Nematode( 线虫 ). Round Worms Introduction Among the commonest of all parasites and responsible...
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Transcript of Nematode( 线虫 ). Round Worms Introduction Among the commonest of all parasites and responsible...
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
female reproductive system
male 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 is
intermediated by the arthropod--- (filarial worm)
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
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
Morphology
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
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
Morphology
Life Cycle
Site of inhabitation: small intestine Infective stage: embryonated eggs Route of infection: by mouth Blood-lung migration: intestine--- blood intestine--- blood
stream --- right side of the heart --- lung stream --- right side of the heart --- lung --- respiratory tree --- coughed up and --- respiratory tree --- coughed up and swallowed --- small intestineswallowed --- 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
Life Cycle
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
Pathogenesis
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
Diagnosis
Worldwide distribution, very common in China, especially in the countryside.
Infection rate:
rural >urban;
children > adults
Epidemiology
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
Treatment to ascariasis: Mebendazole, Albendazole are effective
Sanitary disposal of feces. Hygienic habits such as cleaning of
hands before meals. Health education.
Prevention
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 30-45 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
Epidemiology1. 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
shell female
egg
male
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:Anal swab method:
Cotton swabCotton swab
Cellophane tapeCellophane tape
Epidemiology
Endemic in children concentrated units. There is no differences on the basis of sex, race, or socio-economic class.
Infection rate:
urban > rural;
children > adults
Principles of Control
1. Chemotherapy
2. Personal Sanitation