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Soil Transmitted Helminths Essay

I. ROUNDWORMS (ASCARIS LUMBRICOIDES)
A.Morphology

1. Eggs
The fertilized eggs are broadly oval, measuring 45 to 75 µm long by 35 to 50 µm wide. The outer covering is an albuminoid coat, usually stained a golden brown by bile as seen in the fresh stool. The outer coat is coarsely mammillated and lies directly on top of a thick smooth shell, which is usually not easily distinguished. Some eggs will be seen to have lost the outer albuminoid coat and in these, the thick yellowish inner shell is obvious. It is thicker than the shell of hookworm egg, which these decorticated Ascaris eggs otherwise resemble. The infertile eggs are longer and narrower than the fertile ones. They may measure about 90 by 40 µm.

Both the inner shell and outer albuminoid coat may be thin and if the latter is absent and the inner shell very thin, they may resemble Trichostrongylus eggs (Markell, Voge and John, 1992). The adult male of A. lumbricoides is 15 to 31 cm long and 2 to 4 mm at greatest width. The posterior end is curved ventrally, and the tail is bluntly pointed. Spicules are simple, nearly equal, and measure 2.0 to 3.5 mm long. No gubernnaculum is present. The adult female of A. lumbricoides is larger measuring 20 to 49 cm long and 3 to 6 mm wide. The vulva is about one-third the body length from the anterior end. The ovaries are extensive, and the uteri may contain up to 27 million eggs at a time with 200,000 being laid per day (Roberts and Janovy, 2005).

WHIPWORM (TRICHURIS TRICHIURA)

A.Morphology
1. Egg
The average barrel-shaped T. trichiura egg (Figure 4) measures 50 to 55 µm by 25 µm. The undeveloped unicellular embryo is surrounded by a smooth shell that retains a yellow-brown color from its contact with host bile. A prominent hyaline polar plug is visible at each end.

2. Adult
The adult male of T. Trichiura (Figure 4) are 30-45 mm long while the female of T. trichiura (Figure 4) are slightly larger, measuring 35 to 50 mm. The mouth is a simple opening, lacking lips. The buccal cavity is tiny and is provided with a minute spear. The esophagus is very long, occupying about two-thirds of the body length and consists of a thin-walled tube surrounded by large, unicellular glands, the stichocytes. The entire structure often is referred to as the stichosome. The anterior end of esophagus is somewhat muscular and lacks stichocyte. Both sexes have a single gonad, and the anus is near the tip of the tail. Male have a single spicule that is surrounded by a spiny spicule sheath. The ejaculatory duct joins the intestine anterior to the cloaca. In the female the vulva is near the junction of the esophagus and the intestine. The uterus contains many unembryonated, lemon-shape eggs, each with a prominent opercular plug at each end (Roberts and Janovy, 2005).

HOOKWORMS (ANCYLOSTOMA DUODENALE AND NECATOR AMERICANUS)

A.Morphology
1. Egg
Eggs of hookworms (Figure 6) recovered in freshly passed stool may be unsegmented or show a visible embryonic cleavage, usually at the two-, four-, or eight cell stage. However, eggs in stool samples that have been kept at room temperature (particularly under warm conditions) over time may reveal a developing larva. A thin, smooth, colorless shell provides protection for the developing worm. Because the size ranges of these two organisms are so close and the other characteristics are identical, recovered eggs are considered as indistinguishable, differing only slightly in size: N. americanus 60 to 75 µm and A. duodenale 55 to 60 µm. the width of both organisms ranges from 35 to 40 µm. (Zelbia, 1997) 2. Adult

Adult hookworms (Figure 7) are small cylindrical, fusiform, grayish white nematodes. The A. duodenale is larger than the N. americanus. The worm has a relatively thick cuticle. There are single male paired female reproductive organs. The posterior end of the male has a broad, translucent, membranous caudal bursa with riblike rays, which is used for attachment to the female during copulation. The chief morphologic differences in the species are in the shape, buccal capsule, and male bursa. The vulva is located anterior to the middle of the body in N. americanus and posterior in A. duodenale. In the buccal capsule N. americanus has a conspicuous dorsal pair of semilunar cutting pates, a concave dorsal median tooth, and a deep pair of triangular sub ventral lancets. A. duodenale has two ventral pairs of teeth (Neva and Brown, 1994).


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