What Are Intestinal Worms (Helminths)?

Human intestinal worms are parasites that live in the human intestine, eat bowel content or suck blood from the intestinal wall.

Intestinal worms may cause severe, life threatening infection, predominantly in children in tropical and subtropical areas where people often defecate on the ground: in rural parts of Africa, Middle East, South Asia, Indonesia and Central and South America. In people from Mediterranean parts of Europe or south parts of North America, they usually cause a relatively mild disease.

Presence of parasites of any kind (including intestinal worms) in or on the body is called infestation.

Helminth is a medical term for intestinal worm.

Symptoms of Infestation With Intestinal Worms

Intestinal worms may live in someone’s intestine for years without causing any symptoms. General symptoms may appear few weeks or several months after infestation and include paleness, weakness, tiredness (from anemia due to lost blood sucked by worms), restlessness, disturbed sleep and weight loss (due to loss of nutrients used by worms). Abdominal symptoms can last from weeks to months and include:

Sources of Worm Infection

Worm eggs, shed in the stool of humans or animals infected with adult worms, can contaminate soil or water. Once outside the body, eggs need several days or weeks to develop into the infective stage (cysts) or immature worms (larvae) that may be ingested when you eat with soil-contaminated hands or when you eat raw unwashed vegetables. Another source of intestinal worms is undercooked infected meat of domestic pig, freshwater fish or wild animals (bear, walrus, etc.). One can also be infected by ingesting dog’s fleas that have ingested parasitic eggs. Children may contract infection from sandboxes contaminated with pets’ stool. Certain types of immature worms may penetrate through your skin during swimming or walking barefoot; when they reach the small or large intestine they grow into adult worms.

Common garden worms usually do not cause illness in human. 

How Intestinal Worms Cause Disease?

Adult worms, which may be from 1 millimeter to several meters long, invade the bowel wall and suck the blood from it, or live freely in the intestine and utilize nutrients from the bowel content. The result are small intestinal or colonic inflammation and ulcers, anemia, and protein, iron and vitamin (mainly A, C, B12) deficiency. Intestinal obstruction may occur in severe cases. Larvae may migrate to other organs (liver, spleen, bladder, muscles, lungs, brain), where they form cysts and trigger allergic inflammation.

Common Human Intestinal Worms

A. Roundworms (Nematode) (1)

  • The large roundworms (Ascaris lumbricoides) are found worldwide. They are several inches long and thick as a pencil (Picture 1).
  • Hookworms (Necator americanus, Ancylostoma duodenale) are mostly found in tropical areas; they are about a half of inch long; they may be contracted by walking barefoot – they penetrate through the skin. Once in the intestine, they suck blood from the intestinal wall.
  • Whipworm (Trichuris trichiura), causing trichuriasis
  • Threadworms
    • Strongyloides stercoralis
    • Pinworm or seatworm (Enterobius vermicularis) is half an inch long, white  worm; its egs cause anal itch.
  • Trichinella spiralis, causing trichinosis, may be acquired by eating undercooked contaminated pork meet. Parasites move from the intestine into muscles and other organs where they form cysts – encapsulated forms, which are hard to eradicate. Main symptoms are abdominal pain, muscular and joint pain, swelling of the eyes and skin rash.

Roundworm - Ascaris lumbricoides

Picture 1. Roundworm -Ascaris lumbricoides (several inches long)
(source: phil.cdc.gov)

B. Flukes (Trematoda)

  • Schistosoma mansoni causes intestinal schistosomiasis (bilharziasis), mainly in Africa, Middle East, Caribbean and South America. It is about half an inch long and 1 millimeter thick. Adult parasites live in intestinal veins and release eggs into the intestinal hollow. Diagnosis is by finding eggs in the stool and urine.

Swimmer's itch - schistosome dermatitis, caused by flukes

Picture 2. Schistosome dermatitis (swimmer’s itch) -
- a rash on the lower arm on the sites of parasite entry
(source: phil.cdc.gov) 

C. Tapeworms (Cestoda)

  • Fish (broad) tapeworm (Diphyllobothrium latum) is contracted by infected freshwater fish; it may exceed 10 m; it appears in Europe, Russia and US.
  • Beef tapeworm (Taenia saginata) (Picture 3) and pork tapeworm (Taenia solium) may be contracted by undercooked beef or pork – mainly in rural areas, worldwide. Adult worms may be over 20 m long.
  • Dog tapeworm (Dipyllidium canium) is common in dogs and cats. Humans are (rarely) infected by ingesting dog fleas, infected with tapeworm larvae. Rice sized particles can be found in the stool.

Dog tapeworm - Taenia saginata

Picture 3. Beef tapeworm – Taenia saginata (several meters long)
(source: Wikimedia)

Trichicara cati or Trichicara canis can be attracted by ingesting eggs in cat’s or dog’s stool. After ingesting they develop into larvae that migrate through the body organs, like lungs. Common symptoms are fever and cough.

How Are Intestinal Worms Diagnosed?

If you suffer from unexplained abdominal bloating, diarrhea, weakness or weight loss, your doctor should suspect intestinal worms (or other intestinal parasites) as a possible cause. Diagnosis is confirmed by stool test for ova and parasites (O&P test). Hemoccult can reveal blood in the stool. Blood tests can reveal anemia (low ferritinand low red cells), low levels of vitamins A, C or B12, antobodies against certain worms, or elevated levels of eosinophils and IgEantibodies. Pinworm eggs from anal region can be collected by adhesive tape test.

Treatment of Intestinal Worms

A single dose of anti-worm drug, like mebendazole (safe for pregnant women), albendazole, diethylcarbamazine, ivermectin or praziquantel kills parasites in most cases. For some days after the healing, a stool-to-mouth auto-infection with eggs is still possible. Untreated infestations may last for years.

Prevention of Intestinal Worms

The following should prevent you from attracting intestinal parasites:

  • Wash the hands after visiting toilet, touching soil or pets, and before meal
  • Tell kids to avoid touching mouth and nose with their hands
  • Do not walk barefoot and swim in lakes in tropical areas
  • Avoid suspicious restaurants with poor hygiene
  • Cook meat and fish well

References:

  1. Parasitic roundworms  (niaid.nih.gov)
  2. Bilharziasis  (emedicine.medscape.com)

Article reviewed by Dr. Greg. Last updated on April 23, 2011