1. CHAPTER THREE
HELMINTHS
4/3/2023 1

2. 4/3/2023 2
At the end of this class the students will be able to:
• Define helminths
• Describe the general features of helminths
• Describe the taxonomic classification of
helminths
Learning objective

3. Outlines
• Introduction to helminths
• General features of helminths
• classification of helminths
4/3/2023 3

4. 3.1. Introduction to Helminths
Medical Helminthology: study of these parasitic worms
and their medical consequence
Helminths: derived from the Greek word
“helminths” or “helminthose” meaning worm
4/3/2023 4

5. 3.2.General features of helminths
Higher, multicellular forms with specialized organs
Adult worms vary in size (6mm->10m)
Their life cycles may be simple or complex
Pathology, clinical sign and symptoms:
Depend on the location of the organisms
 May be caused by adults, larva, or egg
 Laboratory diagnosis mainly depends on
 Detection and identification of egg , larva or
embryo and rarely adults
4/3/2023 5

6. 4/3/2023 6
Larvae: Nematodes Cestodes Termatodes
Larvae: various larval forms found in man and other hosts.
Rhubiditi form
larva
Filari form larva
Microfilaria
Cysticercus
Cysticercoids
Coenurus
Caracidium
Plerocercoid
Hydatid cyst
Miracidium
Sporocyst
Radia
Cercaria
Metacercaria
Morphology
Adult: -
 Most are macroscopic and visible to the naked eye

7. General features...
 Egg (ova):- with few exceptions all helminths produce
egg when pass out in different excretion.
 Differentiated based up on their
– size, color, shape, shell and contents.
 Life Cycle: - may be completed in one or more than one
host.
 Mode of transmission:- can be direct or indirect
4/3/2023 7

8. HELMINTHES
NEMATHELMINTHES
(NEMATODES)
PLATYHELMINTHES
TREMATODES CESTODES
Classification of helminths
4/3/2023 8

9. 4. Nemathelminths
4/3/2023 9

10. Learning objective
At the end of this sub-section the students will be able
to:
• Describe the general epidemiological aspects of
nemathelminths
• Discuss the characteristics of each nematode
• Explain the life cycle of each nematode
• Apply the necessary laboratory procedures for the
detection and identification of nematodes
4/3/2023 10

11. Outlines
• General features of Nemathelminths
• Burden and impact on human life
• Classification of nemathelminths
• Intestinal nematodes
–General features
–For each species:
 Epidemiology , morphology, transmission life
cycle , clinical features, laboratory diagnosis
treatment, prevention& control
4/3/2023 11

12. 4.1. General features of
Nemathelminths
• Round in cross-section
• Unsegmented
• Most intestinal species are
soil transmitted
• Digestive system complete
 Possess mouth, oesophagus and anus
• Have separate sexes
4/3/2023 12

13. Females are either:
oviparous/ovoviviporous/viviparous
– Egg (ova) -Larva(L1-L4)-Adult
Possess a shiny cuticle (smooth/spined/ridged)
Mouth is surrounded by lips or papillae
Complete the life cycle in a single host except the
super families
Filariodea and Draconculoidea
General features...
4/3/2023 13

14. General features...
• The core nematode life cycle involves development from
an egg through five stage of growth
• The first four stages known as larval stages and referred
to as L1,L2,L3 and L4
• The fifth and final stage of development is asexually
mature adult worm
4/3/2023 14

15. • Have Four larval stages
4/3/2023 15

16. • ≈ 500,000 spp. globally
• Most are free
living
• Abundant pathogens in
life-stock and pets
• Important pests of many
crops
• Cause numerous human
diseases
4.2. Burden and impact on human life
4/3/2023 16

17. •The warm regions of the world = worm regions.
•High burden
•In the rural villages
•unsanitary overcrowded cities
•'big three' (Ascaris, Trichuris & Hookworm) is common
•Temperate and cold climates are not spared.
4/3/2023 17

18. 4.3. Classification of Nemathelminths
• INTESTINE NEMATODE
• Small intestine
– Ascaris lumbricoides
– Hook worm
– Strongyloides
stercoralis
• Large intestine
– Trichuris trichuria
– Enterobius
vermicularis
• BLOOD & TISSUE
NEMATODE
• Adults or larval stage in tissue
• Filaria –
– Wuchereria bancrofti
– Brugia malayi
– Onchocerca volvulus
– Loa loa
• Trichinella spiralis,
• Draconculus medinensis
4/3/2023 18

19. Cont…
4/3/2023 19

20. 4.4. INTESTINAL NEMATODES
General features
• Live in gastro-intestinal tract
• In humans, often spread by poor hygiene related to
feces
• Most species are geo-helminths (soil transmited)
• Female worms are oviparous
• Humans are the only or major host of intestinal
nematode
4/3/2023 21

21. Transmission:
– Ingestion of infective egg
– Larva penetrating skin
There are usually only two sites of entry for intestinal nematodes
infecting humans
The mouth and the skin
Ingestion of eggs or in some cases L3 larvae result infections
Eggs may be ingested inadequately washed ,uncooked vegetables
and L3 larvae may be ingested in contaminated water.
L3 larvae of Hook worm have capacity of penetrating intact skin.
4/3/2023 22

22. Laboratory diagnosis:
– Egg in faeces ( most often)
– Larva in faeces
– Recovering egg in the skin around the anus
– Occasional adult worms: A. lumricoudes, E.
vermicularies
4/3/2023 23

23. Cont...
It includes
• Ascaris lumbricoides
• Trichuris trichiura
• Enterobius vermicularis
• Strongyloides stercoralis
• Ancylostoma duodenale
• Nectator amircanus
Before becoming adults in their human host, the larvae of
A. lumbricoides, S. stercoralis , and hookworms have
heart lung migration
4/3/2023 24

24. 4.4.1. Ascaris lumbricoides
 Also known as large intestinal round worm
 the first human helminth recorded in Chinese medical
literature(about 300-200 B.C.)
Epidemiology
 world wide
4/3/2023 25

25. 1.45 billion people are infected annually
WHO estimated it resulted in 60,000 persons death in
1995
4/3/2023 26

26. • In Ethiopia
–ranges from 17% to 77.7%
–Highest rate in school children (2/3rd)
–Distributions affected by altitude and climate
 29% in highlands,
35% in the temperate areas
 38% in the lowlands
4/3/2023 27

27. Habitat
Adult: In the small intestine
Egg: In the faeces
 extremely resistant to adverse
environmental condition and
chemicals
 remains viable in soil and dust
for up to 10 years
4/3/2023 28

28. Morphology
Adult: colour pinkish, cylindrical
with tapering end
Male: Size: about 15cm
curved tail two
copulatory spicules
Female: size 2-25cm , with a straight
tail
The female has a lifespan of 1 – 2
years and is capable of producing 200 000 eggs per day !!
4/3/2023 29

29. Transmission and Life Cycle
Transmission
• A. lumbricoides is spread by faecal pollution of soil
• Infective stage:- egg containing 2nd stage larva
A person acquire infection by
1. Ingestion of food or water contaminated with infective
eggs
2. Eating soil(geophge) frequently seen in children
3. putting contaminated finger or toys with infective egg
in to mouth
4. rarely by inhalation of eggs carried in air
4/3/2023 30

30. The infection is common in areas with
 high density of human population
Poor sanitation
Habit of people to defecate indiscriminately in
and around settlements
Use of infected faeces as fertilizer
4/3/2023 31

31. Life cycle
• Fully embryonated eggs are swallowed & L2 hatches
in the stomach & penetrate stomach or duodenal
mucosa
• L2 enter blood stream & leave through alveoli into lung
• Then molt several times in the lungs to L3/L4
• Then move up and get swallowed
4/3/2023 32

32. Life cycle...
• 2-3 months after infection the adult worms start laying
eggs (200,000 daily)
• Eggs are shed with the feces and embryonate within 2-3
weeks
4/3/2023 33

33. Life cycle...
4/3/2023 34

34. Pathogenesis:
1. “Verminous” pneumonia, lung tissue damage due to
migratory larvae.
2. Bowel obstruction - too many adult worms.
3. Parasite secretes trypsin inhibitor, prevents host
from digesting proteins.
4. Aberrant migration of “irritated” adult worms to:
a. Common duct
b. Liver
c. Pharynx
d. Peritoneum
4/3/2023 35

35. 4/3/2023 36

36. Pathogenesis...
• With heavier worm
loads a tangled mass of
worms can obstruct the
bowel,
• an individual worm can
block a duct
4/3/2023 37

37. A. Finding and identification of eggs in the stool.
– Direct wet mount
• adequate for detecting moderate to heavy infections
– concentration technique may be used In light infection,
Sodium chloride floatation technique &
Formolo-ether concentration technique
B. Adult worms occasionally passed in the stool or through
the mouth or nose
C. Larvae can be identified in sputum or gastric aspirate
during the pulmonary
– migration phase (examine formalin-fixed organisms for
morphology
Laboratory Diagnosis
4/3/2023 38

38. The diagnostic form is the egg in feces.
Unmated females lay non fertilized eggs.
4/3/2023 39

39. 4/3/2023 40

40. 5 types of Ascaris eggs in stool
A.Fertilized Egg With Double Shell
– Size: about 70m
– Shape: oval, or some times round
– Shell: The two layer are distinct,
rough , brown, covered with little
lumps
– Colour: brown external shell, and the
contents are colorless or pale yellow.
– Content: a Single rounded granular
central mass.
4/3/2023 41

41. B. Unfertilized Egg With Double Shell
– size: 80-90m
– shape; more elongated
(elliptical)
– shell: brown, puffy external
shell and thin internal shell.
– content: full of large round very
refractile granules
4/3/2023 42

42. C. Semi-decorticated Fertilized Egg
o Similar to Type A but With out the
external Shell
o Shell: single , smooth, thick
and colourless or very pale
yellow.
o Content: a single rounded
colourless granular central
mass.
4/3/2023 43

43. D. Semi-Decorticated Unfertilized
Egg
– Shell: a single smooth thin
colourless shell (double line)
– Content: large rounded
colourless refractile granules.
4/3/2023 44

44. • E. Embryonated Egg
4/3/2023 45

45. Treatment
Mebendazole
Early operative intervation allowing the worms to be
milked toward colon before large worm burden
causes bowl obstraction.
Prevention and Control
1.Prevention of infection by
 washing hands before eating & trimming finger
Avoid eating uncooked foods such as vegetables
4/3/2023 46

46. 2. Preventing soil become faecally polluted by
» sanitary disposal of faeces in latrines
» avoiding the use of night soil as a fertilizer
3.Treatment and health education
• Mass de-worming programmes repeated at 3-6
month intervals, have been advocated in areas of
high prevalence
4/3/2023 47

47. 4.4.2.Trichuris trichiura
• Common name : whipworm, due to the whip-like
form of the body.
Epidimology
– The third most common round worm of humans
worldwide
– Infections more frequent in areas with tropical weather
and poor sanitation practices, and among children
4/3/2023 48

48. Epidimology...
– ~ 1.12 billion cases world-wide
– ~ 1.05 billion people are infected annually
In Ethiopia
One national survey showed 36.1%
On study in central and northern plateaus: mean
prevalence of 49%
4/3/2023 49

49. Habitat
Adult: large intestine (caecum) and appendix
Eggs : In the faeces, not infective when passed
Morphology
 Adults: whip-like shape, anterior 3/5th of the worm
resembles a whip & the posterior 2/5th are thick
Male : Size 30-45 mm , coiled tail
Female: 35-50mm, straight thick tail
4/3/2023 50

50. 4/3/2023 51

51. 4/3/2023 52
Egg:
Size: 50-54m
Shape: "tea tray eggs” or
barrel- shaped with a
colorless protruding mucoid
plug at each end
Shell: fairly thick and smooth,
with two layers & bile stained
Color: yellow brown
Content: a central granular mass
which is Unsegmented ovum

52. Transmission and life Cycle
Transmission
Ingestion of embryonated egg in contaminated
water , food or from contaminated hand
Life Cycle
• The unembryonated eggs are passed with the
stool of infected individuals
4/3/2023 53

53. Life Cycle
• Mature within three weeks of being deposited in
soil.
–require a warm, moist environment with plenty
of oxygen to ensure embryonation
–The embryonated eggs are extremely resistant
to environmental conditions
• When embryonated eggs are swallowed larvae are
released into the upper duodenum
• then attach themselves to the villi of small
intestine or invade the intestinal walls
4/3/2023 54

54. Life Cycle...
• After 3-10 days they move down to the caecum
& ascending colon where they mature into adult
worms
• The adult worms are fixed with the anterior
portions threaded into the mucosa
• The females begin oviposit 60 to 70 days after
infection& shed 3,000 - 20,000 eggs per day
• The life span of the adults is about 1 year
4/3/2023 55

55. 4/3/2023 56

56. 4/3/2023 57

57. Clinical features
• Are largely determined by the worm burden:
• The severity of symptoms is directly proportional to the
intensity of infection.
• < 10 worms are asymptomatic (99% asymptomatic)
• Patients who are well-nourished will be able to
tolerate small number of adult worms.
• Heavy worm burden
–Mechanical damage to the intestinal mucosa
–Chronic profuse mucus and bloody diarrhea with
abdominal pains and edematous prolapsed rectum
4/3/2023 58

58. Clinical features...
– Anaemia from blood loss and iron deficiency,
malnutrition, weight loss and sometimes death
–Each adult worm sucks about 0.005 ml of
blood per day
– Rarely a child will develop congestive cardiac
failure because of anaemia and fluid retension
hypoproteinemia and oedema
4/3/2023 59

59. Clinical features...
• The immature T. trichiura burries its entire body in
the epithelial of large intestine forming a tunnel.
• As the worm matures intimate contact of T. trichiura
with the mucosa of large intestine leads to
inflammation of mucosa
• The mucosa may be oedematous and friable
• The surface tissue of the rectum become extremely
oedematous and the patient strain to defecate rectal
prolapse may occur.
• Prolonged massive infection leads to iron deficiency
anemia
4/3/2023 60

60. 4/3/2023 61

61. 4/3/2023 62
Trichuris vulpes (dog whip worm in
the intestine of an infected dog

62. Laboratory diagnosis
4/3/2023 63
1.Finding of characteristics egg in faeces
2. Sigmoidoscopy may enable visualisation of worms
Treatment
Mebendazole
 Treat the iron deficiency anaemia
Prevention and Control : the same as described
for A. lumbricodes

63. 4.4.3. Enterobius vermicularls
Common name: “Pin Worm” or “threadworm” or “ seat
worm”
• Causative agent of enterobiosis (oxyuriosis)
– nematodes that is manifested by intense irritation of the
perianal region
Epidimology
occurs world-wide
Children (5-14 years ) are more commonly infected than
adults
Occur in group living together
4/3/2023 64

64. 4/3/2023 65
• Pinworms eggs can be
spread throughout a
house and difficult to
eliminate.
• Small children are
most apt to pick them
up during the
“teething stage.”

65. In Ethiopia :
5 % school children in rural communities in
Gonder region had
E. Vermicularis eggs under their finger nails
 only 0.5% of them were found to shed eggs in the
stool
 Recent studies done using routine stool examination
method, a prevalence rate up to 1% were reported
4/3/2023 66

66. Habitat
Adult: Caecum & appendix
Gravid female: Caecum & rectum
Eggs: deposited on perianal skin & occasionally in
faeces
 In severe infections, numerous living pinworms are often
shed in stool and are easily recognizable as motile
worms on the surface of the feces.
Morphology
 Adults: Color: yellow white
Male: Size 2-5mm Coiled tailed
Female: 8-13mm, thin pointed tail
4/3/2023 67

67. 4/3/2023 68
They are small white worms with pointed tail
swollen cuticle at anterior end prominent
esophageal end bulb
Morphology of Enterobius vermicularis adult
female

68. 4/3/2023 69
Egg
Size: 50-60m
Shape: oval but flattened
on one side, rounded
on the other side
Shell : Smooth and thin
but with double shell
Content: either a small
granular mass or a
small curved up larvae

69. 4/3/2023 70
50–60 x 20–32 μm

70. 4/3/2023 71

71. Transmission and Life cycle
4/3/2023 72
Transmission
Person –to- person transmission(ingestion and air
borne)
Eggs remains viable 20 days
• Autoinfection: occurs mainly by uptake of eggs that
are transmitted to the mouth with the fingers from
the anal region
• Retro infection: infective larvae would be released at
the anus to migrate back into the intestine.

72. Life cycle
• Ingestion embryonated eggs, usually carried on
fingernails, clothing, bedding or house-dust.
• Eggs hatch in stomach, larvae migrate to caecal
region where they mature into adults
• Copulation takes place in the caecum
• Gravid females migrate nocturnally outside the anus
and oviposit on the perianal area
• 1 pin worm lay over 10,000 -15,000 eggs /day
covered with a sticky proteinaceous layer enabling
them to adhere to the skin.
4/3/2023 73

73. Life cycle...
• Within 4-6 hours being laid the egg contain
infective larvae
• Perianal itching from the eggs
– Induces scratching and hence the eggs are
transmitted to the mouth on the fingers
• Retroinfection, or the migration of newly
hatched larvae from the anal skin back into the
rectum
• Interval from ingestion of infective eggs to
oviposition by the adult females is about one
month
4/3/2023 74

74. 4/3/2023 75

75. Clinical features
4/3/2023 76
 Nocturnal anal pruritis.
• The cause of this is unknown, but may be related to
the intensity of the infestation, and/or an allergic
reaction to parasite
 Sleeplessness, because of the irritation
 Vulvovaginitis, and even urethritis may occur in girls
when migrating worms lay their eggs in these sites
 Abdominal pain or appendicitis resulting from the worms
are considered to be very rare

76. 4/3/2023 77

77. 4/3/2023 78
Egg of E. vermicularis and scotch tape
preparation

78. Laboratory Diagnosis
4/3/2023 79
1.Finding eggs from perianal skin using adhesive tape or
swab method
o Done by pressing transparent adhesive tape ("Scotch
test", cellulose-tape slide test) on the perianal skin and
then examining the tape placed on a slide.
o Alternatively, anal swabs or "Swabe tubes" (a paddle
coated with adhesive material) can also be used.
o Collect sample in the morning, before defecation and
washing,

79. 4/3/2023 80
• The “Scotch Tape Test”
– place a piece of Scotch
Tape on the anal area.
– The tape is placed on a
slide and examined under
a microscope for the flat
sided eggs.

80. Laboratory...
4/3/2023 81
2. Finding eggs in the faeces
– Eggs can also be found stool, but less frequently
– Less then 10% found in stools, i.e. not a useful
examination;
– occasionally eggs can be found in the urine or
vaginal smears

81. Laboratory...
3. Finding of female worms from perianal skin or
faeces
Adult worms are also diagnostic, when found in the
perianal area, or during ano-rectal or vaginal
examinations
4/3/2023 82

82. Treatment
 Pyrental Pamoate or Mebendazole
Prevention and Control
1.Treating all members of a family in which infection
has occurred
2. Wearing tight-fitting cotton pants to infected children
4/3/2023 83

83. 3. Washing of the anal skin each morning
4.Washing of clothing worn at night
5. washing hands after using toilet and before
eating , avoidance of putting fingers in the
mouth & trimming finger
4/3/2023 84

84. 4.2.4.Strongyloides stercoralis
Common names: name: Dwarf thread worm
Epidemiology
Found worldwide
An estimated 50 to 100 million persons are infected
worldwide
Favors warmer tropical and subtropical climate
Rarely found in temperate zones
4/3/2023 85

85. 4/3/2023 86
In Ethiopia
 not highly prevalent in most areas and is found
in the same geographical areas with
hookworm
 rates up to 44% reported from 41 of the 50
communities in central and northern Ethiopia
 The infection is rare or absent in many arid
lowland areas, including the Ogaden and
pastoral areas in the Awash Valley

86. 4/3/2023 87
– Worms can be free-living in
the soil or live in a host.
– The definitive host is
humans, but may also affect
other primates and dogs

87. 4/3/2023 88
• S. stercoralis show the following
characteristics
Parasitic males are absent (Only Strongyloides
females are parasitic).
1. Parasitic females are present in the
submocusa of small intestine which produce
egg parthenogenically
2. Can develop in to free living generation in
the soil out side the human host
3. Has internal out infection

88. 4/3/2023 89
Habitat
 Has both free living and parasitic generations
 Parasitic Adult females: buried in the mucosal
epithelium of the small intestine of man
 Egg : laid in the sub mucosa of small intestine (first-
stage larvae hatch from the eggs and are shed in stool)
 Rhabditiform larvae: Passed in the faeces and
external environments
 Filariform larvae: soil and water the infective stage
 Free living male and female : on external
environment

89. 4/3/2023 90
Morphology
The size and shape of the worm are dependent
on whether it’s parasitic or free-living.
• Free-living females – 1 mm by 60 µm
• Parasitic females – 2.2 mm by 45 µm
• Eggs – 55 µm by 30 µm:as soon as they are laid in
sub mucosa, the rhabditiform larvae

90. 4/3/2023 91
Larvae
Rhabditiform larvae
(non-infective form)
Filariform larvae
(pathogenic form)

91. 4/3/2023 92

92. 4/3/2023 93
Morphology-Larva
• Rhabditiform Larvae
– Size: 200-300m long ;
15m thick
– Motility: very actively
motile in the stool
– Tail: Moderately tapered
– Short buccal cavity and
rhabiditiform esophagus
• Filariforml Larave
– About 600-700m
– Cylinderical esophagus
– Bifid tail end

93. Transmission and Life cycle
• Transmission
1. Commonly by penetration of skin by filariform larva
2. Ingestion of food or water contaminated with
filariform larva( oral rout)
3. Rarely: Transmamary & Organ transplantation
4. Autoinfection with rhabidit form larva
4/3/2023 94

94. Life Cycle
 Complex , Two types of cycles exist:
1.Free-living (indirect) cycle
Rhabditiform larvae(stool) molt 4x free-
living adult males and females produce eggs
rhabditiform larvae develop to free living
adult males or females
Filariform larvae(this initiate parasitic life cycle)
4/3/2023 95

95. 4/3/2023 96
2.Parasitic (direct) cycle
Rhabditiform larvae(stool) molt 2x develop to
filarifrom penetrate skin lung Alveolar
space bronchial tree pharynx
swallowed &develop to adult female in small
intestine(molt 2x) produce egg by
parthenogenesis which yield rhabditiform larvae
Life Cycle

96. 4/3/2023 97
 Autoinfection, the rhabditiform larvae become
infective filariform larvae in the host tissue
,penetrate
 intestinal mucosa (internal
autoinfection) or
perianal area (external autoinfection)
The first-stage larvae can transform into infectious larvae
during the intestinal passage or
penetrate into the body through the large intestine or
perianal skin.

97. 4/3/2023 98

98. 4/3/2023 99
Clinical feature
• It is usually asymptomatic, in symptomatic cases
• People with weaker immune systems
such as elderly people and children
are more susceptible
1.Cutaneous phase
 Skin lesionsare observed when the larvae of Strongyloides
species penetratethe skin, in particular in sensitized persons.
 large number of larva produce itching and erythema at the
site of infection within 24 hours of invasion

99. 4/3/2023 100
2.Pulmonary phase:
 The migrating larvae provoke hemorrhages and
inflammatory reactions
 in the lung producing bronchopneumonia and full
blown pneumonitis
3. Intestinal phase :
 Invasion by adult worms may produce abdominal pain and
mucus diarrhea , nausea vomiting and anemia

100. 4/3/2023 101
Auto- and hyper-infection syndromes
A Strongyloides infection can persist in a latent state for
many years due to continuous autoinfection
If immune defense is compromised, by AIDS or
immunosuppressive therapy, parasite reproduction
can be stimulated, resulting in massive systemic infections
(hyperinfections)
characterized by massive larval invasion of the lung or any
other organ including CNS, which is fatal
Systemic infection

101. 4/3/2023 102
Laboratory Diagnosis
1.Finding the larvae in faeces or in duodenal
aspirates using direct or concentration method
by microscopy
 Better results can be expected if duodenal fluid is
examined
 In hyper-infection syndrome the larva may be
found in sputum, urine and in other specimens
 Examination of serial samples may be necessary
because direct stool examination is relatively
insensitive

102. 4/3/2023 103
• The stool can be examined in wet mounts:
– Directly
– After concentration (formalin-ethyl acetate)
– After recovery of the larvae by the baermann method
and/or larval culture
– After culture by the harada-mori filter paper technique
– After culture in agar plates

103. 4/3/2023 104
2. Serological tests
• Antibody Detection
• Indicated when the infection is suspected and the organism
cannot be demonstrated by:
• duodenal aspiration, string tests, or
• by repeated examinations of stool
• Use antigens derived from filariform larvae for the highest
sensitivity and specificity
• (EIA) s currently recommended because of its greater
sensitivity (90%).
• By using recombinant proteins as antigens in the
ELISA

104. 4/3/2023 105
Treatment
Ivermectin or thiabendozole
Prevention and Control
1. Sanitary disposal of faeces in latrine
2. avoid use of night soil as a fertilizer
3. Wearing protective footwear.
4. Travelers returning from tropical countries should be
examined for Strongyloides infections before
any immunosuppressive measures are initiated.
5. Treatment of infected individuals and Health
education

105. 4/3/2023 106
Wear Shoes.
…Don’t eat dirt.

106. • Strongyloides fuelleborni is mainly a parasite of African
monkeys, but is also found in humans.
Geographical Distribution
 Widely distributed in Zimbabwe, Zambia, Papua New
Guinea, co-exists with S.stercoralis in Ethiopia
 It is a common parasite of old world monkeys , apes
&dog
4/3/2023 107
Strongyloides fuelleborni

107. 4/3/2023 108
Transmission and life cycle
Transmission
 Skin penetration by filariform larvae
 Transmammary
Habitat:-Has both free living and parasitic life
Life cycle
 similar to S.stercoralis except it shed eggs in the feaces

108. 4/3/2023 109
Pathology and treatment: similar to S.stercoralis
Laboratory diagnosis
Finding eggs in fresh stool specimens
Egg:-Resembles eggs of hookworms but are
shorter and smaller
-Colorless, Oval and 50 by 35μm in size
-Contain partially developed larvae
– N.B. If there is a delay in examining the feaces , the
larva will hatch

109. 4/3/2023 110
Prevention and Control
 The same as described for S. stercoralis

110. 4.2.5. Hook Worms
 Are hematophagous nematodes
 Two major species
Ancylomstoma duodenale
Necator americanus
 are common parasites of the human small intestine,
causing enteritis and anemia.
 Larvae of various hookworm species from dogs and other
carnivores can penetrate into human skin, causing the
clinical picture of “cutaneous larva migrans”
 Less important :
A. ceylanicum, A. braziliense ,A. caninum ,
A.tubaeforme, A. buckleyi
4/3/2023 111

111. Epidemiology
widely distributed throughout the tropics and subtropics
more than 1 billion people are infected world wide
cause daily blood loss of 7 million liters
Most commonly infected are children, agricultural workers
and miners
Ancylostoma is found in Europe around the Mediterranean,
on the West coast of South America and in parts of China
and India
Necator is found over much of the western hemisphere,
Africa and South East Asia
4/3/2023 112

112. • In Ethiopia : Necator americanus are more
common than Ancylostoma duodenale
highest infection rates: Ilubabor, Kefa
,Welega
A.duodonale is associated with areas
of poor soil coverage and high rate of
drainage
N.americanus is found in red soil
areas on flat plain
4/3/2023 113

113. Altitude and moisture is the major factor affecting their
distribution
Hook worm infection is absent in low ,hot dry areas of
Ethiopia and above 2500m altitude.
4/3/2023 114

114. 4/3/2023 115
Habitat
– Adult: Jejunum and less often in the duodenum of man
– Eggs: In the faeces; not infective to man
– Rhabditiform and filariform larvae: free in soil and
water

115. 4/3/2023 116
Morphology : Adult
A.duodenale N.americanus
pathogen city more pathogenic less pathogenic
Size longer and thicker short and thinner
male 8mm 7-9mm
female 10-13mm 9-11mm
Buccal capsule large and oval small and round
Jaw like teeth cutting plates
Buccal cavity short,10-15 m long ,15-16 m in
in length length
lumen is large lumen is short

116. 4/3/2023 117
A.duodenale N.americanus
Shape of head slightly conical rounded
Esophagus-
Intestinal junction no gap gap

117. 4/3/2023 118
• Head is slightly bend
(hook) and
• The mouth carries
characteristic teeth
(Ancylostoma) or plates
(Necator) for
attachment to intestinal
mucosa
• The posterior end of the
male worm is
elaborated into a
copulatory bursa
• The worm's mean life span
Is 1 - 3 years,

118. 4/3/2023 119
Teeth in their buccal cavity enable their attachment to
intestinal mucosa - from where they suck their host's blood
The worm's mean life span Is 1 - 3 years.

119. 4/3/2023 120
Egg:
 2x egg are produced by A. duodenale (20,000egg/day)
than N. americanus
Size : 65-40m
Shape: oval
Shell: very thin and appears as black line
Colour: the cells inside are pale gray
Content: contains an ovum which appears
segmented usually 4-8 blastomeres

120. 4/3/2023 121

121. 4/3/2023 122
Rhabiditiform Larvae Filariform Larvae
1.Size 250-500m 600- 700 m
2.Bucal cavity long short
3.Oesophages 1/3 body length 1/4 body length
4.Tail Pointed end Sharply pointed end

122. 4/3/2023 123

123. 4/3/2023 124
Hookworm rhabditiform larva Hookworm filariform larva

124. Transmission and life cycle
Transmission
 Penetration of the skin by filariform larvae
 Ingestion of the filariform larvae present in the soil or
transmammary
 for A. duodenale, but N. americanus requires transplumonary
migration
 Following oral infection, immediate development in
the intestine is probably possible (i.e., without
migration through various organs).
 Transplacental : rare
4/3/2023 125

125. 4/3/2023 126
Life cycle
• Eggs are passed in the stool , and under favorable
conditions (moisture, warmth, shade),
• rhabditiform larva larvae hatch in 1 to 2 days in the
feces and/or the soil
• After 5 to 10 days (and two molts) they become
become filariform (third-stage) larvae that are infective
• larvae can survive 3 to 4 weeks in favorable
environmental conditions(in moist soil or water
).

126. 4/3/2023 127
• On contact with the human host, the larvae
penetrate the skin and are carried through the veins
to the heart and then to the lungs
• They penetrate into the pulmonary alveoli, ascend
the bronchial tree to the pharynx, and swallowed
• The larvae reach the small intestine, where they
reside and mature into adults
– they attach to the intestinal wall with resultant blood
loss by the host

127. 4/3/2023 128

128. Clinical features
• Hookworms are bloodsuckers.
• The buccal capsule damages the mucosa and induces
inflammatory reactions
• Clinical feutures arise from a combination of
– Intestinal inflammation
– progressive iron/protein-deficiency anemia
• Most individuals with hookworm infection are
asymptomatic (90%)
• high loads of the parasite (20 - 100 worms) coupled with
poor nutrition (inadequate intake of protein and iron)
eventually lead to anemia
4/3/2023 129

129. Clinical...
• Skin penetration and associated secondary bacterial
infection can result in “ground itch”
• Pulmonary phase is usually asymptomatic
• Intestinal phase: adult worms attach to the mucosa
and feed on blood.
– Worms continuously move to new places
exacerbating bleeding
4/3/2023 130

130. 4/3/2023 131

131. 4/3/2023 132

132. 4/3/2023 133
• The main concern with hook
worm disease is blood loss
• 0.03 ml (N.a.) to 0.26 ml (A.d)
per worm,
• up to 200 ml per day in heavy
infections
• Chronic heavy infection results in
anemia and iron deficiency
• Together with malnutrition
infection can severely stunt
growth and development in
children
• Anemia leads to weakness and
fatigue in adults

133. 4/3/2023 134
Table 2. Clinical features of hookworm disease
Site Symptoms Pathogenesis
Dermal
Local erythema, macules,
papules (ground itch)
Cutaneous invasion and
subcutaneous migration
of larva
Pulmonay
Bronchitis, pneumonitis and,
sometimes, eosinophilia
Migration of larvae
through lung, bronchi,
and trachea
Gastro-
intestinal
Anorexia, epigastric pain and
gastro-intestinal hemorrhage
Attachment of adult
worms and injury to
upper intestinal mucosa
Hematolg
ic
Iron deficiency, anemia,
hypoproteinemia, edema, Intestinal blood loss
Symptoms of hookworm infection depending on the site at which the worm is present and the
burden of worms

134. Laboratory Diagnosis
4/3/2023 135
1.Finding eggs in faeces
 A.duodenale and N.americanus eggs morphologically
indistinguishable
• Microscopic identification of eggs in the stool is the most
common method
• The recommended procedure:
1.Collect a stool specimen.
2.Fix the specimen in 10% formalin.
3.Concentrate using the formalin–ethyl acetate
sedimentation technique
4.Examine a wet mount of the sediment.

135. The diagnostic stage is the egg in the feces. Eggs of
both species look the same
4/3/2023 136

136. 4/3/2023 137
Freshly passed faeces should be examined
If more than 12 hours old ,a larva may be seen inside
the egg
If more than 24 hours old ,the larva hatch
 hookworm : deep buccal cavity
 S. stercoralis : shorter buccal cavity

137. 4/3/2023 138

138. 4/3/2023 139
Eggs that can be mistaken with hookworm egg
 Trichostrongylus species
Ternidens deminutus
 S. fuelleborni
 oesophagostum species

139. 4/3/2023 140
2.PCR
For diagnosis of A. duodenale infection
Epidemiological studies and monitoring of
success of control programs
3. Serological tests (IgG and IgE)

140. 4/3/2023 141
Treatment
 Pyrantel pamoate, Mebendazole or Thiabendazole
 if anemic : high protein diet supplemented with
ferrous sulphate, folic acid and vitamin B12
Prevention and control
As described for Strongyloides stercoralis

141. Larva migrans
1. CUTANEOUS LARVA MIGRANS
2. VISCERAL LARVA MIGRANS
3. OCULAR LARVA MIGRANS
1. CUTANEOUS LARVA MIGRANS
 Larvae of various hookworm species from dogs and other carnivores
can penetrate into human skin, causing the clinical picture of
“cutaneous larva migrans
 Since human are not natural host of the parasite larvae may undergo
larval arrest thus unable to complete its life cycle.
 Caused by larvae of cat hook worm (Ancylostoma braziliense) & dog
hook worm (Ancylostoma caninum) in man
 Commonly seen in children in the tropics and sub tropics
4/3/2023 142

142. CUTANEOUS LARVA...
 The filariform form larva are able to infect by skin as
well as by mouth
 When the larvae invade the skin , the produce itching
papule which become creeping or extending red linear
skin lesions in the skin within 2 or 3 days
 Movement of larva may extend the lesion several
millimeters/day
4/3/2023 143

143. 4/3/2023 144
Image 037_02. Cutaneous Larva Migrans. Cutaneous larva migrans lesions of the foot of a 10-year-old girl. In
the United States this dog and cat hookworm infection is most commonly seen in the southeastern states.
These raised, serpiginous, pruritic, migrating eruptions may extend rapidly.
Red Book Online Visual Library, 2006. Image 037_02. Available at:
http://aapredbook.aappublications.org/visual. Accessed December 7, 2007

144. 4/3/2023 145
Image 037_01. Cutaneous Larva Migrans. Cutaneous larva migrans lesions on lower leg (caused by hookworm
larvae of Ancylostoma braziliense and Ancylostoma caninum).
Red Book Online Visual Library, 2006. Image 037_01. Available at:
http://aapredbook.aappublications.org/visual. Accessed December 7, 2007

145. 4/3/2023 146
Image 037_05. Cutaneous Larva Migrans. Cutaneous larva migrans infection of the foot in an adolescent male
Red Book Online Visual Library, 2006. Image 037_05. Available at:
http://aapredbook.aappublications.org/visual. Accessed December 7, 2007

146. 4/3/2023 147
Image 037_04. Cutaneous Larva Migrans. Adult who noted a migrating skin lesion on left thigh for 2 weeks.
Red Book Online Visual Library, 2006. Image 037_04. Available at:
http://aapredbook.aappublications.org/visual. Accessed December 7, 2007

147. 4/3/2023 148
Laboratory diagnosis
Can be made by inspection of lesions along with the
characteristics history of exposure
Treatment
Oral or topical application of thiabendazole or DEC
Prevention and control
Deworming of cats and dogs
Removed of vagrant cats and dogs from areas of
human habitation

148. 4/3/2023 149

149. 2. VISCERAL LARVA MIGRANS
Migration of larval nematodes of the
migration of larvae through the tissues and
consequent clinical symptoms and pathogenesis
associated with the larval present
dog ascarid (Toxocara canis ) ,
the cat ascarid (Toxocara catis )
larvae don't complete their normal cycle of
development as their movement is arrested at
some level of the human body
4/3/2023 150

150. Toxocara canis
The dog ascarid
Larva causes visceral larva migrans(VLM)
(toxocariasis or toxocaral disease) & ocular larva
Migrans(OLM) (granulomatous opthalmitis) in
man
Causes a common infection in dogs through out the
world
Infection rates in dogs varies from 2-90%
4/3/2023 151

151. • Adult are in small intestine of canid: dogs , fox
– high egg production, larvae in egg capsules
for long periods of time
• Human ,especially children, & rodents can be
paratenic hosts; they harbor migrating larvae
• Human become infected by ingesting infective egg
 children playing with puppies or in parks or in other
areas contaminated with dog faeces , are particularly at
risk
4/3/2023 152
Toxocara canis

152. Life cycle
 In dog is similar to that of Ascaris lumbicoides in man
 Unembroynated egg passed in faeces
 it requires further maturation outside the host
 The infective egg ingested by dog, rodents and human and the
larvae hatch in small intestine
 In puppies younger than 5 weeks , the larvae complete
migratory and developmental cycle similar to that of Ascaris
lumbicoides in human host and grow to adult in the intestine
4/3/2023 153

153. Life cycle
 In adult puppies , adult dogs or human host ,the larvae
unable to complete their development
 In these hosts , the larvae may wander in the tissue for
some time and encyst as second stage larvae
 In pregnant bitches , dormant L2 larvae excyst/
reactivated by hormonal change and cross the placenta to
grow to adult worm in the fetuses
 In human the L2 which hatch in the gut , migrate through
tissues causing VLM or if trapped in the eye ,OLM
4/3/2023 154

154. VISCERAL LARVA MIGRANS(VLM)
In the course of migration ,they cause
eosinophilic inflammation followed granuloma
formation around dead larvae
Characterized by persistent eosinophilia in the
peripheral blood ,fever & often occurring along
with the involvement of the lung or liver or both
4/3/2023 155

155. Ocular Larva Migrans (OLM)
is potentially more serious as the retina may
damaged and in extreme cases may result in
loss of visions or sever ocular inflammation
4/3/2023 156

156. Toxocara catis
 The cat ascarid
 Cosmopolitan distribution
 It’s life cycle similar to Toxocara canis except there is no
transplacental transmission
 It’s egg develop to L2 in earthworm, cockroaches , mice &
dogs
 Cats become infected by ingesting mice harboring larvae in
their tissues
 Larval T. cati infection in human rarely cause VLM
4/3/2023 157

157. Laboratory diagnosis of VLM
Finding of larvae in biopsies, especially liver, but
larvae are only rarely found
Serological tests using L2 of Toxocara as an antigen
Treatment
Thiabendazole & DEC
Corticosteroids: sever pulmonary , myocardial& eye
inflammation
4/3/2023 158

158. Prevention and control
Antihelminthic treatment of dogs
Excluding dogs from children playing areas
Improve sanitation ,education , Safe water supply
& Chemotherapy to interrupt transmission
infective egg to water, food or human hands
4/3/2023 159

159. 4/3/2023 160