Strongylid Nematodes Hookworms Chap. 25

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Strongylid Nematodes - Hookworms - Chap. 25

• Hookworm disease is one of the most important
  parasitic diseases of humans.
• Number of humans infected is estimated at 1.2
  billion with 50,000 to 60,000 deaths each year.
• Hookworms occur Wisconsin - 4.9 prevalence in
  1987 survey but are not endemic here
• cases in WI?
•  

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2 species of hookworms infect humans
1. Ancylostoma duodenale - Old World
Hookworm Distribution  
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2 species of hookworms infect humans
2. Necator americanus - New World
Hookworm Distribution Also occurs in Africa
and Asia - probably introduced into the U.S. with
the slave trade. Stereotyped rural southerner as
lazy, shiftless, and good-for-nothing (poor white
trash) is partly due to the high prevalence of
this parasite in southern U.S.  
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Hookworm Distribution
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Females 9-13 mm long with egg-filled uterus
Male hookworms 7-11 mm long Posterior end
forms a __________________
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Morphology of Ancylostoma duodenale
Buccal capsule contains 2 pairs of large ventral
(anterior) teeth Copulatory bursa
is at posterior end and contains 2 thin spicules
that separate distally.
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Morphology of Necator americanus
Buccal capsule contains a pair of ventral and
dorsal cutting plates. Copulatory
bursa contains spicules that are fused distally.
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Life Cycle of 2 Hookworms is similar
1. Adults occur in the human __________________
Male and female are commonly found in copula.
Both are well attached to the intestinal mucosa
with the buccal capsule. 2. Female releases eggs
which are passed in the feces. Both species
show high fecundity A. duodenale produces 25,000
to 30,000 eggs/day. N. americanus produces 9,000
eggs/day.
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Life Cycle of 2 Hookworms is similar
3. Eggs embryonate in warm, moist shady soil. 4.
In 1-2 days, the __________ (also called the
rhabditiform larva) hatches and feeds on bacteria
and debris in the feces soil. 5. L1 molts
twice to the ______ stage (called the filariform
larva) in a week.   6. L3 are infective and
migrate to the surface of the soil and upon
contact with human skin will______________________
Larvae typically penetrate skin of the feet
when one walks barefooted through warm soil.
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Life Cycle of 2 Hookworms is similar
7. After penetrating the skin, the L3 enter the
circulation, are carried to the heart, and follow
the pulmonary circulation to the
______________________ Here, they break out of
the lung capillaries, enter the alveoli, migrate
up the respiratory tree, and are swallowed.   8.
Arriving in the small intestine, the L3 molts
twice to the adult stage. It takes 5 weeks from
the time of skin penetration until the
adults are mature.
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Pathology

• Extent of pathology is associated with the
  numbers of adults
• Symptoms appear in infections of 100 or more
  worms.
• A heavy infection involves 500 or more worms.
• Symptoms are severe and the infection may be
  life-threatening.
• 1. _____________________________ - penetration of
  L3 into the skin, usually the feet itching and
  reddish rash occurs.
• 2. ______________________________-
  pneumonia-like symptoms occur as L3 break out of
  the capillaries and enter the alveoli
• (symptoms are not as severe as Ascaris migration)

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3 Phases of Pathology

• 3. __________________________ - adults attach to
  the mucosal wall and may penetrate into the
  submucosa where they voraciously suck blood - up
  to 200 ml of blood may be lost/day
•  A. duodenale takes 0.26 ml/day N. americanus
  0.03 ml/day
•  Hookworms are very wasteful, as most of the
  blood taken simply passes through its intestine
  but is lost to the host.
•  

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3. Anemia cont.

• Blood loss is associated with ____________________
  _____________________
• _________________________________________
• Infected adults become tired and rundown
• Mental and physical retardation commonly occurs
  in children.
• Recent findings indicate that there is a
  reduction in gamma globulins which results in
  _____________________________ to other
  infections.
• Combination of these factors can be fatal.

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Diagnosis
DIAGNOSIS - identify the eggs in the feces All
hookworm eggs look the same so cant ID
species Eggs are ovoid with thin, smooth
eggshell. Internally, eggs are always early in
mitosis - contain 2 to 16 cells. Size 55-75 µm
x 35-40 µm
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Treatment and Prevention
TREATMENT - ______________________________ is
effective in treating both species PREVENTION 1
. ___________________________________ - stop
pollution of soil with infected feces - this
has eliminated much of the problem in southern
U.S. 2. ___________________________________ -
prevent penetration of L3
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Dog and Cat Hookworms
Dog hookworm - Ancylostoma caninum - is easily
recognized by its 3 pairs of teeth in the buccal
capsule. Cat hookworm - Ancylostoma braziliense -
has a pair of long teeth.
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Dog and Cat Hookworms
Both species inhabit the small intestine of their
hosts. Life cycles and pathology are similar to
human species. HUMANS may serve as accidental
hosts of these hookworms when the
filariform larvae (L3) penetrate human skin.
L3 penetrates human skin
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2 Pathological Problems in Humans
1. __________________________________________(
Creeping Eruption) L3 of dog or cat hookworms
enter human skin and wander about in epidermis L3
are unable to penetrate into the dermis and are
eventually killed by our immune system Wandering
L3 cause a red, itchy irritation Treated with
thiabendazole ointment Present in the U.S.
another reason to clean up dog and cat feces!
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2 Pathological Problems in Humans
2. _______________________caused by Ancylostoma
caninum Recent finding only in ___________________
_- over 200 cases reported A few L3 are able to
penetrate skin to enter circulation and are
carried to small intestine. Cause severe swelling
and bleeding in region of small intestine where
they attach (called enteritis). Method of
Infection Dog defecates on lawn and then person
mows lawn barefooted and L3 penetrate
skin. Probably just a matter of time before cases

appear in the U.S.
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Rhabditid Nematodes - Chapter 24Strongyloides
stercoralis
This tiny nematode occurs in the small intestine
of _______________________________________________
____   Parasite is cosmopolitan in distribution
but is most common in warm, moist climates.
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• Only ____________________________ occur as
  parasites in the small intestine of their hosts.
• These worms are very small only 2 mm in length.
• Recognized by their elongate esophagus and
  single row of eggs within the uterus.
• Both males and females are found in part of the
  life cycle as free-living soil organisms.

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Life Cycle of Strongyloides stercoralis
LIFE CYCLE involves the ability to undergo either
a free-living existence or a parasitic existence
depending on conditions.
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Life Cycle of Strongyloides stercoralis

• 1. Parasitic female lives in the small intestine
  of humans and other mammals.
• - Females produce eggs by ________________________
  __- unfertilized eggs give rise to offspring.
• Parasitic females burrow into the mucosa to
  release their ova.
• 2. By the time the eggs reach the lumen of the
  small intestine, the eggs hatch and the ______ (
  rhabditiform larvae) are released into the lumen.

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Life Cycle of Strongyloides stercoralis
3. At this point, there are 3 possible pathways
that can be followed in the life cycle (1)
_______________________ - L1 molt twice to the L3
stage ( filariform larvae) as they pass through
the large intestine. They penetrate the wall of
the large intestine, enter the
circulation, migrate through the lungs, enter
respiratory tree, and are swallowed. Larvae
molt twice in small intestine and become
parasitic females.
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Life Cycle of Strongyloides stercoralis
(2) _______________________ - L1 are passed in
the feces onto warm, moist soil. In the soil, the
L1 molt 2x to L3 (filariform larvae) L3 penetrate
the skin (like hookworm larvae) and enter the
circulation. Go through lung migration, are
swallowed, and molt to parasitic females in the
small intestine.
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Life Cycle of Strongyloides stercoralis
(3) ________________________ - L1 rhabditiform
larvae are passed in the feces and
develop directly into free-living males and
females. These adults copulate and eggs
are released in the soil. L1 (rhabditiform
larvae) hatch from the eggs and may again
develop into free-living adults - OR - may
instead molt 2x to become
infective L3 that penetrate skin to start a new
parasitic cycle.
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Pathology of Strongyloides stercoralis
Infection is long-lasting (up to 40 years in WWII
POW's) and is generally
asymptomatic. 3 stages of pathology
1. ______________________________- skin
penetration of L3 - cause itching and
reddening of skin at penetration sites
2. ______________________________ - due to
lung migration of L3 - pneumonia-like
symptoms similar to Ascaris hookworms  
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Pathology of Strongyloides stercoralis
3. _____________________________________________
_ - parasitic females burrow into the mucosa and
submucosa of the small intestine causing
ulceration of tissue and sloughing of intestinal
cells.   - ulceration causes secondary bacterial
infections
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Pathology of Strongyloides stercoralis

• Small intestinal damage in immunocompetent
  persons causes intestinal pain
•  
• AIDS patients
• (this is the only helminth that causes greater
  pathology in AIDS patients)

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Strongyloides stercoralis
DIAGNOSIS (1) (2)
TREATMENT - __________________________________
is the drug of choice but has serious side
effects  PREVENTION -