Nematode
The intestinal
nematodes
–
–
–
–
Ascaris
Hook worms
Pin worm
Whip worm
The blood- and tissue
dwelling nematodes
– The filaria
– Trichinella
Ascaris
蛔虫
Ascaris lumbricoides
似蚓蛔线虫
Introduction
• The first representative and the most
common intestinal parasite
• Cosmopolitan in distribution
• Rural > urban
• Children > adults
Morphology
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
Egg shell
Ovum
Albuminous layer
A. lumbricoides, fertilized egg (6050 micrometer)
A. lumbricoides, fertilized egg
A. lumbricoides unfertilized egg
The life cycle of A. lumbricoides
Living site
Adults in small
intestine
Migration
Larvae migrate
though the lungs
HOST
MAN
Diagnostic stage
Undeveloped
eggs in feces
Method of infection
Infective stage
Infective eggs are
ingested
Eggs embryonate in
soil by 2-3 wks
Symptomatology
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
Diagnosis
• Microscopic identification eggs in the
stool
a 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
• 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)
Treatment
• Albendazole
a single oral dose of 400 mg
• Mebenazole
100 mg orally twice daily for 3 days
Prevention
• 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 worms
钩虫
Ancylostoma duodenale
十二指肠钩口线虫
Necator americanus
美洲板口线虫
Pinworm
蛲虫
Enterobius vermicularis
蠕形住肠线虫
Whip worm
鞭虫
Trichuris trichiura
毛首鞭形线虫
Adult worms of Ancylostoma duodenale
Adult worms of Necator americanus
Morphology
• 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 americanus
Note : 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
Larger
Smaller
“C”
“S”
4 hooklets
2 plates
Spicules
Round
Tridigitate at
the terminus
Separated
Broader
Bidigitate at the
base
Fused at terminal
Mucron
Present
Absence
Size
Shape
Buccal
capsule
Bursa
Dorsal ray
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 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,
jejunum
蛲虫: colon
Gravid female adult deposits its eggs on the
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
mucosa, 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 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 Control
蛲虫
• Readily endemic in children concentrated
units
• 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)