Nematodes ( 线 虫 )

Content:

I. Introduction

II. Ascaris lumbricoides （蛔虫）III. Trichuris trichiura （鞭虫）IV. Enterobius vermicularis （蛲虫）V. Hookworms （钩虫 )VI. Trichinella spiralis （旋毛虫）VII. Filariar （丝虫）

I. Introduction to Nematode

Medical Parasitology

Protozoa Helminths Arthropoda

Trematoda Nematode Cestoidea Acanthocephala ( 吸虫 ) ( 线 虫 ） （绦 虫 ） （棘头虫 ）

Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis

Hookworms, Trichinella spiralis, Filariar

1. Morphology of nematodes

1) General morphology

(1) Tubular in shape and

bilaterally symmetrical

(2) With a complete digestive

canal

(3) Adult worm separated in

male and female

2) Body wall

The body wall of nematodes

is covered:

• Cuticle （角皮层）• Hypodermis （皮下

层）• Musculature （肌层）

Cuticle formed some special constructions, theyhave special functions and are very important toidentify the species of nematodes

for examples: • Buccal capsule ( 口囊 )

• Copulatory bursa ( 交合伞 )

• Spicule ( 交合刺 ) • Alae ( 翼）• Papillae ( 乳头）

copulatory

bursa( 交合伞 )

alae

papillae

Spicule

3) Digestive system

It is complete with

mouth, esophagus, intestine and anus

4) Reproductive systemMost nematodes are separatedin male and female

(1) male reproductive system Testis seminal vesicle ( 睾丸） （储精囊） vas deferens ejaculatory duct （输精管） （射精管）

(2) Female Reproductive System 

Most females usually have two

ovaries,oviducts and uterus..

ovary—oviduct —uterus..

vagina-vulva

ovary—oviduct —uterus.. （ 阴 道 ） ( 阴门）

（卵巢） （输卵管） （子宫）

5) Reproductive mode

• Oviparous ( 卵生 )

• Ovoviviparous ( 卵胎生）

2. Life cycle

The four juvenile stages and ecdysis (molting

of cuticle 蜕皮） .

ecdysisEggs Larvae(4 stages) adults

(male & femal)

6) egg ： the shell consists of 3 layers

Vitelline layer ( 卵黄膜 ),

Chitinous layer ( 壳质层 )

Ovum or embryo

Lipid layer ( 蛔甙层 )

Kinds of life cycle in nematodes

1) Direct life cycle:

in which the parasite is passed from host to the next through the contaminated food or water. Intermediate host is not necessary to these parasites

Ascaris lumbricoides

Trichuris trichiura

Enterobius vermicularis

Hookworms

2) Indirect life cycle:

intermediate host is necessary in this

style of life cycle

Trichinella spiralis

Filaria

3. Pathology

1)Larvae ： ( 1) dermatitis caused by cutaneous invasion an

d subcutaneous migration of larva;

( 2) injury to organs or tissues by migration of l

arvae in the body

2) Adults ： (1) injury to intestinal mucosa caused by

the parasites living in gastro- intestinal

system

(2) injury to lymphatic system, muscles or

nervous system caused by the parasites

living in tissues

Ascaris lumbricoides ( 蛔虫 )

The common name of Ascaris lumbricoides is “round worm” ， it is the largest nematode and the adults live in intestine of human, cause Ascariasis ( 蛔虫病 ) ；

The morbidity in whole world is estimated at 1 billion , the infective rate of the population in China is about 44.9% to 71% ；

The round worms of cat (Toxocara cati) and dog (Toxocara canis) can result in larval migrans in human

1. Morphology

1) The largest of intestinal nematode;

resembling an earthworm;

living worms show reddish colour;

2) Three lips around the mouth in “ 品” type and possess small teeth

Comparison of different nematodes in size

3 ） How to identify male and female

• Male: measuring 25cm long ，

posterior extremity curved in the form of a hook

• Female: measuring 35cm long, posterior extremity is straight

4) How to identify the eggs:

• Fertilized eggs are oval to round, the shell is thick and with protein coat ( 蛋白质膜 ). An ovum in the shell.

• Unfertilized egg is more elongated, thinner shell with small protein coat and an atrophied ovum marked by refractile granules.

Protein coat

Chitin layer

Fertilized egg Unfertilized egg

Fertilized egg losing

of protein coat

ovum

refractile granules

The resistance of Ascaris eggs to chemicals is very strong. They can embryonate successfully in 10 formalin, potassium dichromate (KCl), ﹪ hydrochloric acid (HCl), nitric acid, acetic acid,

and sulfuric acid(H2SO4)

This extraordinary chemical resistance is the result of the lipid layer of the eggshell

Resistance of eggs to chemicals

3. Life cycle

adults

(intestine ） eggs

240000/day

（ feces ） eggs

moist 、 shady

warm, O2, 2w infective eggs

larvae

Adults

(intestine)

penetrate intestine wall —blood—liver—right heart

— lungs—respiratory tree—pharynx —intestine

Larvae migrate in the circulation system

ingest

(hatch in up

small intestine ）

4. Pathology

1) larvae:

• Ascaris Pneumonitis :caused by the penetration of larvae in l

ung’s capillaries

During the pulmonary stage, there may be a brief period of co

ugh, fever, expectoration ( 咳痰 ) , sputum with blood • Asthma:caused by the metabolites of the parasites

Ascaris lumbricoides larva in section of lung

2) Adults ： (1) Malnutrition:

adults take liquid contents of intestine as their food;

damage of mucosa of intestine causing

malabsorption

(2) Disorder of digestive system:

• abdominal pain

• anorexia ( 食欲不振 )

• nausea ( 恶心 )

• vomiting ( 呕吐 )

• diarrhea ( 腹泻 )

• intestinal obstruction

.

3 ） Allergic responses to metabolites produced by the worms

• rashes( 荨麻疹 )

• Asthma

• Restlessness （烦躁不安）

• insomnia( 失眠 )

• angioneuro-edema( 血管神经性水肿 )

• optic neuritis ( 视神经炎 )

• Conjunctivitis ( 结膜炎 )

4 ） Complication( 并发症 ) ：• Adults have a special

characteristic----”penetration of hole”

• Cause many different complications due to the penetration

(1) penetrate to the appendix and causes appendicitis (2) penetrate to the pancreatic and bile ducts

cause grave results.

Ascaris in pancreas and bile duct

Empyema

of chest

Adults in

bile duct

detected by

B-ultrasound

(3) intestinal obstruction caused by massive infection

(4) Worms reaching the stomach often cause nausea

(5) Worms that reach the esophagus may crawl into

the trachea, causing suffocation （窒息） (6) They may crawl into the middle ears, causing

extensive damage

(7) They may simply exit through the nose or mouth

5. Diagnosis

1) By identifying the adults passed

2) By identifying the eggs in the feces

6. Epidemiology and control

1. Epidemiology: this disease is very wides

pread

Worldwide over 1 billion

persons are infected.

44.9% to 71% of

population are infected

with the parasite in China

Why?

1) Profuse production of eggs (? / per day,per female)

2) Egg’s resistance to chemical and environmental condition;remains viable for about 1 year in the field

3) Nightsoil is used as fertilizer

4) Low personal hygiene (3F)

5) Poor sanitation

2)Treatment and Prevention:

• Mebendazole （甲苯达唑）： 200 mg, for adults and 100 mg for children, for

3 days is effective.

• Albendazole （阿苯达唑）： 400mg/d ， 1~2d

• Good hygiene is the best preventive measure

Trichuris trichiura ( 毛首鞭形线虫 )

1. Introduction:

The common name of

Trichuris trichiura is

whip-worm( 鞭虫 ), adults

live in caecum ( 盲肠 ) of

human and result in

trichuriasis( 鞭虫病 )

2. Morphology:

1) Adults resemble a whip, anterior with a hair-like lash and posterior with the handle.

Mouth cavity is provided with a minute spear

2) Male: about 4 cm long, posterior is spirally coiled.

3) Female: about 5 cm long, posterior extremity straight.

4) Egg

(1)A typical barrel shape with two polar plugs (2) Size: 50-54 µm by 22-23 µm (3)The external layer of the

shell of the egg is yellow brown

(4) An ovum is in the egg when it passed with sto

ol

3. Life cycle

adults（ cecum ）

eggs1T~7T/daily moist 、 warm

3~5w

infective eggs

larvae （ small intestine ）

adults （ cecum ）

migration down cecum

Larvae do not enter circulation system ！

ingestion

4. Pathology

• Feeding on tissue fluid and blood;

• The slender anterior ends penetrate into the gut mucosa and make lesions;

Symptoms:Symptoms are determined largely by the wormburden: • light infections are asymptomatic. • Heavier infections are characterized by: 1) chronic mucous and bloody diarrhea 2) abdominal pains 3) hemorrhage and anemia ( 贫血 ) or rectal prolapse ( 直肠脱垂 ) in heavy infection children 4) The infection may result in malnutrition and growth retardation

5. Diagnosis

• Diagnosis is based on symptoms and the presence of eggs in feces

6. Prevalence and control

• Trichuriasis often prevail with ascariasis

• 17.38% of population infected with this

parasite in China

• The treatment and control can refer to ascariasis

Hookworm ( 钩虫）

Adults live in the intestine and take blood from the host, cause hookworm disease

Species of Hookworm

• Human hookworms:

1) Ancylostoma duodenale ( 十二指肠钩口线虫 , 十二指肠钩虫 )

2) Necator americanous ( 美洲板口线虫 , 美洲钩虫）• Animal hookworms:

1) Ancylostoma ceylanicum ( 锡兰钩口线虫 )

2) Ancylostoma caninum ( 犬钩口线虫 )

3) Ancylostoma braziliense ( 巴西钩口线虫 )

(caused cutaneous larval migrans)

Teaching objectives

Ancylostoma duodenale and Necator americanes 1. Morphology 2. Life cycle 3. Pathology and clinical manifestations4. Diagnosis5. Prevalence and control

2. Morphology

1) How to identify adults of A. duodenale and N. americanes

2) How to identify the eggs

Different between A. duodenale and N.americanus

A. duodenale N. americanus

1) shape “C”, 1cm + “S”, 1cm+

2) buccal capsule flat and oval-shape; oval-shape; two pairs one pair cutting plates3) copulatory bursa round oblate 4) Spicule two,separated two, fused at their ends

buccal capsule

and teeth

shape

spicule

A. duodenale N. americanus

C S

Flat and oval oval

round oblate

copulatory bursa

Identify the egg• Shape: oval-round • Shell: thin and colorless• Size: 57-76 µm by 35-47 µm• Contains: clear space between the egg-shell and the ovum. One ovum in the fresh egg but 2 to 8 cells in constipated ( 便秘） stools

Eggs of A. duodenale and N. americanus can not be distinguished morphologically

3. Life cycle

adults(intestine)

——— eggs10000/daily

（ feace)

w & m

Shade,O2,24h

—— 1st larvae ——2nd larvaeecdysis

48h

—— filariform

ecdysis

5~6d

skin—blood—heart—lungs—pulmonary alveolae—

bronchial tree —pharynx—stomach—small intestine

————————————

—— adults

（ small intestine ）

Larvae migrate in the

circulation system

•Taxis （趋性） of infective larvae (filariform):

1 ） Thermotaxis

2 ） Negative attraction to gravitation

3 ） Positive attraction to pressure

•Route of infection

1 ） Skin

2 ） Oral （ A. doudenale)

3 ） Placenta

4 ） Mother’s milk

5 ） Paratenic hosts （ A. doudenale can be

transmitted through ingestion of

undercooked meat,including beef,

lamb, pork,rabbit )

4. Pathogenesis

Hookworm disease manifests three main phases ofpathogenesis:

1) the cutaneous or invasion phase, 2) the migration or pulmonary phase, 3) the intestinal phase.

  

1) Cutaneous phase

The cutaneous phase begins when filariforms penetrate

the skin and cause ground itch ( 钩蚴性皮炎 )

       

2) Pulmonary phase

The pulmonary phase occurs when the juvenilesbreak out of the lung capillaries into the alveoli and progress up the bronchi. Each sitehemorrhages slightly, with serious consequences inheavy infections;

During this phase, there may be a brief period ofcough, fever, expectoration, sputum with blood,

asthma or pneumonitis may occur

3) Intestinal phase

• The worm attaches to the mucosa with its strong buccal capsule and teeth, and it begins to feed on blood.• The worms often change their bite places and mak

e more lesions.• More blood through their digestive tracts than tha

t of their necessary for their nutrition (for getting oxygen from blood )

 

worm attaches to the mucosa with its strong buccal capsule and teeth, and it begins to feedon blood

• Blood loss per worm is

about 0.03ml per day for

Necator and about 0.26

ml per day for Ancylostoma

• Patients with heavy

infections may lost up to

200 ml of blood per day

Symptoms in moderate infections

• gradually produce an iron-deficiency anemia

• Slight, intermittent abdominal pain,

• loss of normal appetite and desire to eat soil (geophagy 异嗜症 ) or un-normal materials

In heavy infections:

• patients suffer severe protein deficiency, with dry skin and hair, edema

• potbelly in children and with delayed puberty, mental dullness, heart failure and death.

• in the young, often causes stunted growth and below-average intelligence.

4.Diagnosis

• Stool examination:based on finding of the characteristic egg

• Larval cultivation( 钩蚴培养法 ) :based on finding of hatched larvae

5. Epidemiology

• Hookworms parasitize more than 900 million people in the world and cause daily blood loss of 7 million liter

• 194 million people are infected with hookworms in China

• N. americanes is most common in south of China. A. duodenale is most common in north of China

Factors of prevalence

• Warmer and poor sanitation

• Inadequate disposal of faeces

• Using nightsoil as fertilizer

• Bare-foot walking

• Occupation: Miners and peasants who plant coffee,vegetable,sweet-potato,corn (dry-plants)

• Mebendazole, 200 mg, for adults and 100 mg for children, for 3 days is effective.

• Sanitation is the chief method of control: sanitary disposal of fecal material and avoidance of contact with infected fecal material.