Ascaris Lumbricoides Identification

Ascaris lumbricoides, or the large intestinal roundworm, is the largest and most common intestinal roundworm. Unsanitary conditions increase the risk of infection. People typically get infected through ingestion of the infective eggs. Laboratory diagnosis includes several techniques for identification of the microscopic eggs or the adult Ascaris.

The adult worm

• The adult Ascaris lumbricoides can be identified macroscopically by visual examination. They occasionally exit the body through the nose or the anus. The worm is creamy to pinkish-white in color, cylindrical, and tapered at both ends. The males grow to a length of 15 to 30 cm, while the female can grow up to 35 cm.

Ascaris eggs

• Finding the eggs in feces is the usual way to identify infection in a person. The eggs cannot be seen with the naked eye; therefore, the use of a microscope is required. The Ascaris eggs will show different appearances based on whether the egg is fertilized or unfertilized and whether there is the presence or absence of a mamillated coat. The size of the eggs microscopically range from 30 um to 90 um in length.

Direct Wet Mount

• The method of identification is prepared using an applicator stick and adding a small amount of feces to a drop of saline on a microscope slide. A cover slip is applied to the mixture so it spreads out thinly. The slide is examined using the 10x power objective to look for characteristic eggs.

Sedimentation method

• This fecal-concentration technique increases the possibility of detecting eggs when few are present in feces. The Formalin-Ethyl Acetate method is a sedimentation method that concentrates parasites in a large amount of feces into about 2 g of sediment. The sediment is then placed on a microscope slide and a cover slip is added. The slide is examined microscopically for eggs.

Flotation method

• The flotation method for concentrating the parasite eggs uses liquids with a higher specific gravity than that of the eggs so the eggs float to the surface. The concentrating solution, typically zinc sulfate, should have a specific gravity of 1.18. The one drawback of this method is large, unfertilized Ascaris eggs may be too heavy and will not float.