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 60×45 µ m  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 intestine--- blood stream --- right side of the heart --- lung -- - respiratory tree --- coughed up and swallowed --- small intestine  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 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 mm in length, and the male about mm

Morphology: eggs ☆ barrel-shaped or fusiform with bipolar prominences (plugs) ☆ measures by µ m ☆ 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 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: Cotton swab Cotton swab Cellophane tape Cellophane 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