Morphology of Soil Transmitted Helminths

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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).

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...
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