1. 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）

2. 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

3. 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

4. 2) Body wall The body wall of nematodes is covered: Cuticle （角皮层）
Hypodermis （皮下层）
Musculature （肌层）

5. Cuticle formed some special constructions, they
have special functions and are very important to
identify the species of nematodes
for examples:
Buccal capsule (口囊)
Copulatory bursa (交合伞)
Spicule (交合刺)
Alae (翼）
Papillae (乳头）

6. alae
papillae
Spicule
copulatory
bursa(交合伞)

8. 2) Pseudocoelom (false body cavity: a cavity between the body wall and digestive canal, a membrane around digestive canal is abscent

9. 3) Digestive system It is complete with
mouth, esophagus, intestine and anus

10. 4) Reproductive system Most nematodes are separated in 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）

11. (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）

12. 5) Reproductive mode
Oviparous (卵生)
Ovoviviparous (卵胎生）

13. 2. Life cycle The four juvenile stages and ecdysis (molting
of cuticle 蜕皮）.
ecdysis
Eggs Larvae(4 stages) adults
(male & femal)

14. 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)

15. Kinds of life cycle in nematodes
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

16. 2) Indirect life cycle:
intermediate host is necessary in this
style of life cycle
Trichinella spiralis
Filaria

17. 3. Pathology
1)Larvae：
( 1) dermatitis caused by cutaneous invasion and subcutaneous migration of larva;
( 2) injury to organs or tissues by migration of larvae in the body

18. 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

19. 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

20. 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

21. Comparison of different nematodes in size

23. 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

24. 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.
refractile granules
Protein coat
ovum
Chitin layer
Fertilized egg losing
of protein coat
Fertilized egg
Unfertilized egg

25. Resistance of eggs to chemicals
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

26. Larvae migrate in the circulation system
3. Life cycle
240000/day
（feces）
moist、shady
warm, O2, 2w
ingest
(hatch in up
small intestine）
eggs
adults
(intestine）
eggs
infective eggs
penetrate intestine wall —blood—liver—right heart
— lungs—respiratory tree—pharynx —intestine
larvae
Adults
(intestine)
Larvae migrate in the circulation system

28. Summary of Life Cycle
Adult worms (1) live in the lumen of the small intestine. A female may
produce up to 240,000 eggs per day, which are passed with the feces (2).
Fertile eggs embryonate and become infective after 18 days to several weeks
(3), depending on the environmental conditions (optimum: moist, warm,
shaded soil). After infective eggs are swallowed (4), the larvae hatch (5),
invade the intestinal mucosa, and are carried via the portal, then systemic
circulation to the lungs (6). The larvae mature further in the lungs (10 to 14
days), penetrate the alveolar walls, ascend the bronchial tree to the throat,
and are swallowed (7). Upon reaching the small intestine, they develop into
adult worms (1). Between 2 and 3 months are required from ingestion of the
infective eggs to oviposition by the adult female. Adult worms can live 1 to 2
years.

29. 4. Pathology
larvae:
Ascaris Pneumonitis :caused by the penetration of larvae in lung’s capillaries
During the pulmonary stage, there may be a brief period of cough, fever, expectoration (咳痰) , sputum with blood
Asthma:caused by the metabolites of the parasites

30. Ascaris lumbricoides larva in section of lung

31. . 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 .

32. 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)

33. 4）Complication(并发症)：
Adults have a special characteristic----”penetration of hole”
Cause many different complications due to the penetration

34. Ascaris in pancreas and bile duct
(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

35. Empyema
of chest
Adults in
bile duct
detected by
B-ultrasound

36. (3) intestinal obstruction caused by massive infection

37. (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

38. 5. Diagnosis By identifying the adults passed
By identifying the eggs in the feces

39. 6. Epidemiology and control
this disease is very widespread
Worldwide over 1 billion
persons are infected.
44.9% to 71% of
population are infected
with the parasite in China
Why?

40. Profuse production of eggs (? / per day,per female)
Egg’s resistance to chemical and environmental condition;remains viable for about 1 year in the field
Nightsoil is used as fertilizer
Low personal hygiene (3F)
Poor sanitation

41. 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

42. 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)

43. 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.

44. 4) Egg A typical barrel shape with two polar plugs
(2) Size: 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 stool

45. Larvae do not enter circulation system！
3. Life cycle
1T~7T/daily
moist、warm
3~5w
adults
（cecum）
eggs
infective eggs
ingestion
migration down cecum
larvae
（small intestine）
adults
（cecum）
Larvae do not enter circulation system！

47. 4. Pathology Feeding on tissue fluid and blood;
The slender anterior ends penetrate into the gut mucosa and make lesions;

48. Symptoms: Symptoms are determined largely by the worm burden:
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

49. 5. Diagnosis
Diagnosis is based on symptoms and the presence of eggs in feces

50. 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

51. Hookworm (钩虫）
Adults live in the intestine and take blood from the host, cause hookworm disease

52. 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)

53. Teaching objectives Ancylostoma duodenale and Necator americanes
Morphology
Life cycle
Pathology and clinical manifestations
Diagnosis
Prevalence and control

54. 2. Morphology
1) How to identify adults of A. duodenale and N. americanes
2) How to identify the eggs

55. 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 plates
3) copulatory bursa round oblate
4) Spicule two,separated two, fused at
their ends

56. A. duodenale S C N. americanus shape buccal capsule and teeth
Flat and oval
oval
spicule
copulatory bursa
round
oblate

57. Identify the egg Eggs of A. duodenale and N. americanus can not
Shape: oval-round
Shell: thin and colorless
Size: µm by 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

58. 3. Life cycle adults ——— eggs —— 1st larvae ——2nd larvae ————————————
10000/daily
（feace)
w & m
Shade,O2,24h
ecdysis
48h
adults
(intestine)
——— eggs
—— 1st larvae
——2nd larvae
skin—blood—heart—lungs—pulmonary alveolae—
bronchial tree —pharynx—stomach—small intestine
ecdysis
5~6d
—— filariform
————————————
—— adults
（small intestine）
Larvae migrate in the
circulation system

59. Taxis（趋性） of infective larvae (filariform):
1）Thermotaxis
2）Negative attraction to gravitation
3）Positive attraction to pressure

60. 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 )

61. Habit of adults and blood loss of host
1）Blood-sucking habit
2）Cutting organs: teeth or plates
3）Anticoagulant: secreted by glands of the worm
4）Pumping blood out by esophageal muscles
5）Blood passing through the worm’s intestine
quickly (half to several minutes)
6）Frequently changing of bite position(4 sites
/24h)

63. Life cycle
Adult worms live in the lumen of the small intestine, where they attach to the intestinal
wall with resultant host blood loss. Eggs are passed in the stool, and under favorable
conditions (moisture, warmth, shade), hatch in 1 to 2 days. Larvae are released, grow in
the feces and/or the soil, and after 5 to 10 days (and two molts) have become filariform
(L-3) larvae that are infective. These infective larvae can survive 3 to 4 weeks in
favorable environments. On contact with the human host, the larvae penetrate the skin
and are carried through the veins and the heart to the lungs. They penetrate into the
pulmonary alveolae, ascend the bronchial tree to the pharynx, and are swallowed. Upon
reaching the small intestine, they undergo two more molts yielding fourth stage larvae
(L4) and then adult worms. Five weeks or more are required from invasion by the L3 to
oviposition by the adult female. Most adult worms are eliminated in 1 to 2 years, but
longevity records can reach several years. Some A.duodenale larvae, following
penetration of the host skin, can become dormant (in the intestine or muscle!). In
addition, infection by A.duodenale may probably also occur by the oral and
transmammary route.(N. americanus, however, requires a transpulmonary migration
phase.) 

64. 4. Pathogenesis Hookworm disease manifests three main phases of
1) the cutaneous or invasion phase,
2) the migration or pulmonary phase,
3) the intestinal phase.

65. 1) Cutaneous phase
The cutaneous phase begins when filariforms penetrate
the skin and cause ground itch ( 钩蚴性皮炎)
       

66. 2) Pulmonary phase The pulmonary phase occurs when the juveniles
break out of the lung capillaries into the alveoli
and progress up the bronchi. Each site
hemorrhages slightly, with serious consequences in
heavy infections;
During this phase, there may be a brief period of
cough, fever, expectoration, sputum with blood,
asthma or pneumonitis may occur

67. 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 make more lesions.
More blood through their digestive tracts than that of their necessary for their nutrition (for getting oxygen from blood )

68. ml per day for Ancylostoma
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
worm attaches to the mucosa with its strong buccal capsule and teeth, and it begins to feed on blood

69. 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

70. 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.

71. Summary Site Symptoms Pathogenesis
Dermal Local erythema, macules, Cutaneous invasion and
papules (ground itch) subcutaneous migration of
larva
Pulmonary Bronchitis, pneumonitis, Migration of larvae through
and eosinophilia lung, bronchi, and trachea
Gastro Anorexia, epigastric pain Attachment of adult worms
intestinal and gastro-intestinal and injury to upper
hemorrhage intestinal mucosa
Hemato- Iron deficiency, anemia, Intestinal blood loss
logic hypoproteinemia, edema,
cardiac failure

72. 4.Diagnosis
Stool examination:based on finding of the characteristic egg
Larval cultivation(钩蚴培养法) :based on finding of hatched larvae

73. 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

74. 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)

75. 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.