Disease. Ascariasis is an infection of the small intestine caused by Ascaris lumbricoides (the largest nematode or roundworm). Ascariasis is most prevalent in children of tropical and developing countries. Usually asymptomatic. Symptomatic ascariasis may manifest as growth retardation, pneumonitis, intestinal obstruction, or hepatobiliary and pancreatic injury.
Life cycle. Adult worms reside in the upper part of the small intestine, where they survive on predigested food. The worms make themselves into an S-shape and press against the epithelium of the intestine while moving against the peristalsis to keep themselves in the small intestine. The female worm lays eggs, and she can produce up to 200,000 eggs per day. These eggs are fertilized but non-embryonated, and the eggs are passed out with feces. The fertilized eggs develop through embryonation in feces deposited in the soil. The process of embryonation takes 2-4 weeks. The eggs can survive many months before embryonation starts, but they need a moist aerobic environment to develop. The eggs are only infective once they are embryonated and have larvae in them. Once embryonated, the infective egg must be swallowed to complete the life cycle of A. lumbricoides. Bile salts and alkaline enteric juice of the small intestine stimulate the release of the larvae from the eggs. These second-stage larvae then travel from the small intestine to the liver. Then the larvae migrate to the heart via pulmonary circulation. The larvae are now third-stage larvae in the alveolar capillaries, and they enter the alveolar spaces. Afterward, they migrate to the bronchi into the trachea and then to the epiglottis.
Epidemiology and Risk Factors. The most common human worm infection, infection occurs worldwide. Tropical and subtropical areas where sanitation and hygiene are poor. About 1.5 billion persons were infected with Ascaris in 2002. Children > than adults: most common age group 3-8 years. Poor nutritional status: more serious infectionAscariasis may exist as a zoonotic infection associated with pigs and use of hog manure. People who raise pigs or use raw pig manure as fertilizer may be at risk for infection with Ascaris suum. Contact with pigs should be investigated as a potential cause upon diagnosis of ascariasis. In most endemic areas, it is most likely transmitted from person to person. Transmission of Ascaris lumbricoides infection to others in a community setting can be prevented by not defecating outdoors and effective sewage disposal systems.
Clinical features. The clinical features are cough, dyspnea, asthma, and chest pain during initial lung migration. Abdominal pain, distension, colic, nausea, anorexia, intermittent diarrhea with partial or complete intestinal obstruction by adult worms. Jaundice, nausea, vomiting, fever, and severe/radiating abdominal pain may suggest cholangitis, pancreatitis, or appendicitis.
Diagnosis. The diagnosis available with stool examination: discloses large brown 60 X 50 mm trilayered eggs. Fertilized eggs have an uneven mucopolysaccharide coat on their outer surfaces. Larvae may be observed in microscopic wet preparations of sputum during the pulmonary migration phase. Eosinophilia during the tissue migration phase of the infection.
Treatment. Anthelminthic medications (drugs that rid the body of parasitic worms), such as albendazole and mebendazole, are the drugs of choice for treatment of Ascaris infections, regardless of the species of worm. Infections are generally treated for 1-3 days. The drugs are effective and appear to have few side effects.
References:
Adachi K. Ascariasis. Available from: https://web.stanford.edu/group/parasites/ParaSites2002/ascariasis/
Centers for Disease Control and Prevention. Parasites – Ascariasis.[Updated: February 15, 2018]. Available from: https://www.cdc.gov/parasites/ascariasis/index.html
Haburchak D.R. Ascariasis. Medical College of Goergia. 2002. Available from: (https://emedicine.medscape.com/article/212510-overview)
