1. B.E Pruitt & Jane J. Stein
Trichuris trichura
Enterobius vermicularis
Dr Kamran Afzal
Classified Microbiologist

2. Taxonomic Classification of Helminths
Sub
kingdom
Phylum Class Genus – examples
Metazoa Nematodes
Round worms; appear round
in cross section, they have
body cavities, a straight
alimentary canal and an anus
Platyhelminthes
Flat worms; dorsoventrally
flattened, no body cavity and,
if present, the alimentary
canal is blind ending
Cestodes
Adult tapeworms are found in
the intestine of their host
They have a head (scolex) with
sucking organs, a segmented
body but no alimentary canal
Each body segment is
hermaphrodite
Taenia (tapeworm)
Trematodes
Non-segmented, usually leaf-
shaped, with two suckers but
no distinct head
They have an alimentary canal
and are usually hermaphrodite
and leaf shaped
Schistosomes are the
exception. They are thread-like,
and have separate sexes
Fasciolopsis (liver fluke)
Schistosoma (not leaf
shaped!)

3. Taxonomic Classification of Helminths
Sub
kingdom
Phylum Class Genus – examples
Metazoa Nematodes
Round worms; appear round
in cross section, they have
body cavities, a straight
alimentary canal and an anus
Ascaris (roundworm)
Trichuris (whipworm)
Ancylostoma
(hookworm)
Necator (hookworm)
Enterobius (pinworm or
threadworm)
Strongyloides
Platyhelminthes
Flat worms; dorsoventrally
flattened, no body cavity and,
if present, the alimentary
canal is blind ending
Cestodes
Adult tapeworms are found in
the intestine of their host
They have a head (scolex) with
sucking organs, a segmented
body but no alimentary canal
Each body segment is
hermaphrodite
Taenia (tapeworm)
Trematodes
Non-segmented, usually leaf-
shaped, with two suckers but
no distinct head
They have an alimentary canal
and are usually hermaphrodite
and leaf shaped
Schistosomes are the
exception. They are thread-like,
and have separate sexes
Fasciolopsis (liver fluke)
Schistosoma (not leaf
shaped!)

4. Characteristics of Nematodes
 Cylindrical and unsegmented
 Dioecious (male and female)
 Complete digestive tract (mouth / esophagus / intestine / anus)
 Adults: sexually reproductive life cycle stage
 Larvae: developmental or asexually reproductive life cycle stage
 Eggs: protective stage of zygote &/or embryo
 Oviparous: production of eggs, discharged from uterus of female
 Viviparous: production of embryos/L1 larvae, no rigid
encapsulation of embryo

5. Intestinal Parasites : Mode of infection
Ingestion of cysts,
oocysts or ova
Entry of larvae or
oncospheres
Site of adult stage
or disease
Cryptosporidium
Giardia
Amoebiasis
Intestine
Toxoplasmosis
Visceral larva migrans
Trichinella Ingested Disseminated
Ascaris
Trichuris
Enterobius
Hookworm
Strongyloides
through skin
Intestine

6. Intestinal Parasites : Symptoms
Symptoms Parasite
Abdominal pain and distension Giardia
Cryptosporidium
Amoebiasis
Ascaris, hookworm, taenia
Diarrhoea +/- malabsorption Giardia
Cryptosporidium
Strongyloides
Diarrhoea with blood loss Amoebiasis
Trichuris
Hookworm
Tenesmus, prolapsed rectum Trichuris

7. Case History - 1
 8-yr-old schoolgirl visiting Pakistan from Malaysia
 1 week history of epigastric pain, flatulence, anorexia, bloody
diarrhea
 No eosinophilia noted
 Clinical diagnosis of amoebic dysentery made

8.  However, microscopy of stool prep…

9. B.E Pruitt & Jane J. Stein
Trichuris trichura
The ‘Whip-worm’

10. 50 mm long with a slender anterior and a thicker posterior end
The male is smaller and has a coiled posterior end
Morphology - of Adult worms

11. Morphology - of Eggs
 Eggs in stool
 Size: 50-54 µm by 22-23 µm,
 Shape is a typical barrel
 Color is yellow-brown
• Unstained two polar plugs
 Shell quite thick
 Contains unembryonated egg

12. Life cycle

13. Life cycle

14.  Humans sole host
 Transmission
• Fecal-oral via embryonated ova
 Frequently coexists with ascaris
 Reservoir
• Mainly human, others possible but host specificity not well
documented
 Pathogenic potential
• Low to moderate, dependent on worm numbers and location
in LI
Pathogenesis

15.  Entirely intraluminal life cycle—eggs are ingested
 Eggs hatch in intestines, larvae attach, and develop into adults
 Female lays 3,000-5,000 eggs daily
 Worms can pierce capillaries, cause localized hemorrhage, and
allow bacteria to leave intestine

16. Clinical Features
 Frequently asymptomatic
 Clinical signs/symptoms - Adult worm (Pathogenic stage)
• Dependent on no. of worms; None to digestive disturbances,
bloody (frank)/ mucoid diarrhea, abdominal pain and
distention, rectal prolapse, anemia and weakness
 Severe infections
• Tenesmus and rectal prolapse in children
• Can be fatal in children
• Rarely, elephantiasis in adults

17. •Trichuris trichiura in the large intestine
•Many worms are present, each with its anterior end embedded in the
intestinal mucosa, resulting in the erythema

18. Lab Diagnosis
 Stool
• Direct examination (Iodine stain)
• Eggs
• Rarely adult worms
 Blood
• Eosinophilia
 Histopathology of the intestinal mucosa
 PCR

19. Imaging
 X-Rays Abdomen
• Plain
• With contrast / dye
 CT Scan

20. Treatment and Prevention
 Albendazole 400 mg once
 Mebendazole
100 mg BD for 3 days
(600 mg, repeated after 2 weeks)
 Pay attention to personal hygiene and eating habits

21. Case History - 2
 11-year-old female
 Doing poorly in school
 Not sleeping well
 Anorectic
 Complains of itching in rectal region throughout the day

22.  A Scotch-tape test reveals…

23. B.E Pruitt & Jane J. Stein
Enterobius vermicularis
The ‘Pin-worm’

24. Helminthic Diseases of the Digestive System

25. Epidemiology
 Enterobiasis most common worm disease of children in
temperate zones
 Pre-school and elementary school children affected most often
 Consmopolitan, 30%~50% of the children population is infested
 Most common where people live under crowded conditions
(orphanages / large families / kindergartens / primary school)

26. Morphology of Adult
 Adult
• Female: White 8~13 mm in size
Fusiform body with a long, thin, sharply tapering tail
Alae (cuticular extension of head)
Prominent bulb – Rhabditiform esophagus
The greater part of the body is occupied by the
uterus filled with eggs
• Male: Like female, but about 1/3 to 1/2 size of female
The tail is curved, it is rarely seen

28. Morphology of Eggs
 Egg
• Oval, clear and colorless
• 50 to 60 µm in length, thick shell
• Flattened on one side
• Contains a larva

29. Enterobius vermicularis (Pinworm)

30. Transmission
 Definitive host
• Human
 Transmitted by
• Ingesting Enterobius eggs

31. Pathogenesis
 Infective stage
• Infective eggs
 Eggs are picked up from surroundings and swallowed
• Being sticky, adhere to door handles (especially toilet doors),
bedclothes and mug handles etc
 After hatching in the small intestine, they develop into adults
 The location of adult
• Cecum and colon
 Anal itching occurs when mature females emerge from
intestine to release eggs
• Life span of female adult is 1-2 months
 Right after mating, the male dies
• Therefore, the male worms are rarely seen
 Self-inoculation is common

32. Life Cycle

33. Life Cycle

34. Clinical Features
 Mostly asymptomatic
 Nocturnal anal pruritis is cardinal feature due to migration
and laying of eggs
 Perianal pruritus may lead to excoriations and bacterial
superinfection
 Occasionally, invasion of the female genital tract with
vulvovaginitis and pelvic or peritoneal granulomas can occur
 Other symptoms : anorexia, irritability, and abdominal pain
 May have insomnia, possible emotional symptoms

35. Types of infection
 Infection from environment
 Auto-infection
• Female crawls out of anus and release eggs on the perianal
region
• Patient feels anal pruritus
• Scratching leads to contamination of hands and nails
• Re-infection is by hand-mouth transmission
 Retro-infection
• Some eggs hatch on the perianal skin and become larvae
• They will crawl back into the anus and mature into adults

36. Laboratory Diagnosis
 Direct fecal smear
• Microscopic identification of eggs collected from the perianal
area is the method of choice by
• Scotch tape technique
• Cellophane tape impression
• This must be done in the morning, before
defecation and washing
 Alternatively, anal swabs can also be used
 Brine-floatation method
 Detection of adult on anal skin at night,
when the child is sleeping
 Larval cultivation

37. Treatment
 Since the life span of the pinworm is less than two months,
the major problem is re-infection
 Repeat the treatment after 2 weeks
 Repeated re-treatment may be necessary for a radical cure
 Albendazole is the drug of choice
 Mebendazole and Pyrantel pamoate are the alternative drugs

38.  Treat and re-treat the patients and carriers
 Laundering of bedding
 Individual health
• Observation and correction of personal hygienic and
eating habits
 Public health
 Health education
Prevention