Ascaris lumbricoides
Adults
Adult A. lumbricoides worm usually assume a creamy – white color with a tint of pink . Fine striations are visible on the cuticle . Ascaris adult worms are the largest known intestinal nematodes. The average adult male is small only seldom reaching 30 cm in length. The male is characteristically slender and possesses a prominent incurved tail. The adult female measures 22 to 35 cm in length and resembles a pencil lead in thickness.
Fertilized eggs
The fertilized A. lumbricoides egg is more rounded than the unfertilized version usually measuring 40 to 75 ?m . fertilization of the egg transforms the amorphous mass of protoplasm into an undeveloped unicelular embryo. A thick chitin shell is sandwiched in between the embryo and mammillated albuminous material (corticated). Both layers protect the embryo from the outside environment.
Unfertilized eggs
The typical oblong unfertilized A. lumbricoides egg characteristically measures 85 to 95 ?m by 38 to 45 ?m. A thin shell protects the inner amorphous mass of protoplasm . the egg is usually corticated .
Life cycle
The life cycle of A. lumbricoides is relatively complex compared with the parasites presented thus far. Infection begins following the ingestion of infected eggs that contain viable larvae. Once inside the small intestine, the larvae emerge from the eggs. The larvae then complete a liver lung migration by first entering the blood via penetration through the intestinal wall. the first “stop” on this journey is the liver . From there, the larvae continue the trip via the blood stream to the second “stop” the lung . Once inside the lung, the larvae burrow their way through the capillaries into the alveoli . Migration into the bronchioles then follows. From here , the larvae are transferred through coughing into the pharynx, where they are then swallowed and returned to the intestine.
Maturation of the larvae occurs, resulting in adult worms, which take up residence in the small intestine. The adults multiply and a number of the resulting undeveloped eggs (up to 250,000 per day) are passed in the feces .
Clincal symptoms
Ascariasis / Roundworm Infection :
Patients who develop symtomatic ascariasis may be infected with as few as a single worm . such a worm may produce tissue damage as it migrates through the host . a secondary bacterial infection may also occur following worm perforation out of the intestine.
Patients infected with many worms may exhibit vague abdominal pain, vomiting, fever, and distention . mature worms may entangle themselves into a mass that may ultimately obstruct the intestine, appendix, liver, or bile duct . such intestinal complications may result in death. In addition, discomfort from adult worms exiting the body through the anus, mouth, or nose may occur. Heavily infected children who do not practice good eating habits may develop protein malnutrition .
Laboratory diagnosis
The specimen of choice for the recovery of A. lumbricoides eggs is stool . adult worm may be recovered in several specimen types depending on the severity of infection , including the small intestine, gallbladder, liver and appendix. In addition, adult worms may be present in the stool, vomited up or removed from the external nares, where they may attempt to escape. An enzyme-linked immunosorbent assay (ELISA) is also available.