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Ascariasis is a type of roundworm infection. Roundworms are parasites that use your body as a host to stay alive and reproduce, maturing from eggs to adult worms inside your body. Ascaris eggs are microscopic, but the adult worms are the largest of the intestinal roundworms, reaching lengths up to 40 centimeters, or about 15 inches.

Ascariasis is the most common type of roundworm infection in humans, infecting approximately 25 percent of the world's population. The highest rates of infection occur in developing countries. In the United States, ascariasis is more common in rural areas with warm climates, with a higher infection rate in the South.

Most of the time, ascariasis causes no symptoms, or only mild stomach or digestive problems. But when your body is infested with hundreds of worms, more serious symptoms and complications can occur. The good news is that ascariasis can be treated effectively with medication. There also are simple steps you can take to prevent ascariasis, mostly involving good hygiene and proper sanitation.

Mild ascariasis — with only a few parasites in your body — may cause no symptoms. Symptoms occur with moderate or heavy infestations, sometimes progressing as the parasite migrates through your body. After you ingest ascaris eggs, they hatch in your intestine and the larvae migrate into your lungs. At this stage, you may experience symptoms similar to pneumonia, including:

• Persistent cough
• Shortness of breath
• Wheezing

The ascaris larvae eventually reach your throat, where they are coughed up and then swallowed. They then enter the intestine, where they mature and mate. In mild or moderate ascariasis, the intestinal infestation can cause:

• Vague abdominal pain
• Nausea and vomiting
• Diarrhea or bloody stools

If you have a heavy intestinal infestation — a large number of worms — you may experience:

• Severe abdominal pain
• Fatigue
• Vomiting
• Weight loss
• A worm in vomit or stool
• A worm emerging from nose or mouth

About two months after you first get ascariasis, the mature worms begin laying eggs in your intestine. These microscopic eggs travel through your digestive system and eventually can be found in your feces. Eggs require 10 to 14 days in soil at warm temperatures to become capable of infecting a new host, and can remain viable in the soil for up to six years. When the eggs are ingested, the life cycle begins again. Adult worms can live up to two years, and female worms can produce more than 200,000 eggs daily.

The parasite can be transmitted when infected human feces are mixed with soil. In many developing countries human feces are used for fertilizer, or poor sanitary facilities allow human waste to mix with local soil in yards, ditches and fields. The eggs can survive in soil for years to reinfect members of the community. The eggs infect their hosts when humans eat the contaminated vegetables and fruit grown in that soil.

Risk factors for ascariasis include:

• Poor sanitation and the use of human feces as fertilizer. Ascariasis is more widespread in developing countries where human feces are allowed to mix with local soil. There, the eggs become infective and are capable of infecting people who eat produce grown in it or otherwise ingest the eggs.
• Warm climate. Ascaris worms thrive in milder climates. In the United States, ascariasis is more common in the South. But it's more prevalent in developing countries with warm temperatures year-round.
• Heredity. Some studies have suggested that heredity may play an important part in susceptibility to ascariasis.

If you have gastrointestinal problems that won't go away, such as abdominal pain, diarrhea or nausea, consult your doctor.

However, if you have only mild ascariasis, you may never need medical attention. While symptomatic infections usually warrant treatment, infections with no symptoms typically don't need to be treated. In some cases, ascariasis will resolve on its own. This occurs when there are no male worms to mate with females and the females eventually die.

About two months after you ingest ascaris eggs, the ascaris worms mature and begin laying thousands of eggs a day. These eggs travel through your digestive system and eventually can be found in your stool. To diagnose ascariasis, your doctor will examine your stool for the microscopic ascaris eggs and larvae. In heavy infestations, it's possible to find worms after you cough or vomit, and the worms can come out of other body openings, such as your mouth or nostrils. If you notice anything resembling a worm when you cough or vomit, or if one emerges from your nose or mouth, keep it to let your doctor examine it.

Complications related to typical ascariasis are rare. However, potentially dangerous complications can develop if you have a heavy infestation.

• Nutritional deficiencies. Children with ascariasis are especially at risk of nutritional deficiencies. Loss of appetite and insufficient absorption of digested foods can occur as a large number of parasites take nourishment from the host's body.
• Intestinal blockage and perforation. In heavy ascariasis infestation, a mass of worms can block a portion of the intestine, causing severe abdominal cramping and vomiting. The blockage can even perforate the intestinal wall or appendix, causing hemorrhage or appendicitis.
• Allergic reactions. Some people develop allergic reactions to the ascaris worm's metabolic excretions and secretions, or to dead and dying worms. These reactions can cause signs and symptoms such as asthma, insomnia, eye pain and rashes.

Anti-parasite (antihelminthic) medications are the first line of treatment against ascariasis. The most common are mebendazole (Vermox), albendazole (Albenza) and pyrantel (Antiminth, Pin-Rid). These medications work by killing the adult worms as well as the larvae and eggs to prevent reinfection. You may have mild gastrointestinal side effects during the course of treatment, and you may need to take multiple doses to get rid of the infestation completely.

Surgery
In cases of heavy infestation, surgery may be necessary to repair damage the worms have caused and to remove worms. Intestinal obstruction or perforation, bile duct obstruction and appendicitis are complications that may require surgery.

The best defense against ascariasis is good hygiene and common sense. Follow these tips to avoid infection:

• Practice good hygiene. Ascariasis is spread by ingesting parasite eggs from contaminated soil. Before handling food, always wash your hands with soap and water, and wash fresh fruits and vegetables thoroughly.
• Use care when traveling. Ascariasis is the most common roundworm infection in the world, with higher infection rates in developing and warm-climate countries. When traveling, use only bottled water and avoid raw vegetables unless you can peel and wash them yourself. As a rule, eat only foods that are hot and cooked.