Ascaris worms live in the human small intestines for 10-24 months. Adult worms are occassionaly passed in the stool and may cause obstruction of the intestines or bile ducts.
Female worms produce large numbers of eggs that are passed in the stools (an estimated 200,000 eggs per day!). If these eggs are deposited in soil, they may become infective in 5 to 10 days if conditions are favorable.
What causes ascariasis?
Infection is caused by exposure to Ascaris eggs found in soil contaminated by human stool. Infection occurs when dirt or dirt-covered food items (i.e., farmed vegetables) are eaten. Children with dirty hands may consume the infective eggs by hand-to-mouth contact. Ascariasis is more common in non-industrialized nations and where hygiene and food-processing is poor.
Once in the small intestine, the ascaris eggs hatch to form larvae. The larvae invade the intestinal wall and enter the bloodstream, where they travel to the lungs. The larvae migrate out of the lungs into the back of the throat, where they are swallowed. The larvae then mature into adult worms in the small intestine and the process can be repeated.
What are the symptoms of ascariasis?
Despite the amazing life cycle of Ascaris in human infection (read above), most infections do not cause symptoms.
Severe infection (when a lot of worms are present in the intestines) may lead to...
- Poor weight gain and growth
- Intestinal blockage (vomiting and abdominal pain)
- Blockage of the bile ducts (jaundice, liver damage)
- Blockage of the pancreatic duct (pancreatitis, abdominal pain, vomiting)
When the larvae enter the lungs...
- Lung inflammation (cough, fever)
How is ascariasis diagnosed?
Ascaris eggs can be identified in stool samples viewed under a microscope. Adult worms are sometimes passed in the stool, and can be identified in a laboratory.
How is ascariasis treated?
An anti-helminthic drug (i.e., pyrantel pamoate, albendazole, piperazine, or mebendazole) can be given. Most of these medications paralyze the worms, which are then passed in the stools.
Surgery is rarely needed to help with removal of the worms.
How is ascariasis prevented?
- Proper disposal of human waste
- Proper washing of raw fruit and vegetables before eating
- Avoidance of areas with poor sanitation
- Proper washing of hands
Photo - An adult Ascaris worm. Diagnostic characteristics: tapered ends; length 15 to 35 cm (the females tend to be the larger ones). This worm is a female, as evidenced by the size and genital girdle (the dark circular groove at bottom area of image). CDC. Used with permission.
Last Updated (Monday, 22 June 2009 18:54)