NematodeNematode

The intestinal nematodes– Ascaris

– Hook worms

– Pin worm

– Whip worm

The blood- and tissue dwelling nematodes

– The filaria

– Trichinella

Ascaris蛔虫

Ascaris lumbricoidesAscaris lumbricoides似蚓蛔线虫似蚓蛔线虫

IntroductionIntroduction

• The first representative and the most

common intestinal parasite

• Cosmopolitan in distribution

• Rural > urban

• Children > adults

MorphologyMorphology

Adult

Looks like an earthworm

Female (20-35 cm); Male (12-30 cm)

3 lips which carry minute teeth

A pair of female and male worms of A. lumbricoides. Notice the vulvar waist(arrow)of the female worm and the coiled end of the male worm.

Ascaris female worm

A scanning electron micrograph of Ascaris showing the three prominent “lips”

Egg

• Fertilized egg

• Unfertilized egg

Albuminous layer

Egg shell

Ovum

A. lumbricoides, fertilized egg (6050 micrometer)

A. lumbricoides, fertilized egg

A. lumbricoides unfertilized egg 

The life cycle of A. lumbricoides

Living site

Adults in small intestine

Diagnostic stage

Undeveloped eggs in feces

Infective stageEggs embryonate in soil by 2-3 wks

Method of infection

Infective eggs are ingested

Migration

Larvae migrate though the lungs

HOSTHOST

MANMAN

SymptomatologySymptomatology

Larva

Pneumonitis

Asthma attacks

Loeffler’s syndrome

Adult• The presence of few worms may be

asymptomatic (85%)

• The most common symptoms are vague abdominal pain

• Large numbers of worms may cause malnutrition and present signs and symptoms of obstruction

• Migration of adult worms may cause signs

and symptoms of perforation, peritonitis,

appendicitis or extrahepatic biliary

obstruction.

A.lumbricoides in common bile duct

Cross section of a liver specimen contains many adult worms of A.lumbricoides obstructing the intrahepatic and extrahepatic bile ducts.

Ascarid chronic pancreatitis

A large mass of Ascaris lumbricoides that was passed from the intestinal tract.  The ruler at the bottom of the image is 4 cm (about 1.5 inches) in length.

An autopsy specimen shows intestinal obstruction by many adult worms of A.lumbricoides. Notice the markedly distended intestinal loop, the thin intestinal wall with hemorrhage and worms protruding from the perforated wound.

Peritonitis caused by intestinal perforation due to Ascaris

Resected bowel and the adult female from the peritoneal cavity

DiagnosisDiagnosis

• Microscopic identification eggs in the stoola direct wet mount examination of the specimen (200,000 eggs/female/day)

• Macroscopic identification of adults passed in stool or through the mouth or nose

Epidemiology Epidemiology

• Worldwide distribution, throughout the temperate and tropical areas

• 1,000,000,000 people in the world

• 40% population in Africa and Asia

• 600,000,000 in China (1992)

TreatmentTreatment

• Albendazolea single oral dose of 400 mg

• Mebenazole100 mg orally twice daily for 3 days

PreventionPrevention

• Avoid contacting soil that may be

contaminated with human feces

• Do not defecate outdoors

• Dispose of diapers properly

• Wash hands with soap and water before

handling food

• When traveling to areas where sanitation

and hygiene are poor, avoid water or food

that may be contaminated

• Wash, peel or cook all raw vegetables and

fruits before eating

Hook wormsHook worms钩虫钩虫

Ancylostoma duodenaleAncylostoma duodenale十二指肠钩口线虫十二指肠钩口线虫

Necator americanusNecator americanus美洲板口线虫美洲板口线虫

PinwormPinworm蛲虫蛲虫

Enterobius vermicularisEnterobius vermicularis蠕形住肠线虫蠕形住肠线虫

Whip wormWhip worm鞭虫鞭虫

Trichuris trichiuraTrichuris trichiura毛首鞭形线虫毛首鞭形线虫

Adult worms of Ancylostoma duodenale

Adult worms of Necator americanus

MorphologyMorphology

• Adult

– Cylindrical with the head bent sharply

backwards

– Males are smaller than the females and possess

a bursa at their posterior end

Scanning electron micrograph of the oral opening of Ancylostoma duodenale, another species of human hookworm.  Note the

presence of four cutting "teeth," two on each side.

Adult mouthpart of Necator americanusNote : The large buccal capsule is open dorsally with one pair

of cutting plate teeth.

Bursa of hookworms

Lift A. duodenale; Right N. americanus

A.d N.a

Size Larger Smaller

Shape “C” “S”

Buccal capsule

4 hooklets 2 plates

Bursa Round Broader

Dorsal ray Tridigitate at t

he terminusBidigitate at the b

ase

Spicules Separated Fused at terminal

Mucron Present Absence

Enterobius vermicularis adult female

0.8-1.3cm.in length , spindle-shaped with a long thin sharply tail. The greater part of the body is occupied by the uterus filled with eggs.

Trichuris trichiura adults. 

• Egg (indistinguishable between the 2

species)

– Median size (like the ascaris egg)

– Elliptical

– Transparent

– Thin shell

– 4-cell stage when discharge

Enterobius vermicularis egg. Note the thick shell and characteristic shape; approximate length = 55 µm.

Egg

< Ascaris egg

Non-symmetrical ellipse; D shaped

Transparent

Thick transparent shell

Tadpole-like embryo when discharged

Trichuris vulpis egg

Life CycleLife Cycle• Host -man

• No intermediate host

钩虫 : Egg Larva (free-living)

Larvae migrate from skin to the lungs

蛲虫 :Egg takes 6 hours to be infective stage

鞭虫 : Similar to Ascaris but no pulmonary migration . There are reservoir hosts.

Parasitic site: 蛔虫 : small intestinal 钩虫 : upper small intestine; Duodenum, jej

unum

蛲虫 : colon

Gravid female adult deposits its eggs on th

e anus and perianal skin.

鞭虫 : ileo-caecal region

Infection stage

蛔虫 : infective egg

钩虫 : infective larva

蛲虫 : infective egg ( Egg takes 6 hours to be infective stage)

infective mode: Anus-Hand-Mouth

Auto-infection/Cross-infection

鞭虫 : infective egg

Pathogenic stage: 蛔虫 : adult worm /larva

钩虫 :adult worm

Digestive disturbances /Allotriophagy

Microcytic hypochromic anemia

(sucking, oozing, discharging)

A.d. 0.15-0.4ml/d; N.a. 0.02-0.1ml/d

larva:Dermatitis ‘ground itch’

Pneumonitis and Bronchitis

Pathogenic stage: 蛲虫 :adult worm Anal itching (migration of gravid females)

Ectopic infection

Digestive disturbances

鞭虫 :adult worm Digestive disturbances Anemia

Trichuris trichiura in the large intestine.  Many worms are present, each with its anterior end embedded in the intestinal mucos

a, resulting in the erythema. 

Etiologic dignosis: 蛔虫 :fecal direct smear

钩虫 :Brine floatation

Larva cultivation

Egg counting(to estimate infection intensity)

蛲虫 : Collect eggs from perianal region by anal swab on the cellophane tape. Search adult female in the perianal region when the child is sleeping.

鞭虫 : Brine floatation

Prevention and ControlPrevention and Control钩虫 :Distribution

Cosmopolitan

0.4 billion humans are infected in China• Natural factors

– Soil contamination– Night soil as fertilizer– Suitable climate dry-land vegetable- raising

& mine

Prevention and ControlPrevention and Control蛲虫• Readily endemic in children concentrated u

nits

• Should put the prevention in first

• Mebendazole(100mg repeated after 2 weeks)

鞭虫 Principles same as for ascaris

Drug: Albendazole 400mg/d

阿苯达唑 / 丙硫咪唑 / 肠虫清 Mebendazole

100mg/ 次 2 次 /d 连服 3 天 (600mg repeated after 2 weeks)