Hookworms
The hookworms live in the upper part of small intestine. They feed on
the blood and cause hookworm disease, which is one of the five major
parasitic diseases in China. Two species, Ancylostoma duodenale（十二指肠
钩口线虫）and Necator americanus（美洲板口线虫）, are prevalent in our
country.
I. Morphology
1. Adults: They look like an odd piece of thread and average about 1cm.
They are white or light pinkish when living. Their strong mouth cavities are
armed with teeth or cutting plates. The female is slightly larger than the male.
The male’s posterior end is expanded to form a copulatory bursa.
Morphological Differences between Two Species of Hookworms
—————————————————――——————————
A. duodenale
N. americanus
———————————————————――—————————
Size
about 1 cm, larger
smaller
————————————————————――————————
Shape single curve, looks like“C” double curves, looks like“S”
—————————————————————――———————
Mouth 2 pairs of ventral teeth
1 pair of ventral cutting plates
——————————————————————――——————
♂Copulatory 1 pair with separate
1 pair which unite to form
Spicule
endings
a terminal hooklet
———————————————————————――—————
♀caudal spine
present
no
————————————————————————――————
♀vulva position post-equatorial
pre-equatorial
—————————————————————————――———
2. Egg: 60×40μm, oval, shell is thin and colorless, content is 2-8 cells.
Differences between Decorticated Ascaris and Hookworm eggs
－————————————————————————————
Decorticated ascaris egg
hookworm egg
—－———————————————————————————
Shell
thick
thin
——－——————————————————————————
Egg cell
unsegmented
4-8cells
———――————————————————————————
Space between
shell and cell
new-moon shaped space
between cell and ends of shell
empty space surrounding
the segmented cells
———――————————————————————————
II. Life Cycle
1.Geohelminth, 2.Final host: man, 3.Inf. Stage: Larva 3 or filariform
larva, 4.Inf. Route: by skin, 5. Feeding habits: blood, 6. Blood loss:
0.02~0.1ml/Na/day；(0.02~0.1) × 7 ml/Ad/day, 7. Site of inhabitation: upper
part of small intestine, 8. Life span: average 3 years, Ad 7 years, Na 15 years,
9. Egg output: 10,000~30,000/Ad/day；5000~10,000/Na/day, 10. Blood-lung
migration: skin—venacava—right heart—lungs
**Question: How many differences are there between the life cycles of
Ascaris and Hookworm?
Filariform
heart-------
penetrate skin
larvae-------------------------------Venacava--------via
vessels
or
Right
lymphatics
expectoration---death
Lungs
(alveolus,
bronchiole,
bronchus)-----Trachea-----Pharynx---------------molt 3,4
Passed in feces
swallowed
Duodenum----------- ♀ ♂ Adults-------Eggs ------------------ Outer
environment
20-30℃, humidity 80%
-----------------------------out---------------24hrs
Rhabditiform
molt2
Rhabditiform
larvae
molt 1, 48hrs
1(L1)
hatching
survive 15wks in moist soil
larvae2(L2)---------Filariaeform
larvae
(L3)------------------------Waiting for the host in soil or on grass or crop
whole process 5-7weeks
III. Pathogenesis and Clinical Manifestations
1. Larval migration phase
(1) Dermatitis is also known as "ground itch" or "stool poison". The
larval penetration of skin causes a locally allergic reaction, the petechiae（瘀
点）with an itching and burning sensation. Scratching leads to secondary
infection. The skin lesions heal within 2 weeks.
(2) Pneumonitis (allergic reaction; Loeffler's syndrome): The migrating
larvae damage the alveolar capillaries and patients manifest cough, asthma,
low fever, blood-tinged sputum or hemoptysis （ 咯 血 ） , chest-pain,
inflammation shadows in lungs under X-ray and eosinophilia（嗜酸性粒细
胞增多）. These manifestations go on about 2 weeks.
2. Adults in small intestine
(1) A large worm burden results in microcytic hypochromatic anemia
(*characteristic manifestation). The symptoms are lassitude, edema,
palpitation of the heart. In severe case, death may result from cardiac failure
or physical exhaustion.
**The anemia results from hookworms sucking blood and excessive
blood loss. The excessive blood loss is due to the large worm burden; worms
secreting several antiagglutinating materials (antiagglutinin 抗凝素, and
etc.), often changing the place to suck blood and discharging undigested
blood; the old injured sites of the intestinal wall continuing to bleed. The
other reason for the anemia is that the patient can not get enough noutrition.
(2) Allotriophagy ( allotriophagia, geophagia or pica 异嗜症) is due to
the lack of trace element iron (ferrum)
(3) Epigastric pain as that of a duodenal ulcer; dearrhea.
(4) Amenorrhea, sterility, abortion may occur in the women.
(5) Gastrointestinal bleeding
(6) Infantile hookworm disease
IV. Diagnosis
Diagnostic criterion: 1. hemoglobin is lower than 12g/dl in man, 11g/dl in
woman. 2. find hookworm eggs.
Method: 1. saturated brine flotation technique is first choice.
2. direct fecal smear
3. larval culture
V. Treatment & Prevention
1. Albendazole or Mebendazole; 2. Avoid the skin contacting with the
infective larvae in soil or on plants.
VI. Epidemiology
Both species of hookworm are prevalent in the tropics and subtropics.
The optimal temperature for Ancylostoma duodenale is 22-26 ℃ , so
Ancylostoma duodenale is mainly prevalent in the north of China. Necator
americanus is mainly distributed in the south of China due to it prefer the
temperature of 31-35℃.
*Factors favoring the hookworms spread:
1. Simple life cycle (geohelminth).
2. Pollution of the soil by human feces containing enormous hookworm
eggs.
3. Warm and moisture climate is favorable for the development of
hookworm eggs and larvae.
4. Human gets infection by the skin contacting with the infective larvae in
fertilized soil or on plants. The hookworm incidence of barefoot farmers
is the highest.
VII. Prevention
Unified measures: 1. Sanitary disposal of night soil, 2. Individual
protection, 3. Health education, 4. Cultivating hygienic habits, 5.
Treatment of the patients and carriers.
Enterobius vermicularis (pinworm)
It is commonly found infecting humans, especially in children. The
adult worms inhabit the cecum and adjacent intestinal lumen. Right after
mating, the male dies. Therefore, the male worms are rarely seen. The
female worms migrate down the intestinal tract. At midnight, when the anal
sphincter is relaxed, the worms migrate out the anus depositing eggs on the
perianal skin and causing perianal itch. Humans get the infection by mouth
or retro-infection, and by the mode of auto-infection or foreign infection. It
is commonly found in kindergarten and primary school students.
I. Morphology
The female adult looks like a pin, measures about 1 cm and is white in
color. The fusiform body terminates in a long, thin, tapering tail. The
anterior end tapers and is flanked on each side by cuticular extensions called
“alae”（颈翼）. The esophagus terminates in a prominent muscular bulb
（esophagus bulb 食道球）. The male adult is only about one-third to
one-half the size of a female and has a curled tail.
The eggs are persimmon seed-like, about 55×25  m. it is clear,
colorless and contains a larva.
II. Life cycle
1. Site of inhabitation: ileocecum; 2. Infective stage: embryonated eggs;
3. Source of infection: auto-infection and foreign infection; 5.Inf. route: by
mouth or by retro-infection; 5. No intermediate and reservoir hosts; 6. Egg
output: 5,000-15,000/♀/a life; 7. Life span: ♀1 month; 8. Feeding habits:
blood, tissue fluid and intestinal contents; 9. Site of oviposition: perianal
skin.
Migrates out anus
35℃, humidity 95%, 6hrs
Pregnant♀----------------------eggs ---------------------------Embryonate eggs
At mid night, deposits
perianal skin
swallowed by man
-----------------------Larvae
intestine-----------------cecum-----or retro-infection
♀♂adults mate
migrate down
hatching
out
in
(2-6 wks)
III. Symptomatology
About one-third of pinworm-infected persons are asymptomatic. The
major symptom, anal itch, is associated with the nocturnal migration of the
gravid females from the anus and deposition of eggs in the perianal folds of
the skin.
(1) In children: Anal pruritus (anal itch) results in scratching anus,
restlessness, grinding their teeth in sleep, nervousness, irritability, divided
attention and poor school record.
(2) Ectopic injure: In young girls, migration of the worms may produce
vaginitis, urethritis, and rarely peritonitis, egg granuloma of abdominal
cavity, salpingitis giving rise to sterility.
IV. Diagnosis
*Cellophane tape technique is first choice. *The examination should be
made in the morning, before the patient has not washed the anus or
defecated.
V. Treatment and Prevention
1. Albendazole or Mebendazole is very effective. Since the life span of
the pinworm is about one month, the major problem is re-infection.
Repeated treatment may be necessary for a radical cure.
2. Carry out the general survey and treatment.
3. Carry out the health education and cultivate hygienic habits
VI. Epidemiology
Enterobiasis is widely prevalent all over the world even in cold or
developed countries. Its epidemiological characteristics include that the
incidence is higher in children than adults; it is most common where people
live under crowded conditions such as orphanages, kindergartens, refugee
camps and large families; the infection and re-infection are very easy due to
the simple life cycle and the infective route of anus-fingers-mouth..
Question:
What
are
enterobiasis?
the
epidemiological
characteristics
of