Ascaris lumbricoides (Roundworm) Eggs: Morphology, Characteristics and Identification

The Roundworm, Ascaris lumbricoides is the largest nematode parasite in human intestine. Disease caused by A. lumbricoides is called Ascariasis. Laboratory diagnosis of ascariasis can be made by demonstration of parasite (eggs, larvae or adult worm) or some serological methods on clinical specimens. Definitive diagnosis of ascariasis is made by the demonstration of eggs in feces.

A gravid female roundworm can lay upto 2,50,000 eggs per day. This accounts for about three eggs per mg of feces. At this concentration, the eggs can be readily seen by the microscopic examination of saline emulsion of feces. Two types of eggs are liberated from the female worm of Ascaris lumbricoides:

• Fertilized eggs
• Unfertilized eggs

Feces sample may show both fertilized and unfertilized eggs, or either type alone.

Fertilized Eggs

The fertilized eggs are laid by females after inseminated by mating with a male. These are embryonated and develop into the infective eggs.

Morphology and Features

Shape	Round to oval.
Size	50-70um x 40-50um
Covering	Surrounded by a thick smooth transleucent shell consisting of three layers: -The outer coarsely mamillated albuminoid coat -A thick transparent middle layer -Inner lipoidal vitelline membraneSome eggs are found in feces without the outer mamillated albuminous coat. These are called decorticated eggs.
Bile Staining	Bile stained, golden brown in saline mount.
Floatation	Floats in saturated salt solution.
Ovum	Contains a large unsegmented ovum of granular mass with clear space at both the end.

Unfertilized Eggs

The unfertilized eggs are laid by uninseminated female. Thes are non-embryonated and cannot become infective.

Morphology and Features

Shape Round to oval.

Size	90um x 45um
Covering	Albuminous coat is thin, distorted and scanty.
Bile Staining	Bile stained, golden brown in saline mount.
Floatation	Doesn’t float in saturated salt solution.
Ovum	Contains an unsegmented small atrophied ovum with a mass of disorganized highly refractile granules.