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
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
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
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
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
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
27.
28. Morphology of Eggs
Egg
• Oval, clear and colorless
• 50 to 60 µm in length, thick shell
• Flattened on one side
• Contains a larva
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
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