Experiment 1 Nematodes

Four species of Nematodes： Ascaris lumbricoides（蛔虫） Hookworm （钩虫） Trichuris trichiura (鞭虫 ) Enterobius vermicularis(蛲虫）

Ascaris lumbricoides (似蚓蛔线虫)

Morphology of adults The adults are cylindrical in shape, creamy-white or pinkish in color. The female averages 20-35cm in length. The male is smaller, averaging 15-31cm in length and distinctly more slender than the female

Adult worm of A. lumbricoides

The typical curled tail with a pair sickle like copulatory spine readily distinguishes males.

The lips of Ascaris lumbricoides On the tip of the head there are three lips, arranged as a Chinese word “ 品 ”. mouth lip The lips of Ascaris lumbricoides

The lips of Ascaris lumbricoides Scanning electron microscope of the lips of Ascaris lumbricoides

They have a complete digestive tract. Reproductive organs are tubular They have a complete digestive tract. Reproductive organs are tubular. 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.

female male

There are two kind of the eggs There are two kind of the eggs. They are fertilized eggs and unfertilized eggs. We usually describe an egg in 5 aspects: size, color, shape, shell and content. Egg fertilized eggs unfertilized eggs.

Fertilized eggs: broad oval in shape, brown in color, an average size 60× 45µm. The shell is thicker and consists of ascaroside, chitinous layer, fertilizing membrane and mammillated protein coat outside of egg shell The content is a fertilized ovum. There is a new-moon shaped clear space at the each end inside the shell.

Freshly Passed Ascaris Eggs From feces The eggs may appear from light to dark brown in color.

Decorticated egg: Normal fertile eggs may lack the mammillated layer and are referred as decorticated eggs.

larva

Unfertilized egg Longer and slender than a fertilized egg. The chitinous layer and protein coat are thinner. The content is made of many refractable granules various in size.

Unfertilized and Fertilized Eggs

Diagnosis The symptoms and signs are for reference only. The confirmative diagnosis depends on the recovery and identification of the worm or its egg.

1. Ascaris pneumonitis: Examination of sputum for Ascaris larvae is sometimes successful. 2. Intestinal ascariasis: Feces are examined for the ascaris eggs. (1) Direct fecal film: It is simple and effective. The eggs are easily found using this way due to a large number of the female oviposition, approximately 240,000 eggs per worm per day. So this method is the first choice.

(2) Brine-floatation method: (3) Recovery of adult worms: When adults or adolescents are found in feces or vomit and tissues and organs from the human infected with ascarids , the diagnosis may be defined.

Ancylostoma duodenale and Necator americanus Adult Egg A.duodenale likes the letter “C” N.americanus likes the letter “S” A.duodenale is larger than N.americanus

Morphology Adults: ＊ Cylindrical with the head bent sharply backwards, look like a hook, about 1cm. ＊ They are white or light pinkish when living. Female is slightly larger than male. ＊The male’s posterior end is expanded to form a copulatory bursa. 22

The Morphological Differences between Two species of Hookworms A. duodenale N. americanus ______________________________________________________ Size larger smaller Shape single curve, looks like C double curves, looks like S Mouth 2 pairs of ventral teeth 1pair of ventral cutting plates ____________________________________________________________ Copulatory circle in shape oval in shape Bursa (a top view) (a top view) Copulatory 1pair with separate 1pair of which unite to form spicule endings a terminal hooklet _______________________________________________________ caudal spine present no vulva position post-equatorial pre-equatorial

Ancylostoma duodenale Note the presence of two pairs of “curved teeth” on the ventral wall , two on each side. Scanning electron micrograph of the oral opening of Ancylostoma duodenale.

Necator americanus This species contains a pair of semilunar cutting plates on the ventral wall.  Scanning electron micrograph of the oral opening of Necator americanus.

Bursa & dorsal ray rounded, dorsal ray tripartite ventral ray lateral ray dorsal ray rounded, dorsal ray tripartite tridigitate at the terminus Broader than long , dorsal ray small,bipartite bidigitate at the base A. duodenale N. americanus

dorsal ray dorsal ray of A. duodenale dorsal ray of N. americanus

Hookworm Eggs 60×40 µm in size, oval in shape, shell is thin and colorless. content is 2,4 or 8 cells. a clear space is always present between the cells and the egg shell. ×400. Enlarged Morphologically it is not possible to differentiate eggs between A. duodenale and N. americanus..

Adults in intestinal mucosa Intestinal phase: worms attach to the mucosa and feed on blood.

diagnosis Methods: 1. saturated brine flotation technique 2. direct fecal smear

Trichuris trichiura 毛首鞭形线虫 Adult Egg

Morphology Adult: The worm looks like a buggy whip, the anterior 3/5 is slender and the posterior 2/5 is thick. It is pinkish gray in color. The female worm is 3-5 cm in length and has a long slender esophageal region. . Both male and female have a single reproductive tubule

Egg: It is barrel or spindle in shape and 50 x 20µm in size. It is brownish and double shelled. has a transparent polar plug at either ends. The content of the egg is an undeveloped cell. Eggs of T. trichiura under the high power

Egg

adult worms deep into the caecal submucosa

diagnosis Discover the eggs in feces by floatation method or direct fecal smear.

Enterobius vermicularis (蠕形住肠线虫)

Morphology Adults: Look like a pin and are white in color. The female worm measures about 8-13 mm , have a pointed tail. The male adult is only 2-5mm and the tail curved. They die right after mating, thus males are rarely seen. At the anterior end , flanked on each side by cuticular extensions called “ cephalic alae”. The esophagus is slender, terminating in a prominent posterior bulb , which is called “esophageal bulb”. The cephalic alae and esophageal bulb are important in identification of the species.

Enterobius vermicularis male female Enterobius vermicularis

adult The cephalic alae are clearly seen at the anterior end. The cuticle and alae are transversely striated. The esophageal bulb are also visible.

Anterior part of E. vermicularis. Cephalic alae esophageal bulb Anterior part of E. vermicularis.

Scanning electron micrograph of anterior part of E. vermicularis. ×2000.

egg 50 to 60 µm by 25 µm, colorless and transparent, thick shell, flattened on one side content is an immature larva.

The egg of E. vermicularis

Diagnosis Diagnosis depends on recovery of the characteristic eggs. The eggs and the female adults can be removed from the folds of the skin in the perianal regions by the use of the cellophane tape method. The examination should be made in the morning, before the patient has washed or defecated.

Manipulation Ascaris lumbricoides ： adult, the lips, copulatory spines of male ，the fertilized and unfertilized ova Hookworm: adult, Egg ，adults in intestinal mucosa. Trichuris trichiura: adult, Egg, adult worms deeply into the caecal submucosa Enterobius vermicularis: adult, egg

Exercise Draw the egg of these four nematodes. Mark the structure of the eggs. Where can you find the eggs?