ventral teeth N. americanus: 1 pair of ventral semilunar cutting plates

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Hookworm

1. Morphology 1) Adults ♀: the posterior end is cone-shaped ♂: elliptic and fan-shaped (copulatory bursa)

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Hookworm

1. Morphology 1) Adults Characteristics of copulatory spicules

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Hookworm

1. Morphology 1) Adult Internal structure:

Function of glands:

(1) A pair of cephalic glands open into cephalic sensors, secrete anticoagulant and acetylcholine esterase.

(2) 3 pharyngeal glands open into the buccal cavity and pharyngeal cavity, secrete acetylcholine esterase and proteinases

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Hookworm

1. Morphology 2) Egg: 64-75μm by 34-40μm 1-8 cells or an embryo Shells are thin and hyaline.

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Hookworm

2. Life cycle

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Summary of life cycle

1. Location: small intestine2. Infective stage: filariform larvae3. Infection way: through skin4. Larva migration: skin circulatory respiratory

intestine

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3. Pathogenesis

1. Pathogenesis of the larvae (1) Dermatitis (“ground itch”) due to working in farmland, contacting

with the soil Susceptible locations: between fingers

and toes (2) Symptoms caused by larva

migration from pulmonary capillaries to alveoli a dry cough, sore throat, severe

hemorrhage, etc

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3. Pathogenesis

1. Pathogenesis of the larvae2. Pathogenesis of the adults Worms burrow through the mucosa with

buccal capsule,

teeth, cutting plates, feed on blood, secret anticoagulants and proteinases Worms continuously suck blood, but

digest a little, the large amount of blood is

passed. Worms change places and leave the

wound bleeding.

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3. Pathogenesis2. Pathogenesis of the adults (1) Anemia The amount of blood loss N. americanus: 0.02~0.10 ml per worm a

day A. duodenale: 0.14~0.26 ml per worm a day Nature of the anemia: hypochromic microcytic

anemia (2) Gastrointestinal symptoms Epigastric discomfort, secret anguish(痛苦 ), or

pain Nausea, vomiting, diarrhea, etc Aberrations of appetite(异嗜症 )

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4. Diagnosis

1. Direct fecal smear2. Floatation of saturation NaCl

solution3. Culture of hookworm larvae

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5. Epidemiology and Control

Self-teaching