Ascariasis

Ascariasis lumbricoides nematode worms (male on left, female on right); females can reach lengths of over 12 inches (26.4 cm); SOURCE: CDC

Ascariasis is one of the tropical diseases caused by the parasite Ascaris lumbricoides, a large nematode (roundworm) that infects humans in the gastrointestinal tract and requires human infection to complete its complex life cycle. Another species, Ascaris suum, which infects pigs may occasionally infect humans.

Life cycle of Ascaris lumbricoides; SOURCE: CDC

Ascaris lumbricoides, also known as roundworm, Ascaris worms, or giant roundworm, is a nematode parasite that can infect humans by residing in the gastrointestinal tract or in other areas of the body such as the lungs. The worms have a worldwide distribution but are most common in tropical and subtropical areas where humans have poor sanitation and where human feces are used as soil fertilizer. Many individuals infected show no symptoms, but abdominal discomfort and/or cough are two major symptoms of infection.

The roundworms are the largest nematode parasites that live in the human intestine. Figures 1 and 2 show how large and how numerous these intestinal parasites can be. Figure 3 shows the life cycle of the worms in the human—from ingestion to penetration of the intestinal lining to migration and maturation in the lungs, migration to the throat, and then to the small intestine where they mature and produce eggs that are passed with stool, where they await ingestion by other humans.

Worm infections (helminthic or helminth infections) are a group of diseases caused by parasites transmitted through contaminated soil. These parasites include whipworms, hookworms, and roundworms (Ascaris and Strongyloides that cause strongyloidiasis). The diseases they cause are termed helminthiasis. This article is limited to Ascaris lumbricoides infections.

Mass of Ascariasis lumbricoides worms passed rectally by a child in Africa; SOURCE: James Gathany/CDC

The cause of ascariasis is the invasion, spread, and eventual maturation of Ascaris lumbricoides in the human host.

The symptoms described below are due to the parasite's ability to penetrate the intestinal tract and proceed from there to the lungs where they eventually mature further and penetrate the air sacs of the lungs, migrate to the throat, and are subsequently swallowed to allow maturation in the intestinal tract.

Although the nematodes exist worldwide, the most common areas they inhabit are areas where the climate is warm and moist such as tropical and subtropical regions of the world. The highest risk factors for contracting this infection are poor sanitation and poor hygiene.

Ascariasis is transmitted indirectly in most cases by an uninfected individual ingesting contaminated food or water that contains the Ascaris eggs deposited by infected humans in their feces into the environment. Children are commonly infected in these areas; school-age children are more frequently infected than adults are.

Microscopic appearance of a fertilized egg from Ascaris lumbricoides; SOURCE: CDC

The incubation period is variable because the parasite's life cycle may take four to eight weeks to be completed. The signs and symptoms of the nematode infection by Ascaris lumbricoides may include the following:

• Abdominal discomfort
• Abdominal cramping
• Abdominal swelling (especially in children)
• Fever
• Coughing and/or wheezing
• Nausea
• Vomiting
• Passing roundworms and their eggs in the stool

Health care providers easily diagnose infection by examining the stool sample from the patient using a microscope to identify Ascaris lumbricoides eggs. In some instances, stool particles are concentrated to increase the likelihood of finding the nematode eggs.

Other tests that suggest infection include blood tests that show eosinophilia (the increased presence of a certain type of white blood cell); abdominal X-rays and/or ultrasound studies may detect a large mass of worms in the intestines.

Once diagnosed, primary care physicians can treat most patients for ascariasis.

However, if complications like bowel blockage or intestinal perforation occur, other doctors such as a surgeon and/or infectious disease specialist may need to be consulted. Other severe complications can involve the lungs and may require a lung specialist (pulmonologist) to be consulted.

Fortunately, there are effective anthelmintic treatments available for ascariasis. Medications such as

• Dingle-dose albendazole (Albenza) or mebendazole (Vermox) are drugs of choice for ascariasis.
• Health care providers administer drugs for only about one to three days.
• Other drugs such as ivermectin (Stromectol), levamisole (Ergamisol), pyrantel pamoate (Pin Rid, Pin X), nitazoxanide, and piperazine citrate have also been used effectively.
• Pyrantel pamoate treats pregnant women; other drugs like mebendazole and albendazole may cause teratogenic effects in the fetus.

There are a number of home remedies for ascariasis, including:

• Garlic
• Wormwood,
• Pumpkin seeds
• Many other herbs

However, infected individuals should check with their doctor before utilizing any of these home remedies as their effectiveness might not be as good or as fast as the prescription medications described in the treatment section.

There are a number of complications that may occur with untreated ascariasis. Following is a list of these complications:

• Bowel obstruction (intestinal blockage)
• Pancreatitis (inflammation of the pancreas)
• Cholecystitis (inflammation of the gallbladder)
• Peritonitis (inflammation of the abdominal cavity lining)
• Intussusception (an intestinal condition in which part of the intestine is pulled into itself, creating an obstruction)
• Volvulus (abnormal twisting of the intestine)
• Peritoneal granulomas (scar tissue lining the abdomen)
• Hepatic (liver) abscesses
• Pneumonitis (inflammation of the lungs)
• Death

Organs other than the intestinal tract and lungs may be occasionally involved; some patients may have allergic reactions that may become severe. About 11,000 deaths occur each year worldwide due to intestinal obstructions caused by ascariasis, with the majority of patients being children.

The prognosis of ascariasis for appropriately diagnosed and treated ascariasis is very good. However, the prognosis begins to decline if the patient develops a high number of worms in the body (worm burden). This worm burden can lead to more serious complications such as intestinal obstruction and worsens the prognosis of this disease. A female worm may reach a length of 14 inches (35cm).

An interesting additional effect of ascariasis may be increased fertility in women who have the infection. Researchers in Bolivia suggest that the worm alters the immune system for its own protection that results also in allowing females to become pregnant easier. The mechanism of this enhanced fertility is unknown, but researchers suggest it could lead to development of fertility-enhancing drugs.

Yes, it is possible to prevent ascariasis; before handling or eating any food, wash hands with soap and water, and avoid drinking any local water sources when traveling. Use only boiled water or bottled water and avoid raw vegetables and fruits unless you can clean them yourself.

While traveling, eat only foods that are cooked well and served hot. In addition, reinfection is possible for people who live in areas where ascariasis infections are common. Consequently, health care providers give some individuals, especially children, prophylactic doses of medication (such as ivermectin) every two or three years in some countries. The World Health Organization (WHO) estimates that up to 10% of the developing world's population has intestinal worm infections, with total worldwide deaths due to Ascaris infections at 60,000 per year, mainly occurring in children.