Introduction to the Helminths 蠕虫

Helminths means worms, multicellular organisms.

Phylum Class

Nemathelminthes Nematoda(round worm) 线虫纲 线形动物门 Platyhelminthes Tremetoda(flatworms) 吸虫纲 扁形动物门 Cestoda 绦虫纲

The Nematodes 线虫 There are many, many nematodes

2006 诺贝尔奖 : ＲＮＡ干扰机制

2002 年诺贝尔奖：程序性细胞死亡

C.Elegans

MorphologyMorphology

Cylindrical, non-segmented, bilaterally symmetrical and sexes separate

Pseudocele 原体腔( pseudocoelom)

The body wall: cuticle 角皮层 hypodermis 皮下层

longitudinal muscle 肌层

Holomyarian type( Whipworm)

Polymyarian type ( Ascarids)

Meromyarian type (Hookworm)

The arrangement of the somatic muscles

Digestive system

Mouth pharynx esophagus

intestine anus

咽管 食管

肠管 肛门

Reproductive system

male reproductive system

Testis seminal vesicle 睾丸 储精囊

vas deferens 输精管 ejaculatory duct 射精管

Most females usually have two ovaries ， oviducts and uterus..

ovary—oviduct —uterus.ovary—oviduct —uterus.. 卵巢 输卵管 子宫

vulva -vagina 阴门 阴道

nervous system

Consist of :

circumesophageal nerve ring 咽管神经环 and2 or 4 longitudinal nerve trunks 神经干

Excretory system

Excretory pore is anterior. 排泄孔

No flame cells are present.

life cycle

M1 M2 M3 M4 Egg L1 L2 L3 L4 Adult larva (male & female)

Kinds of life cycle in nematodes

Ascaris lumbricoides Trichuris trichiura Enterobius vermicularis Hookworms

Indirect life cycle: intermediate host is necessary

Trichinella spiralis Filaria

Direct life cycle: Intermediate host is not necessary

土源性线虫（肠道线虫）

生物源性线虫

Pathogenesis

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

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

What about Egg ？

INTESTINAL HELMINTHS

Ascaris lumbricoides (roundworm) 似蚓蛔线虫Trichuris trichiura (whipworm) 毛首鞭形线虫 Enterobius vermicularis (pinworm) 蠕形住肠线虫Ancylostoma duodenale and Necator americanus

(hookworms) 钩虫

2004 年第二次寄调

Ascaris lumbricoides (ascarids)

Adults live in intestine of human, cause Ascariasis ( 蛔虫病 ) ；Human is the only definitive host of this parasite.

>1 billion world wide

the infective rate in China 12.72%

Hookworms

Five species of hookworms:

Ancylostma duodenale 十二指肠钩口线虫

Necator americanus 美洲板口线虫Ancylostma ceylanicum 锡兰钩口线虫Ancylostma caninum 犬钩口线虫Ancylostma brazilience 巴西钩口线虫

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

Number of humans infected is estimated at 1.2 billion with 50,000 to 60,000 deaths each year.

国内： 6.12%

Enterobius vermicularis(Pinworm)

Almost anybody can

become infected with

this

parasite ， especially

children.

The worldwide infection is about 210 million

国内： 10.28%

Morphology

Morphology － Adult of Ascaris lumbricoides

the largest nematode parasites of humans

Creamy white or pinkish in color

elongate and cylindrical

Female: measuring 35cm long, posterior end is straight

Male: measuring 25cm long ， posterior end is curved .

Morphology － Adults of Ascaris lumbricoides

Three lips around

the mouth in

“ 品” type and

possess small teeth

Morphology － Adults of Ascaris lumbricoides

50 mm long with a slender anterior and a thicker posterior end The male is smaller and has a coiled posterior end

Morphology － Adults of Trichuris trichiura

Morphology － Adults of Enterobius vermicularis

Adults: pin-like, white, small worm

Female showing esophageal bulb & cephalic alae

Male with curved posterior end, Female has a long pointed end.

咽管球 头翼

Morphology － Adults of hookworms

Adult: Slender, pinkish or creamy-gray in color, about 10mm in length.

Females:9-13 mm long with egg-filled uterus Males:7-11 mm long, Posterior

end forms a Copulatory bursa ( 交合伞 )

Morphology － Adults of hookworms

Morphology of Ancylostoma duodenale

Buccal capsule contains 2 pairs of large ventral (anterior) teeth

Copulatory bursa is at posterior end and contains 2 thin spicules that separate distally.

口囊

交合伞

Morphology of Necator americanus

Buccal capsule contains a pair of ventral and dorsal cutting plates.

Copulatory bursa contains spicules that are fused distally.

shape “c”, 1cm± “s”, 1cm±

buccal capsule flat and oval-shape oval-shape two pairs one pair cutting plates

Copulatory bursa round oblate

spicule two, separated two, fused at their ends

A.duodenale N. americanus

Difference between A.duodenale and N. americanus

Morphology － larva of hookworms

rhabditiform Larva 杆状蚴 filariform larva : infective stage

Eggs are unembryonated when passed in the feces. Embryonation occurs in the soil.

Unembryonated egg in feces

broadly oval

yellowish to brown in color

Thick shell

ovum

protein coat

fertilized

Morphology － Eggs of Ascaris lumbricoides

unfertilized and fertilized egg

Decorticated egg(lost outer albuminous

coating)

Embryonated egg in soil

Morphology － Eggs of Ascaris lumbricoides

Morphology － Eggs of Trichuris trichiura

size: 50-54 µm by 22-23 µm,

smaller than Ascarids’

Shape ： a typical barrel

Color ： yellow-brown

unstained two polar plugs

Shell ： quite thick

Contains ： unembryonated

egg

Morphology － Eggs of Enterobius vermicularis

size: smaller than Ascarids’

Shape ： oval, flattened on one side

Color ： colorless

Shell ： quite thick

Contains ： an undeveloped larva

inside

Shape: oval-round Shell: thin with smooth

and colorless (transparent) eggshell

Size: 57-76 µm by 35-47 µm

Contains: clear space between the egg-shell and the ovum.

Usually 2 to 16 cells in feces

Morphology － Eggs of hookworms

Morphology － Eggs of hookworms

Life cycle

Life cycle of Ascaris lumbricoides

Adult egg infective egg larva

Ingested by man

migration

Life cycle

Migration of larva in the host:

Vessels of intestine liver heart lungs

trachea pharynx intestine(swallowed)

Life cycle of hookworm

Life Cycle

Adult egg rhabditiform filariform larva larva Swallowed pharynx trachea lung circulation

Penetrate skin

Life cycle of Enterobius vermicularis

Life cycle

ingested

Adult egg infective egg

(in lumen of cecum)

Pathogenesis

Pathogenesis of Ascaris lumbricoides

1) larvae: Ascaris Pneumonitis

Asthma

Larva in section of lung

Pathogenesis

2) Adults ： (1) Malnutrition

(2) Disorder of digestive system: main complaint--- abdominal pain

(3) Allergic responses

anorexia ( 食欲不振 ) nausea ( 恶心 )

vomiting ( 呕吐 ) diarrhea ( 腹泻 )

Complication 并发症

penetrate to bile ducts

penetrate to the pancreatic and the appendix

胆道蛔虫症

胰腺 阑尾

intestinal obstruction 肠梗阻

Ectopic parasitism 异位寄生

1. cause irritation( pruritus 搔痒 ) of the anal

region

Secondary bacterial infection in areas

scratched raw may occur.

2. vaginitis and rarely salpingitis in young girls.

阴道炎 输卵管炎

3. cause mental anguish

Pathogenesis of Enterobius vermicularis

Pathogenesis of hookworm

1. Local dermatitis (ground itch) 钩蚴性皮炎

2.Pulmonary (pneumonia-like) symptoms

(symptoms are not as severe as Ascaris migration)

3. Anemia

a. The worm sucks blood and the wound oozes blood

 A. duodenale takes 0.26 ml/day; N. americanus 0.03 ml/day

b. The worm usually changes its sucking site

c. Disfunction of intestine to absorb iron

gradually produce an iron-deficiency anemia

4. gastroenteric symptoms 胃肠道症状 Slight, intermittent abdominal pain

5. Aberration of appetite(geophagy 异嗜症 ) .

loss of normal appetite and desire to eat soil

or un-normal materials

6. Hookworm diseases of infant

7. eosinophilia

Laboratory Diagnosis

Laboratory Diagnosis

1. By identifying the eggs

1. direct fecal smear

2. brine-floatation method （饱和盐水浮聚法）

3. Scotch tape technique (cellophane tape impression) 透明胶纸黏贴法

4. Larval cultivation

( 钩蚴培养法 )

2. By identifying the adults

3. therapeutic test

Epidemiology

distribution

Basic conditions in parasitic epidemiology

Patients and infected persons

Souce of infection

Mode of transmission (Factors of prevalence)

For round worm

For hookworm

Via mouth

Warmer and poor sanitation

Inadequate disposal of feces

Using nightsoil as fertilizer

Via skin

Bare-foot walking

Others:Oral （ A. doudenale)PlacentaMother’s milkParatenic hosts

Susceptible population

“Hand-to-Mouth”Transmission

retroinfection through anus

inhalation of ova

For pinworm

Epidemiology

the reason for wide distribution of Ascaris l

1. simple life cycle

2. high reproductive capacity (240,000 eggs per day)

3. resistance of egg (due to presence of ascarosidal )

4. social customs and habits

Treatment Prevention and control

Treatment of patients and carriers,

Blockade of the route of transmission

Protection of the susceptible population

(personal prophylaxis)

Chemoprophylaxis, vaccines, other preventive

measures

Treatment Prevention and control

Treatment:

Mebendazole （甲苯哒唑） Albendazole （阿苯哒唑，肠虫清）

To prevent re-infection of E.v, treat the whole

family.

Others for hookworm diseases? 透热疗法 纠正贫血

Prevention and control:

hygienic control of food, feces

Good hygiene is the best preventive measure

Wash all bed clothes and bedding in hot water to

kill infective eggs of E.v.

avoidance of contact with infected fecal material

Others?

Dog and Cat Hookworms

HUMANS may serve as accidental hosts of these hookworms when the filariform larvae penetrate human skin

Creeping Eruption

匍形疹