ball01e.gif Introduction

  Most of nematodes in the human intestine are maintained of their life cycle by soil. The soil is indispensible for incubation and transmission of eggs or larvae of the nematodes. These are Ascaris, Trichuris, Strongyloides, and hookworm. They are highly prevalent in developing countries at temperate zone as well as tropical zone, and thus shoule be a major target in public health.

ball01e.gif Types of Soil-Transmitted Helminths

Ascaris (Round-worm)

    ball03f.gif Distribution.
    Spread widely in the world
    ball03f.gif Life cycle.
    Parasitic region is small intestine.
      Eggs in soil with right conditions, such as temperature, and humidity, develop into the infective larvae - Enter the body taken into the mouth - Eggs are exuvially hatched out - The hatched larvae actively migrated into the intestinal wall, then into the portal circulation to liver, the right heart, and on into the pulmonary vessels to the interalveolar tissues of the lungs - After growth and essential develop in the lung, the larvae migrated or carried in the mucus flow through the respiratory passage to the throat and are swallowed.
    ball03f.gif Pathology and Symptoms.
    1. Due to Larva migrans
      While Ascaris migrate into the intestinal wall or lung, they cause bleeding by destroying capillary or
    cause ascariasis pneumonia by secondary infection.  
    Larva may migrate into brain, spine, or kidney
    through circuratory.
    2. Due to the
    Larva take the nutrition from the small intestine, and enzyme from the Larva inhibits digestion of the host and causes symptoms such as indigestion, over- or in-appetence, diarrhea, aneilema, cephalalgia, nausea, allergic symptoms such as hives, cough, status asthmaticus, oliguria, and geophagia.

Enterobius vermicularis (Pinworm)

    ball03f.gif Distribution.
    Spread widely in the world.
    ball03f.gif Life cycle.
      Parasitic region is cecum, appendix vermiformis, colon, etc.
      Eggs excreted to outside are infective since they already include larvae.  Eggs are taken into mouth and hatched in small intestine and parasitize in cecum, colon, etc.
    ball03f.gif Pathology and symptoms.
      When a female oviposits eggs near anus, or perineum, host feels serious itch.  This itch causes rubber and swelling near anus, and eventually the secondary infection.
      Somnipathy, anepithymia, disethesia, hypernoia, and even paroxysm maybe observed in kids.  This
    parasite also cause gastrointestinal disturbance, such as aneilema, nausea, vomiting, diarrhea, and ulcer in rectum.

Trichuris (Whipworm)

    ball03f.gif Distribution.
    Spread widely in the world.  Usually detected with Ascaris.
    ball03f.gif Life cycle.
      Parasitic region is lower large intestine, cecum, appendix vermiformis, colon, rectum, etc.
      The eggs are discharged and passed in the feces in the unsegmented stage and require at least 10 to 14 days for embryonation in the soil.  People become infected on swallowing the fully embryonated eggs.  The larva hatches in the small intestine and enters the crypts of the lower cecum and colen, eventually entering the eputhelium of the other parts of the large intestine.
    ball03f.gif Pathology and symptoms.
      Normally, people are infected with less than 10 trichuris and no major symptom may be observed.  Long and thin front part of the parasite may cause retraction and bleeding of intestine mucosa.
      If the count of parasite is more than 200, bleeding and infection near large intestine mucosa,
    hematochezia, dysentery, maldigestion, aneilema, appendicitis, in-appetence, loss of weight, aglobulia, and evenproctoptosis may be observed.  Eosonophilia, allergic symptoms such as hive also related with the number of parasite.

American hookworm, and hookworm

    ball03f.gif Distribution.
      American hookworm: South of United States of America, Central and South America, Africa, Southeast Asia, and Australia.
    Hookworm: Tropical and subtropical regions.
    ball03f.gif Life cycle.
      Parasitic region is upper small intestine, especially upper jejunum. Eggs excreted to the outside with
    feces - Under the right temperature (about 30”ĘC) and circumstances, hatch for 24~48hours - Exuviate after about 7days - filamentous larvae, which are very infectious to human being, can survive more  than 2 weeks and infectious on the skin contact - Arrive in lungs after passing heart and pulmonary artery through venula and lymphatic vessel - When migrated into the small intestine through respiratory tract, pharynx, esophagus and gaster, larvae grow into the adults.
    ball03f.gif Pathology and symptoms.
      Pneumonia symptoms may observed due to the infection caused by the destruction of alveoli pulmonis during the migration of larvae While adults, which parasitize in the small intestine, suck blood, they also release anticoagulant.   American hookworm: Usually infection occurs on the skin contacts.  While the hookworm penetrates skin, dermatitis, itch, erythema, comedo, and blister may be observed.
    Hookworm: Usually infection occurs while the larvae was orally taken.

Strongyloides (Threadworm)

    ball03f.gif Distribution.
    Spread widely in the world.
    ball03f.gif Life cycle.
      Parasitic region is upper small intestine.  
      Only female is found in parasitic generation, and the size is 2.2mm-30~76mm.  On contact with the skin of human beings, the filariform larvae penetrate to the small cutaneous blood vessels and are carried to the lungs.
    ball03f.gif Pathology and symptoms.
      Aneilema, diarrhea, vomiting, and eosinophilia may be observed.  In case of immunosuppression, larva migrated into the prerenal viscus and cause severe pneumonia, infection in enteron, chronic diarrhea with mucous and bloody stool, and even death.

  1”­8. Egg of Ascaris lumbricoides : 1”­2. Fertilized egg ; 3. Unfertilized egg ; 6.   Decorticated egg of its outer albumin coat ; 7”­8. Embryonated egg, including a   larva in the egg shell ; 9”­10. Adult female worms ; 11. Three lips at the mouth   end, SEM view.


      1”­3. Egg of Trichuris trichiura ; 4. One pair of T. trichiura ; 5. Adult female ; 6. Adult male.
                                           (a, male ; b, female ; c, stichosome in the anterior slender part)

1”­2. Egg of hookworm ; 3. SEM view of Ancylostoma duodenale buccal cavity showing two pairs of teeth ; 4. Anterior end of a female Necator americanus ; 5. Posterior end of a female N. americanus ; 6. Buccal canity of N. americanus showing one pair of cutting plate


1. Egg of Enterobius vermicularis ; 2. SEM view of an egg ; 3. Adult female E. vermicularis