Saint Louis University
School of Medicine
PARASITOLOGY
I. Ancylostoma duodenale
M.03 THE STRONGyLIDA: Hookworms
Dr. Ayochok | October 1, 2019
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Aka “Old world hookworm”
A. MORPHOLOGY
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Adults: stout, cylindroidal/cylindrical, slightly constricted
anteriorly, with prominent cervical curvature
Pinkish or creamy gray
Tough cuticle
A pair of lateral cervical papillae behind or just
below the circumesophageal nerve ring
OUTLINE
INTRODUCTION
I.
Ancylostoma duodenale
a. MORPHOLOGY
b. LIFE CYCLE
II.
Ancylostome ceylanicum
III.
Ancylostoma braziliense
IV.
Ancylostoma caninum
V.
Necator americanus
a. MORPHOLOGY
b. LIFE CYCLE
VI.
HOOKWORM INFECTION AND DISEASE\
a. Epidemiology
b. Cutaneous Lesions
c. Cutaneous Larva Migrans
d. Pulmonary Lesions
e. Intestinal Infection
VII.
DIAGNOSIS
VIII.
TREATMENT
IX.
PREVENTION AND CONTROL
INTRODUCTION
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Order: Strongylida
Common features:
1. Female: complex ovijector, sphincter well-developed
2. Male: caudal bursa, pair of spicules
3. Claviform esophagus
4. H-shaped excretory system
5. Stoma is either without lips, with 6 lips, or with corona
radiate
Aka “Bursate nematodes” (Phasmid)
All hookworms have the meromyarian type
of somatic muscle with two to five cells arranged
per dorsal or ventral half.
Geohelminths/ soil – transmitted helminths
4 Superfamilies:
1. Ancylostomaloidea:
a. Ancylostoma duodenale
b. Ancylostoma ceylanicum
c. Necator americanus
2. Stronglyloidea
3. Trichostrongyloidea
4. Metastrongyloidea
Males:
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8-11 mm long x 0.4-0.5 mm
Prominent cervical curvature appreciated
Posterior body extended into campanulate bursa
supported by fleshy rays
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The number of the fleshy rays, the size as well as
the length is specific for the genus and species
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2 copulatory spicules, not fused on their end
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Retracted copulatory spicules inside
2 most common hookworms of man:
Ancylostoma duodenale
Necator americanus
Ventral cutting teeth
Development in lungs of final
host is not essential
Ventral cutting plates
Larval development in lungs is
essential
A.
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More common hookworm in the
Philippines
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local studies on speciation of human hookworms
revealed that out of 1,958 samples positive for
hookworm in cultures, 97% were identified as N.
americanus, 1% as A. duodenale, and 2% were
mixed infections
PARASITOLOGY
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Duodenale male bursa
1 testis proceeds anteriad, winds back and forth, turns
posteriad as a tubule
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Coiled testis will expand as seminal vesicle,
then as muscular ejaculatory duct
1 pair of bristle-like copulatory spicules regulated by
muscles
These can already be seen by the naked eye
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
PARASITOLOGY
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Females:
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10-13 mm long x 0.6 mm
Identifying feature: Conoid posterior end with
subterminal anal opening
Vulva is midventral
2 ovaries (1 anterior, 1 posterior) continuous at distal
ends with the two oviducts à seminal receptacle à
uterus
To muscular overjector, to transverse vagina to vulva
Slightly longer than their male counterpart
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Egg of hookworm
B. LIFE CYCLE
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Buccal capsule:
The orientation of the different structures particularly
the teeth is very helpful in identifying a particular
hookworm
Outer articulated portion and an inner fused portion
Ventral (upper): 2 fused teeth:
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Outer tooth larger
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Inner tooth with median process
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Diagnostic/pathognomonic of A.
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Excretory System:
the flame cell has its counterpart in hookworms called
“carrying cell”, “suspensory cell”, which leads to a
pair of tubules from buccal capsule to subcaudal area.
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Drain to excretory canals then to a common
excretory canal/ a rudimentary bladder
Eggs:
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Eggs of all hookworms appear similar, we cannot
identify a particular hookworm based on the
morphology of the egg
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Report: Presence of hookworm egg/s
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Hookworms are oviparous parasites
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Formed in ovaries
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Vitelline membrane and shell added from uterine
wall
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Fertilized as they pass thru seminal receptacle,
discharged in lumen of intestine
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Daily output: 25,000 to 30,000
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Appearance is similar to eggs of Strongyloides
Free living phase: Rhabditiform larvae
Discharged egg in early cleavage stages
Eggs are fully embryonated in moist, shady, warm,
sandy loam
Hatch in 1-2 days to release Rhabditiform larva
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Long narrow buccal chamber, flask-shaped
esophagus, inconspicuous genital primordium,
molts once
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Diagnostic stage
5-8 days: filariform larva: viable in moist soil for
weeks
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Infective stage
duodenale
Dorsal (lower): dental plate with median cleft
PARASITOLOGY
2 of 7
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
PARASITOLOGY
RHABDITIFORM
Hookworm
Short
Long
Large/conspicuous Small/inconspicuous
II. Ancylostoma ceylanicum
Strongyloides
Buccal Cavity
Genital
Primordium
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FILARIFORM (L3 Stage)
Hookworm
Long
Short, flask-shaped
Notched
Pointed
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Strongyloides
Esophagus
Tail
FILARIFORM COMPARISON
Males: 8 mm long
In comparison with A. duodenale:
Bursa broader
Lateral rays more curved
Females: 10 mm long
Buccal capsule:
Teeth with ” (quotation) configuration
Anterior edge of mouth capsule: on each side is one
large tooth and below (behind) is a very small tooth
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The large tooth is the one obvious during
microscopic observation
Ancylostoma ceylanicum buccal capsule
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Parasitic phase:
Filariform larva penetrates skin to subcutaneous
tissues
Via the blood vessels , gets carried to the lungs, up to
the respiratory tree (with no essential development;
not essential for it complete its development), down
the GIT, molts again: mature worms
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Optional for Hookworm
Develop into mature worms without passage thru the
lungs: filariform larva can still mature when
swallowed
5 weeks: exposure to oviposition
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Oviposition: females are already releasing eggs
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No parthenogenesis
PARASITOLOGY
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Typically occurs in cats
Cat Hookworm
Common in Southeast Asia
Dogs and man: intestinal infection
Does not cause cutaneous larva migrans in man
III. Ancylostoma braziliense
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Males: 8 mm
Bursa is square shaped, as broad as long
Short lateral rays
Females: 8 mm
Angular bend at the level of the vulva (blue arrow)
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Unique for this species
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
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PARASITOLOGY
Buccal capsule:
A pair of inconspicuous median teeth (red arrow)
A pair of larger outer teeth (blue arrow)
Collectively, two ventral pairs of unfused teeth
B. MORPHOLOGY
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Males: 7-9 mm long x 0.3 mm
Bursa long and wide, spicules long, slender and
fused at the tip, forming a barb (blue arrow)
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Females:
9-11 mm long x 0.4 mm
Vulva middle or anterior; paired organs
Eggs:
longer and more elongated than those of A. duodenale
Shell very thin, disorganized mass inside
In wild and domesticated feline and canine hosts
Tropics, subtropics
Produces cutaneous larva migrans in man
IV. Ancylostoma caninum
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Dog Hookworm
Males: 10 mm long
Bursa with moderately slender rays
Females: 14 mm long
Buccal Capsule: 3 pairs of ventral teeth (blue arrows)
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C. LIFE CYCLE
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Adults: jejunum, ileum attached to mucosa
Detachment for movement from time to time for
feeding and mating
Requires pulmonary migration with essential
development in the lungs (3rd stage larva) before
maturity in the intestine
Light infections: 100-500 eggs/female/gm of feces
Note: N. americanus follows the direct life cycle of Strongyloides
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Eggs: same but larger than those of A. duodenale
Common parasite of dogs
Causes creeping eruption
Can invade skeletal muscle fibers
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“American Hookworm”
“American Murderer”
Adults: attenuated anteriorly
Strongly flexed dorsalward at the anterior end
Grayish-yellow, sometimes reddish
Small buccal capsule:
ventral (upper) (blue arrow) and dorsal (lower) pair of
semilunar cutting plates
Subventral and subdorsal lancets
Amphidial, excretory, esophageal glands: exodigestive,
antigcoagulant (amphidial)
stercoralis – requires a host for its life cycle. Autoinfection is only
manifested by Capillaria philippinensis and Strongyloides
VI. HOOKWORM INFECTION AND DISEASE
A. EPIDEMIOLOGY
V. Necator americanus
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PARASITOLOGY
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Endemicity dependent on:
1. Continuous presence of human infections
2. Defecation habits ensuring eggs are deposited in
favorable locations for extrinsic development of parasite
3. Appropriate environmental conditions (shade and sandy
humus)
4. Opportunity for filariform stage to penetrate skin
Temperature: major factor affecting geographic distribution
and prevalence
Necator americanus – high temperature (tolerant)
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Reason why they are common in the philippines
Ancylostoma : low temperature
Pattern of rainfall:
Dampness, condensation: infective larvae migrate to soil
surface – ready to penetrate skin
Dryness: larva retreat and wait for the perfect
opportunity to penetrate a host
Dung beetles: form soil-feces matrix
Favors larval development
Philippines: Necator americanus is a more serious concern
Suitability of the environment for eggs or larvae:
damp, sandy, friable soil (24-32 °C)
Fecal pollution in soil
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Promiscuous defecation
Extent of contact between infected soil and skin or
mouth
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
PARASITOLOGY
B. CUTANEOUS LESIONS
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E. INTESTINAL INFECTION
Brought about by the Filariform larva
Site of entry: itching sensation
“Ground itch”: pruritis, erythema, papular
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Aka Dew itch: contact with soil on a dewy
morning
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Depends on how sensitized the host is
May become vesicular
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Depends on how you scratch
Papulovesicular eruptions can last for two weeks
Secondary bacterial infection
Abrasions due to scratching
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Attach to intestinal mucosa
Temporary head, then permanent head
Digest portions of villi
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Blood sucked out of the tissues
Greater amount of blood lost thru bleeding at sites of
attachment
Bleeding ceases shortly after worm leaves site
Acute, heavy hookworm infection:
Fatigue, nausea and vomiting, diarrhea (black to red),
steatorrhea, weakness, pallor, burning/cramping
abdominal pain
Massive intestinal hemorrhage: very heavy infections
Eosinophilic leukocytosis, Charcot-Leyden crystals in
feces
More in A. duodenale
Chronic: Iron Deficiency Anemia
Pallor, facial/pedal edema, enlarged heart
Mental/Physical retardation
“Hookworm disease”: Microcytic, hypochromic anemia
(intestinal)
NOTE: Hookworm infection vs disease: somebody has a
disease when the patient manifests already with
microcytic, hypochromic anemia, otherwise it is only
an infection
Hypoalbuminemia
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Low level of albumin due to combined loss of
blood, lymph and protein
Clinical severity: worm burden
<5 eggs/mg feces
>20 eggs/mg: Significant anemia
>50 eggs/mg: massive
Nutrition: can prevent progression or development of
hookworm disease if infection is light/moderate
Heavy infection: adequate absorption is not possible
Threshold component: bleeding from multiple areas of
laceration as well as reattachment
Compensations:
Increased pulmonary vital capacity
Increased tolerance to anoxia
Decreased systolic pressure
Decreased peripheral blood flow
Increased collateral circulation
Prognosis of hookworm infection is good in general
C. CUTANEOUS LARVA MIGRANS
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Aka: Creeping eruption
A. braziliense: most common cause
Also: A. caninum, N. americanus
Itching papules, serpiginous tunnels
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Follows the track of the filariform larvae
Red, then becomes elevated and vesicular
Larval movement: several mm/day
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Pruritis: scratching à pyogenic infection
Migration: continues for weeks or months
Larvae of A. braziliense/caninum
Able to infect by mouth
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When the filariform larva is swallowed
Can migrate to deeper tissues
When extensive: followed by pneumonitis: larvae,
eosinophils, Charcot-Leyden crystals in sputum
Can invade other areas of the body like the cornea
Infections acquired via:
Contact with moist or wet sandy or sandy-loam soil
containing filariform larvae from dogs and cats
Unprotected sandboxes
Bathing beaches
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This is when you let your cats and dogs poop in
the sand
Under houses with leaky pipes
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D. PULMONARY LESIONS
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Wakana disease
Syndrome caused by migrating larvae
Initial: Nausea, vomiting, salivation, pharyngeal itch,
hoarseness
After several days: Cough, dyspnea,
hypereosinophilia, chest X-ray infiltrates
Allergic reaction to larvae
Characteristic of Necator as it requires pulmonary
migration
Minute focal hemorrhages in alveoli
Pneumonitis
Massive larval migration
Typical: no high degree of sensitization characteristic
of Ascaris or Strongyloides
PARASITOLOGY
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5 of 7
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
PARASITOLOGY
VII. DIAGNOSIS
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IX. PREVENTION AND CONTROL
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Creeping eruption:
inspect lesions, history of exposure
Hookworm disease
hookworm eggs demonstrated in stool, decreased
hemoglobin
Threshold level:
20 eggs/mg (well nourished)
5 eggs/mg (iron or protein deficiency)
Stored feces (>24 hours):
Rhabditiform larvae
Direct Fecal Smear
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Only of value when the infection is heavy
Kato Thick or Kato Katz Method
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Increase detection rates since more stool are
examined using these techniques
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Kato Katz provides quantitative diagnosis by
determining the intensity of infection in terms of
number of helminth eggs per gram of feces
Zinc sulfate centrifugal floatation and formalin –
ether/ ethyl acetate concentration method
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Contributes to increase in sensitivity
FLOTAC
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Higher sensitivity than Kato Katz Method
Harada Mori Culture method
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Allows hatching of larvae from eggs on strips of
filter paper with one end immersed in water
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CHECKPOINT
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Creeping eruptions:
Thiabendazole
Manual removal of larvae
Supportive/Symptomatic:
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Antihistamines
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Antipruritics
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Sedatives
Albendazole 400 mg PO SD
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For the scattered treatment of a hookworm
infection
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Drug of choice and is larvicidal and ovicidal
Mebendazole 100 mg PO BID x 3 days or 500 mg PO
SD
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Block uptake of glucose by most intestinal and
tissue nematodes
Pyrantel pamoate: 11 mg/kg (max 1 gm) PO OD x 3 days
Wakana disease: adrenocorticosteroids
Anemia and hypoproteinemia should also be addressed by
giving iron supplementation and adequate diet
PARASITOLOGY
1.Cause cutaneous larva migrans, except:
a.Ancylostoma braziliense
b.Ancylostoma caninum
c. Ancylostoma ceylanicum
d. Necator americanus
2. T/F: Necator americanus has a quotation mark configuration of
buccal capsule; bursa is broader than A. duodenale; fleshy rays
are more curved compared to A. duodenale
1.F- 2.A - 3.F – 4.B – 5. F – 6. C – 7. C – 8. D – 9. E – 10. E
1.C – 2. F-A. ceylanicum
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Ancylostoma duodenale
Ancylostoma ceynalicum
Ancylostoma braziliense
Ancylostoma caninum
Necator americanus
All of the above
1.Order Strongylida
2.Two fused teeth – ventral; dental plate with media cleft – dorsal
3. Oviparous
4. typically occur in cats
5.Suspensory cell/carrying cell
6. Angular bend somewhere at the level of vulva
7. One pair of inconspicuous median teeth, pair of larger outer
teeth
8. 3 pairs of ventral teeth
9. Cutting plates
10. male bursa is fused at the tip forming a barb
VIII. TREATMENT
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Sanitary disposal of human feces
Construction and proper maintenance of latrines
Treatment of egg passers
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To control hookworm disease
Creeping eruption:
Covering sandboxes
No dogs or cats in bathing beaches
Wearing of shoes, slippers and boots
Health education on personal, family, and community
hygiene
Mass chemotherapy when prevalence is more than 50%
6 of 7
[GAPUZ, MACATIAG]
Saint Louis University
School of Medicine
PARASITOLOGY
PARASITOLOGY
1 of 7
[GAPUZ, MACATIAG]