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MLSMTAP3 : PARASITOLOGY
3RD TERM I A
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TOPIC : NEMATODES (SOIL TRANSMITTED HELMINTHES, EXTRA INTESTINAL)

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OUTLINE
Ascaris lumbricoides
Trichuris trichiura
Strongyloides Stercoralis
Hookworms
Enterobius vermicularis
Capillaria philippinensis
Trichinella spiralis
Dracunculus medinensis
Angiostrongylus Cantonensis

SOIL TRANSMITTED HELMINTHES
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Require further development in the soil before they become
infective
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Ex
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lumbricoides, T
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Stercoralis

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ASCARIS LUMBRICOIDES
Most common and largest intestinal nematode of man
Giant intestinal roundworm
The distribution of parasite is cosmopolitan
Ascariasis – occurs most frequently in tropical and subtropical
regions and estimated to infect 1
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Vitelline membrane – an inner non-permeable,
lipoidal layer
2
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Albuminous/mammillary coat – outermost layer
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Decorticated – mammillary coat maybe absent or removed
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Corticated – with albuminous layer
DX stage – fertilized and unfertilized ova
Inf stage – embryonated eggs

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PATHOLOGY AND CLINICAL MANIFESTATIONS
PATHOLOGY DUE TO LARVAL MIGRATION
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Initial pathological lesion → migrating larvae
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Pneumonitis resembling an asthmatic attack accompanied
by marked eosinophilia
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Loeffler’s syndrome – ascaris pneumonitis
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The severity of lesion depends on – sensitivity of the host,
nutritional status of the host, number of migrating larvae
PATHOLOGY DUE TO ADULT WORM
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Produce various pathological lesions
a
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Sporiative action – adult worms affect the nutritional
status of the host by robbing off its nutrition → can lead
to malnutrition and retardation of growth and
development
c
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Worms are still immature in the lumen
b
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Infection with only male ascaris worm
d
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develops in the soil within
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Well developed buccal
5 days
capsules characterized by
Non-feeding stage
the presence of semi-lunar Longer and slender with a
cutting plates
pointed posterior end
The mouth closes, the
esophagus elongates, and
the old cuticle remain as a
sheath covering the larva
OVA
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Ovoidal thin-shelled and colorless
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4-8 celled stage (in feces)
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Embryo may already develop inside the shell (in constipated
stool)
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Differentiation of necator egg from Ancylostoma egg is
difficult and impractical
Dx stage – ova in feces
Inf stage – filariform larva
ANCYLOSTOMA DUODENALE
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2 pairs of ventral teeth in buccal capsules of adult hookworm
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Body contour tends to follow the general curvature of the body
hence looking like a letter C

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Treatment – albendazole, mebendazole, pyrantel pamoate
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EPIDEMIOLOGY
The prevalence of trichuriasis in the Philippines ranges from 8090% and usually parallels that of ascariasis
Most infections are light to moderate and seldom produce
clinical symptoms

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PATHOLOGY AND CLINICAL MANIFESTATIONS
Pathology due to the larval stage
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Ground itch or coolie/dew itch
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Pulmonary lesion or Wakana disease
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Creeping eruption or cutaneous larva migrans
Pathology due to adult worms
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Hookworm anemia
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Hypoalbuminemia
DIAGNOSIS
Hookworm infection is diagnosed by the recovery of eggs on the
stool examination using

MEDICAL TECHNOLOGY ASSESSMENT PROGRAM 3 / GROUP B

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DFS
Kato-Katz technique
Concentration technique
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Formalin – ether concentration technique
Harada Mori (culture method) – use to differentiate rhabditiform
larvae from those of S
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Stercoralis are classified as
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Pulmonary infection
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Invasion of the skin by filariform larvae
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Penetration of the intestinal mucosa by adult female worm

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EPIDEMIOLOGY
5-45% - prevalence of hookworm in the Philippines depending
on geographic location and type of rainfall
Sandy loam – favorable for the infection
Human hookworm infection is greater in agricultural areas
96% hookworm infection – necator americanus
2% - Ancylostoma and 2% are mixed infection
Factors that contribute to the transmission of hookworms
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Mode and extent of fecal pollution of the soil
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Outer – thick hyaline
albuminous layer
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Cutting nails short
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Washing the bed linens and night dress
CAPILLARIA PHILIPPINENSIS

1st recognized in the Philippines in 1963 when first human case
dies of the disease in the PGH
1967 – epidemic of capillariasis took place in Pudoc west,
tagudin, ilocos sur (approx
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6 at birth
ANTERIOR END
Small orbicular, non•
Matured encysted larvae
papillated mouth
have digestive tract
Anterior fifth has a single
although the reproductive
ovary with vulva and long
are not fully developed
narrow digestive system
(female)
POSTERIOR END
Female – bluntly rounded,
3
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50 by
0
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50mm by 0
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In severe cases, there may be splenomegaly,
gastric and intestinal hemorrhages
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Encystment and encapsulation – the convalescent stage
wherein fever, weakness, pain, and other symptoms start to
disappear, full recovery is expected since trichinosis is selflimiting disease

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TREATMENT AND DIAGNOSIS
DIAGNOSIS
TREATMENT
Muscle biopsy –
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Thiabendazole maybe
demonstration of the
given during the 1st week
encysted larvae
of infection to expel adult
worm from the GI tract but
Serological test – CFT,
has no effect on migrating
ELISA, BFT (bentonite
larvae
flocculation test),
Bachmann intradermal test •
Mebendazole
using antigen
Beck’s Xenodiagnosis –
make use of experimental
animals like albino rats
EPIDEMIOLOGY, PREVENTION AND CONTROL
EPIDEMIOLOGY
PREVENTION AND
CONTROL
Common in pork-eating
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Food sanitation
countries
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Recommended that meat
Strictly zoonosis
be cooked at 77C (177F)
Final and intermediate
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Freezing – another way to
hosts are required to
kill larvae, storage at -15C
complete the life cycle
for 20 days or -30C for 6
days is effective

ANGIOSTRONGYLUS CANTONENSIS
Rat lungworm, rodent lungworm
Habitat – lungs of rat (pulmonary arteries)
Disease – angiostrongloidiasis or eosinophilic
meningoencephalitis in man

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DRACUNCULUS MEDINENSIS
Guinea worm, medina worm, dragon worm, fiery serpent worm
of Israelites
Disease – dracunculiasis or dracontiasis
Habitat – subcutaneous tissues of man usually the foot or lower
limb
Ancient disease
Longest nematode – reaches 1 meter
Russian biologist Fedtschenko 1870 – discovered the role of
cyclops as vector in transmission of disease

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MORPHOLOGY
ADULT
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Male
Difficult to demonstrate as
they die immediately after
fertilizing the female
FEMALE (VIVIPAROUS)
Milky white, slender and
looks like a thick twine of
thread
Rounded anterior end and
tapering posterior end in a
form of hook-like structure
Minute triangular mouth in
anterior end

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LARVA
1ST STAGE LARVA
Unsheathed and coiled
with round anterior end
and a long slender
filariform tail
Tadpole-like movement in
water
Short life unless taken up
by cyclops
INFECTIVE STAGE (L3)
3rd stage larva found in the
body cavity of cyclops

MEDICAL TECHNOLOGY ASSESSMENT PROGRAM 3 / GROUP B

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Pair of uteri, oviducts,
Vector – cyclops (Mesocyclops
tubules, single unpaired
leuckarti, M
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The worm in often visible in opening
of the ulcer
RESERVOIR, SOURCE, MOT
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Man – only reservoir of infection
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water contaminated with cyclops – main source of infection
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man acquires infection by drinking water contaminated with
cyclops harboring L3
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the condition is essentially a disease of rural poor people
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DIAGNOSIS
PARASITIC DIAGNOSIS
established by observation
of the typical ulcer and
flooding ulcer with water to
recover the discharge
larvae
SERODIAGNOSIS – IFA,
IHA, ELISA, western blot
IMAGING METHODS –
radiologic examination of
the affected part
demonstrates dead and
calcified parasites

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TREATMENT
Slowly wrapping the worm
on the stick (ancient
method and used in many
endemic area)
Surgical removal
Niridazole – preferred
Metronidazole,
thiabendazole – alternative
Anti-inflammatory drugs
and antibiotics provide
relief from 2nd bacterial
infections

MEDICAL TECHNOLOGY ASSESSMENT PROGRAM 3 / GROUP B

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