Transcript Fertilized egg

Nematode(线虫)
Round Worms
Introduction
Among the commonest of all parasites and
responsible for diseases of major importance
in humans
 Non-segmented roundworms belonging to the
Phylum Nemathelminthes, Class Nematoda
 The sexes are usually separate (Dioecious),
the male which is smaller than the female
commonly has a curved posterior end

Morphology
Cylindrical and slender
 Bilaterally symmetrical
 Sex-differentiated
 Celomic cavity: protocoele
 The supporting body wall consists of cuticle layer,
syncytial layer (subcutical layer) and longitudinal
muscular layer
 The alimentary tract is a simple tube extending
from the mouth to the anus

Morphology


No circulatory system
The reproductive system is in tubular
form with dioecious (sex-differentiation):
 The
male reproductive organs are
situated in the posterior third of the body
as a single coiled tube, the various parts
of which are differentiated as testis, vas
deferens, seminal vesicle, and ejaculatory
duct, also cloaca and spicule
 The female reproductive system may be
either a single or a bifurcated tube,
differentiated into ovary, oviduct, seminal
receptacle, uterus, ovejector and vagina
Digestive system
male reproductive system
female reproductive system
Physiology

The methods of obtaining food may be classified as
 Sucking with ingestion of blood (Ancylostoma)
 Ingestion of lysed tissues and blood (Trichuris)
 Feeding on the intestinal contents (Ascaris)
 Ingestion of nourishment from the body fluids (filarial worms)


Metabolism: mainly aerobic metabolism, and most
species need free-living periods for larvae, which are
capable of withstanding a wide range of environmental
condition
During larval development, nematodes pass through
several molts or ecdysis, both inside and outside the
host
Life cycle

Geo-helminths
 Only one host: the larvae pass from host to host
directly or after a free-living existence
 Transmission to a new host depends upon
 the ingestion of the mature infectious eggs with
larvae (Ascaris, Pinworm)
 the penetration of the skin or mucous
membranes by the larvae (Hookworm)

Bio-helminths
 Have an intermediate host
 Transmission to a new
definitive host
intermediated by the arthropod--- (filarial worm)
is
Common medical nematodes species

Intestinal lumen residing nematodes:
 Ascaris, Hookworm, Whip worm, Pinworm----the
adult parasite inhabit in human intestinal tract

Blood and tissue residing nematodes:
 Filaria, Thichinella----the location of the adult
parasite is blood or tissue
Ascaris Lumbricoides
(似蚓蛔线虫,蛔虫)
General Introduction

Common saying “round worm of man”

The largest of the intestinal nematodes
parasitizing humans


The most common worm found in human
It is worldwide in distribution and most
prevalent through out the tropics, sub-tropics
and more prevalent in the countryside than in
the city

Morphology
Adult:
 Cylindrical in shape
 Creamy-white or pinkish in color
 The female averages 20-35cm in length, the largest
49cm
 The male is smaller, averaging 15-31cm in length,
has a typical curled tail with a pair sickle like
copulatory spines
 On the tip of the head there are three lips, arranged
as a Chinese word “ 品 ”
 Male has a single reproductive tubule
 The female has two reproductive tubules and the
vulva is ventrally located at the posterior part of the
anterior 1/3 of the body
Adult worm of A. lumbricoides
The lips of A. lumbricoides
The three lips are
seen at the anterior
end. The margin of
each lip is lined with
minute teeth which are
not visible at this
magnification
Morphology
Egg
 There are three kinds of the eggs
 fertilized eggs
 unfertilized eggs
 decorticated eggs
 We
usually describe an egg in 5 aspects
 size, color, shape, shell and content
Morphology

Fertilized egg:
 an average size 60×45µm
 broad oval in shape
 brown in color
 The shell is thick
 Albuminous coat is thick and stained brown by bile
 The content is a fertilized ovum
 There is a new-moon(crescent) shaped clear space at
each end inside the shell
Morphology

Unfertilized egg
Longer and slender than fertilized egg
 The shell and albuminous coat are thinner
than those of the fertilized egg
 The content is made of many refractable
granules various in size


Decorticated egg:
 Both
fertilized and unfertilized eggs
sometimes
may
lack
their
outer
albuminous coats and are colorless
Life Cycle
Life Cycle
 Site
of inhabitation: small intestine
 Infective stage: embryonated eggs
 Route of infection: by mouth
 Blood-lung migration: intestine--- blood
stream --- right side of the heart --- lung -- respiratory tree --- coughed up and
swallowed --- small intestine
Life Cycle
 No
intermediate and reservoir hosts
 The
time from the ingestion of
embryonated eggs to oviposition by the
females is about 60-75 days
 Life span of the adult: about 1 year
 Female
may produce approximately
240,000 eggs per day, which are passed
in feces
Pathogenesis
1.
The blood-lung migration phase of the
larvae: During the migration through the
lungs, the larvae may cause a pneumonia
(temporary).
 The symptoms of the pneumonia are low
fever, cough, blood-tinged sputum, asthma
 The clinical manifestation is also called
Loeffler’s syndrome
Pathogenesis
2. The intestinal phase of the adults
•
No symptoms to vague abdominal pains or
intermittent colic, especially in children
•
A heavy worm burden can result in malnutrition
•
Wandering adults may block the appendical
lumen or the common bile duct and even
perforate the intestinal wall which cause
complications of ascariasis:
•
•
•
•
•
intestinal obstruction
Appendicitis
biliary ascariasis (the most common one)
perforation of the intestine
cholecystitis, pancreatitis and peritonitis
Diagnosis
 The
symptoms and signs are for
reference only
 Intestinal
ascariasis: feces are
examined for the ascaris eggs
 Direct fecal film: it is simple and effective and
is the first choice
 brine-floatation method:
 recovery of adult worms: when adults or
adolescents are found in feces or vomit and
tissues
 Ascaris
pneumonitis: examination of
sputum
for
Ascaris
larvae
is
sometimes
Epidemiology

Worldwide distribution, very common in
China, especially in the countryside.
Infection rate:
rural >urban;
children > adults
 Factors
favoring the spread of the
transmission:
Simple life cycle
Enormous egg production ( 240,000 eggs/ day/ female )
Eggs are highly resistant to ordinary disinfectants
( due to the ascroside) which may remain viable for
several years
Social customs and living habits.
Disposal of feces is unsuitable
Prevention
 Treatment
to ascariasis: Mebendazole,
Albendazole are effective
 Sanitary disposal of feces.
 Hygienic habits such as cleaning of
hands before meals.
 Health education.
Trichuris trichiura (毛首鞭形线虫)
(whipworm,鞭虫)
General Introductions




A common nematode residing in human
colon
Human infection with whipworm once be
identified in coprolites of prehistoric man
Worldwide distributed in the same areas
where the Ascaris are found
Trichuriasis are usually not serious
clinically, but overwhelming infections
leading to death have been reported in
children
Morphology: adults
The adult female
measures about
35-50 mm in
length, and the
male about 3045 mm
Morphology: eggs
☆ barrel-shaped or fusiform with
bipolar prominences (plugs)
☆ measures 50-55 by 22-24 µm
☆ brown, smooth shell
☆ contains a single-cell ovum
Life cycle



No intermediate host
Infected through
fecal-oral route by
the embryonated egg
Ileocecal portion is
the most favorite site
of residing
Pathogenesis


Symptoms are determined largely by the
worm burden: less than 10 worms are
asymptomatic
Only heavily infected patients develop
clinical disease:

Chronic diarrhea, characterized by mucous
stools, and associated with tenesmus(里急后重)
 If the diarrhea is protracted, the patient may
develop rectal prolapse, more likely to occur in
small children
 Many individuals infected with whipworm tend to
be malnourished and anemic
Pathogenesis
prolapsed rectum
whipworms are often seen
attached to the rectal tissue
Laboratory Diagnosis
"Fecal direct smear " or
"sedimentation" are the methods of
choice for etiological diagnosis
Epidemiology
1. The infection is most common in tropical
areas where prevalence as high as 80%
has been documented
2. Commonly coexisting with Ascaris
infections
Principles of Control
Chemotherapy

Albendazole (400 mg per day for 3 days)
 Mebendazole (100 mg per dose, twice a day for 2
days)
Proper
disposal of feces is the primary means of
prevention

In areas of the world where untreated human feces
are used to fertilize crops, control of this infection is
impossible
Hygeian
education
Enterobius vermicularis (蠕形住肠线虫)
(Pinworm,蛲虫)
Introduction
1. A colon residing nematode of smaller
size.
2. One of the most widely prevalent
parasitic nematodes of human being.
3. Affecting mainly children below the
age of 12 years. No host other than
man.
Morphology
Adult :Small nematodes of
8~13mm in length by
0.3~0.6 mm in diameter,
with the spindly shape
 Egg : smaller than that of
ascaris, asymmetrical,
with a thin and colorless
female
shell

male
egg
anterior end of adult
Life Cycle
1. Adults inhabit in the cecum.
Female lay eggs in the perianal
region of the host.
2. No intermediate host, the egg
takes around 6 hours to be
matured and becomes the
infective stage.
3. Mode of infection may be
auto-infection or
cross-infection.
Pathogenesis
1.The migratory phase of the pinworm is restricted to the
gastrointestinal tract and thus the host does not experience
any systemic reactions.
2. Perianal itching may be complicated. Heavy infections in children
may also produce such symptoms as sleeplessness, weight
loss, hyperactivity, grinding of teeth, abdominal pain, and
vomiting.
3. Ectopic parasitism may happen, which can cause uro-genital
inflammations or even the pelvic cavity
be involved occasionally.
Laboratory Diagnosis
Anal swab method:
Cotton swab
Cellophane tape
Epidemiology
Endemic in children concentrated units. There is no
differences on the basis of sex, race, or socioeconomic class.
Infection rate:
urban > rural;
children > adults
Principles of Control
1.
2.
Chemotherapy
Personal Sanitation