Ascariasis is the disease caused by Ascaris lumbricoides (A lumbricoides). Its incidence is concentrated in tropical and subtropical areas with poor sanitation.
Ascaris species are very large (adult females: 20 to 35 cm; adult males: 15 to 30 cm) nematodes (roundworms) that strive in the human intestine.
A lumbricoides is the primary species involved in human infections globally, but Ascaris suum in pigs may infect humans.
- Ascaris parasites live in the intestine.
- Ascaris eggs are passed in the feces of infected people.
- If an infected person defecates outside (near bushes, in a garden, or a field) or if the feces of an infected person are used as fertilizer, eggs are deposited on the soil.
- These eggs grow into adult parasites that can infect others.
Humans are infected with A lumbricoides when they ingest its eggs, often through food contaminated with human feces or when they inhale the soil that contains the eggs. Infection can occur when hands or fingers with contaminated dirt are put in the mouth.
Larvae lodge in the alveolar capillaries penetrates the alveolar walls and ascend the bronchial tree into the oropharynx. They are swallowed and return to the small bowel, where they develop into adult worms.
What is ascariasis?
Ascariasis is the most prevalent intestinal helminth infection in the world.
Current estimates suggest that about 500 million people are infected worldwide, and ascariasis contributes to malnutrition in areas with poor sanitation and where human feces are used as fertilizer.
Prevalence is highest in children aged 2 to 10 years and decreases in older age groups.
The life cycle of the worm
The entire lifecycle from egg ingestion to egg deposits takes about two or three months. Ascariasis worms can live inside the body for one to two years.
- Ingestion: The tiny ascariasis eggs become infective when in contact with the soil. People can accidentally ingest contaminated soil through hand-to-mouth contact or by eating uncooked fruits or vegetables that have been grown in contaminated soil.
- Migration: Larvae hatch from the eggs in the small intestine and penetrate the intestinal wall to travel to the heart and lungs via the bloodstream or lymphatic system. After maturing for about 10 to 14 days in the lungs, the larvae break into the airway and travel up the throat, where they are coughed up and swallowed.
- Maturation: In the intestines, the parasites grow into male or female worms. Female worms grow more than 15 inches (40 cm) long, and male worms are generally smaller.
- Reproduction: Each female worm can produce 200,000 eggs a day after mating with a male worm, and the eggs leave the body through feces. The fertilized eggs must remain in the soil for at least two to four weeks before they become infective.
What are the symptoms of ascariasis?
Later symptoms are gastrointestinal, including:
- Abdominal pain or discomfort due to obstruction of gastrointestinal lumina (intestines or biliary or pancreatic ducts) by adult worms
- Bloody stools
- Decreased appetite
People with many worms in the intestine might experience:
Chronically infected or heavy infections can block the intestines and slow growth in children.
A high worm burden may lead to intestinal obstruction and potential perforation. Migrating adult worms may cause symptomatic occlusion of the biliary tract, appendicitis, or nasopharyngeal expulsion, particularly in infections involving a single female worm.
How is ascariasis diagnosed?
Diagnosis is usually confirmed by:
- Microscopic examination of stools
- Identification of eggs or adult worms in stool or emerging from the nose, mouth, or rectum
- Occasionally, larvae can be found in sputum during the pulmonary phase
- Adult worms could be identified in radiographic studies of the gastrointestinal tract
How is ascariasis treated?
Ascariasis is treated by oral anthelmintic medications (drugs that remove parasitic worms from the body), such as:
- Albendazole: 400 mg, one time orally.
- Mebendazole: 100 mg, orally two times a day for three days or 500 mg one time orally.
- Ivermectin: 150 to 200 mcg/kg, one time orally.
Obstructive complications could be effectively treated with anthelmintic drugs or require surgical or endoscopic extraction of adult worms.
What are the preventive measures for ascariasis?
The best way to prevent ascariasis from humans or pigs is adequate sanitation.
Other preventive strategies include:
- Wash hands thoroughly with soap and water before handling food
- Wash, peel, and/or cook all raw vegetables and fruits before eating
- Avoid consuming uncooked or unwashed vegetables in areas where human or pig feces is used as fertilizer
- Do not defecate outdoors except in a toilet with proper sewage disposal
- Wash hands with soap and water after touching or handling pigs, cleaning pig pens, or handling pig manure
Parasites- Ascariasis. https://www.cdc.gov/parasites/ascariasis/
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