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.
Types of Soil-Transmitted
Spread widely in the world
Parasitic region is small intestine.
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.
Due to Larva migrans
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
2. Due to the Larva
take the nutrition from the small intestine, and enzyme from
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)
Spread widely in the world.
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.
When a female oviposits eggs
near anus, or perineum, host feels serious itch. This
itch causes rubber and swelling near anus, and eventually the
disethesia, hypernoia, and even paroxysm maybe observed in kids.
parasite also cause gastrointestinal disturbance,
such as aneilema, nausea, vomiting, diarrhea, and ulcer in rectum.
Spread widely in the world. Usually detected with Ascaris.
Parasitic region is lower large intestine,
cecum, appendix vermiformis, colon, rectum, etc.
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.
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
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
American hookworm: South of United States of America,
Central and South America, Africa, Southeast Asia, and Australia.
Hookworm: Tropical and subtropical regions.
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.
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.
Usually infection occurs while the larvae was orally taken.
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.
male ; b, female ; c, stichosome in the anterior
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
Egg of Enterobius vermicularis ; 2. SEM
view of an egg ; 3. Adult female E. vermicularis