Threadworm infection (strongyloidosis)

Strongyloidosis (also called strongyloidiasis) is an intestinal worm infection. Intestinal worms are a type of parasite -- an organism that survives by feeding on other organisms or hosts. Parasites can inhabit the human body or live in soil, water, food or insects. Some parasites exist naturally in the human body, but are usually controlled by the immune system.


Causes/associated factors
Infection with the intestinal worm Strongyloides stercoralis causes strongyloidosis, which is sometimes called threadworm. (However, a pinworm infection may mistakenly be referred to as threadworm). The infection can be found worldwide, typically in tropical and subtropical regions and where people are exposed to overcrowded or unsanitary conditions. The infection is rare in the United States. When it does develop, it's found mostly in the southeastern states due to the favorable climate. The infection is most serious in people whose immune systems are not functioning normally (due to cancer, HIV infection or long-term treatment with steroid medication, for example).

Transmission
Strongyloides have a complicated life cycle. Infection occurs after infective strongyloides larvae (immature worms) that live in the soil penetrate the skin and travel through the bloodstream to the lungs. From there, they move up the bronchial passages in the lungs and are eventually swallowed. When the larvae reach the small intestine, they mature and begin producing eggs. These eggs develop into noninfective larvae in the intestine. Some larvae pass out of the body in the feces and develop into infective larvae in the soil, capable of repeating the cycle in another host. Some noninfective larvae become infective while still in the small intestine. They can penetrate the intestinal wall or skin around the rectum, travel through the bloodstream to the lungs, and reinfect the host. Reinfection can lead to a persistent or severe infection, usually in people who have weak immune systems.
An infected person will begin passing larvae in his or her stool about two to four weeks after being infected. If left untreated, strongyloidosis may continue for up to 35 years. Larvae are produced during this time and the infected person remains contagious (capable of spreading the infection to others).


Signs/symptoms
For about 50 percent of otherwise healthy people, strongyloidosis has no symptoms. People whose immune systems are not functioning normally may have more frequent and severe symptoms. First, an itchy rash may develop at the point where the larvae entered your body. When they pass through your lungs, they may cause a cough with blood-tinged sputum or difficulty breathing. Intestinal symptoms may include abdominal pain, bloating, vomiting and diarrhea consisting of large stools containing mucus.

Diagnosis
Diagnosis is based on the presence of larvae in a stool sample. Several stool specimens may be needed. If repeated tests are negative, a sample of contents from the upper intestine may be examined. The sample may be taken through a tube that's passed from the nose into the stomach and upper intestine or by swallowing a specially designed string. If the parasite has invaded your lung tissue, the larvae may also be identified in your sputum. A blood test may detect an unusually high concentration of eosinophils (a type of white blood cell known to destroy parasitic organisms) in your blood.

Treatment
A strongyloide infection is usually treated with the medications ivermectin or thiabendazole. The doctor may recommend a repeat stool sample test later.

Complications
The larvae may migrate to many body organs, causing various symptoms that may result in serous tissue damage. In some cases, the infection is life-threatening. Complications are more likely in people who have weak immune systems.

Pregnancy-specific information
A variety of medications may be prescribed for various intestinal worm infections, but certain standard medications should not be taken if you're pregnant. Thoroughly discuss your health history with your doctor and review the risks and benefits of any treatment. If you don't have significant symptoms, your doctor may recommend postponing treatment until after delivery.
If you are or may be pregnant, you may want to avoid traveling to areas with poor sanitation, where you're more likely to develop parasitic infection(s). If you do travel to these areas, be sure to follow the preventive measures outlined below.


Senior-specific information
Growing older is not a risk factor for this condition.

Prevention
To prevent intestinal worms of any type, follow these general guidelines:
Practice sanitary hygiene habits, especially when disposing of human waste. Never wipe feces on the ground, and dispose of diapers properly.

Wear shoes in areas where the soil or sand may be contaminated with feces or parasites. Don't sit directly on the ground or handle the soil or sand with your bare hands.

Wash your hands thoroughly with soap and water or an antibacterial handwashing solution before handling food or water and after using the toilet or changing diapers.

Wash, peel or cook raw fruits and vegetables before eating.

Cook meat thoroughly, to at least 160°F. It should no longer be pink in the center. Measure the internal temperature to assure doneness. Keep in mind that curing, smoking, drying or microwaving meat may not kill all worms.

Slabs of pork less than 6 inches thick can be frozen at 5°F (-15°C) for 20 days to kill any worms. Freezing may not be effective for wild game.

If you're traveling abroad, it's wise to avoid uncooked fruits and vegetables, unless you've peeled them yourself; raw or undercooked meat, poultry, fish and eggs; foods prepared in advance that haven't been kept cold or very hot; and foods purchased from street vendors. If you have any doubts about a food's safety, follow this simple rule: Boil it, cook it, peel it or forget it.

If you're unsure of the safety of drinking water (such as in areas where the water isn't chlorinated or hygiene and sanitation are poor), ensure water safety by boiling your water vigorously for one minute, filtering it or treating it with iodine or chlorine. Drink only this water, beverages made from it, canned or bottled carbonated beverages (including water and soft drinks), beer or wine. Wash uncooked fruits or vegatables using treated or filtered water. Avoid using ice cubes and drinking from unclean glasses and wet or dirty cans or bottles. (It's best to drink straight from the can or bottle after wiping it clean and dry.) Don't brush your teeth in tap water, and avoid swallowing water while swimming or bathing.