Chapter 2_Nemathyheliminthes_Intestinal Nematodes.pdf

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1. Chapter 2
Nemathyhelminthes/Round worms/
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2. Outline
Introduction to Nemathelminths (Nematoda)
General characteristics
 Classification
1.Intestinal nematodes
2.Tissue nematodes
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3. Introduction to Nemathelminths (Nematoda)
•The Greek name ‘nema’ means ‘thread’ & ‘helmins’ -
means ’worms’. …. Thread-like worm
•Helminthes are macroscopic, multicellular worms possessing
well differentiated tissues and complex organs.
–A particular function such as reproduction, digestion
or excretion is performed by a group of special cells.
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4. General Characters of Nematodes
•Elongated, cylindrical, unsegmented worm with bilaterally
symmetrical body tapering at both ends
•Variable in size, measure <1 cm to about 100cm
•Sex separate (diecious), male is smaller than female.
•Females are either viviparous, oviparous or ovo-viviparous
•Digestive system complete
➢ Possess mouth, oesophagus and anus
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5. Morphology of Nematodes
•Developmental stages include
•Egg ->Larvae (rhabditiform, filariform & microfilaria)->
Adults
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6. Classification of Nematodes
•Based on the Location in the human body
1.Intestinal nematodes
•Small Intestine: Ascaris, Hookworm, Strongloid
•Large Intestine: Whip worm, Pinworm
2.Tissue nematodes
•Lymphatics & subcutaneous tissues: Filaria
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INTESTINAL ROUND WORMS

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Introduction To Intestinal Nematodes
•Live in gastro-intestinal tract
•In humans, often spread by poor hygiene related to
feces
•Most species are geo-helminths (soil transmitted)
•Humans are the only or major host of intestinal
nematode

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Transmission of Intestinal Nematodes
•Ingestion
•Skin penetration
•Inhalation
•Auto-infection
•Retro infections

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Larvae pass
through lungs
Larvae penetrate
through intact skin
strongyloides
hookworm
Eggs ingested
Trichiuris (whipworm)
Enterobius (pinworm)
Larvae enter
bloodstream
Ascaris
Adult worms in the
the intestine
Eggs
Larvae hatch
from eggs
Life Cycle of Intestinal nematodes

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Key to the diagnosis of Intestinal Nematodes
Intestinal
Nematodes
Larvae in Stool
S. stercoralis
Eggs in stool
Eggs on
Perianal Skin
Colored
(Bile Stained)
A. lumbricoides
T. trichiura
Colorless
(Non Bile Stained)
E. vermicularis
Colorless
(Non Bile Stained)
A. duodenale
N. americanus
E. vermicularis

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Nematodes

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Reporting results
⚫Lynne S. Garcia et al (2018) Laboratory Diagnosis of Parasites from the
Gastrointestinal Tract. Clinical Microbiology Reviews January 2018 Volume 31
Issue 1 e00025-17

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Treatment
•Rehydration – oral vs. Iv
•Antiemetics
•Surgical removal
•Adequate nutrition

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Preventing Worm Infection

16. 1.Ascaris lumbricoides (Large intestinal Round worm)
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17. Ascaris lumbricoides
•The name is derived from ‘Askaris’ means ‘intestinal worm’ & ‘lumbricoides’ is Latin
means ‘earthworm’ because it resembles earthworm.
•Disease: it causes Ascariasis
•Morphology: EGG (fertilized or unfertilized), LARVAE (L1- L2 in tissues) &
ADULT
•Epidemiology: transmitted by ingestion of eggs (in contaminated food water or
finger). Humans are the only hosts. Infection occurs in all age groups, but most
common in preschool & young children
•Life cycle: ingest embryonated eggs → release larvae in gut → larvae migrate
to the lungs → enter the alveoli → pass up the trachea → swallowed →
become M & F adults in the SI → lay eggs → passed in feces → become
infective in soil.
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18. Ascaris lumbricoides
•Pathogenesis:
–Larvae in lung can cause minute hemorrhage & Eosinophilic
pneumonia (Loeffler’s syndrome due to allergic reaction).
–Heavy adult infection cause complication like Intestinal obstruction
and perforation, biliary tract blockages) or malnutrition (Vit. A,
Protein), allergic manifestations like & urticaria due to toxic fluid
(ascaron or ascarase) released by the adult worm.
•Clinical Features:
–Asthma or pneumonia like symptoms like cough, bloody sputum,
shortness of breath & wheezing& eosinophilia in heavy larval burden.
–Light adult infection is asymptomatic but abdominal pain, vomiting,
fever, and distention, obstruction, malnutrition, & perforation in
heavy adult infection.
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19. A. lumbricoides
•Lab. Dx: Adult & eggs in feces, larva in sputum and high
eosinophil count in blood.
•Rx: Mebendazole or pyrantel pamoate.
•Prevention: proper disposal of human waste, mass treatments
(if prevalence >50%) & wash fruits and vegetables
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2. A. duodenale & N. americanus (Hookworms)

21. Ancylostoma duodenale & Necator americanus
•The word Ancylostoma duodenale (Greek ankylos - hooked; stoma -mouth)
… ‘Old World’ hookworm
•The word Necator americanus literally means the ‘American murderer’ (Latin
necator - murderer). …. New World’ hookworm
•Disease: Hookworm infection
•Morphology: Egg ….. Larva (Rhabditiform, filariform) … Adult
•Epidemiology: Filariform larvae penetrate skin of feet or
hands. Humans are the only hosts. Both species are found in
Ethiopia, but N. americanus is more common
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22. Ancylostoma duodenale & Necator americanus
•Life cycle: Larvae penetrate skin →enter the blood →migrate to lungs &
enter alveoli →pass up the trachea → swallowed →become adults in SI &
attach to walls via teeth (Ancylostoma) or cutting plates (Necator) → produce
eggs → passed in feces → hatch & develop to rhabditiform larvae → then
filariform larvae.
•Pathogenesis: disease can be caused by the larvae or adult.
–Repeated exposure to larva causes hypersensitivity rxn known as
“ground itch or dew itch’’ at entry site;
–Attachment of adult on jejunal mucosa leads to traumatic damage
of villi and bleeding at the site of attachment.
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23. Ancylostoma duodenale & Necator americanus
•Clinical Features:
–Ground itch (dermatitis): a pruritic erythematous & papular rash on
hands & feet, creeping eruption along the path of migration (larva
migrans) & lesions in the lungs.
–Adult causes epigastric pain, diarrhea & vomiting at early phase of
infection and anaemia due to chronic blood loss from GI tract.
•Lab. Dx: non-bile stained segmented eggs in feces. Eosinophilia occurs.
•Rx: Mebendazole or pyrantel pamoate to kill the parasite & Oral iron
replacement; ferrous sulphate
•Prevention: Use of footwear, proper disposal of human waste and Personal
hygiene
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3. Strongyloidiasis stercoralis(thread worm)

25. Strongyloidiasis stercoralis
•These were named S. stercoralis (strongylus - round; eidos - resembling;
stercoralis - fecal).
•Disease: it causes Strongyloidiasis.
•Life cycle: penetrate skin →enter the blood →migrate to lungs & into
alveoli →pass up the trachea & swallowed →become adults and enter
the mucosa where females produce eggs →hatch into rhabditiform larvae
→passed in feces →form infectious filariform larvae in the soil →these
larvae can either penetrate the skin or form adults for free-living cycle
–The noninfectious rhabditiform larvae in the intestine occasionally
molt to form infectious filariform larvae that can enter the blood and
migrate to the lung (autoinfection).
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26. Strongyloidiasis stercoralis
•Epidemiology: Filariform larvae in soil penetrate skin. Endemic in the
tropics.
•Pathogenesis: it may have cutaneous, pulmonary, and intestinal
(burrowing lesions) phase. Little effect in immunocompetent persons but
massive superinfection accompanied by secondary bacterial infections in
immunocompromised persons.
•Clinical Features: cutaneous (itching and dermatitis), pulmonary
(hemorrhages & bronchopneumonia - Fever, cough, haemoptysis, dyspnea),
and intestinal (burrowing lesions … epigastric pain with tenderness,
diarrhoea or constipation and weight loss)
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27. Strongyloidiasis stercoralis
•Lab. Dx: Larvae visible in stool. Eosinophilia occurs.
•Treatment: Ivermectin is the drug of choice. Thiabendazole is
an alternative.
•Prevention: Proper disposal of human waste
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4. Enterobius vermicularis (Pin Worm, Seat worm)

29. Enterobius vermicularis
•The name E. vermicularis is a Greek word ‘enteron’ - intestine, ‘bios’ -
life, and ‘vermiculus’ - small worm).
•Disease: It causes pin worm infection (enterobiasis).
•Morphology: egg, larvae in intestine & adult
•Epidemiology: transmitted by ingesting, inhalation of embryonated
eggs and retroinfection. Humans are the only hosts. Occurs worldwide
•Life cycle: ingest eggs →larvae hatch in the intestine →develop into
adults →females migrate to anus & lay eggs at night →embryo within
egg becomes infective within 4-6 hours. Reinfection is common.
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30. E. vermicularis
•Pathogenesis: Perianal pruritus is thought to be an allergic reaction to
the presence of either the adult female or the eggs. Scratching predisposes
to secondary bacterial infection
•Clinical Features: As the worm migrates out at night, it disturbs sleep
causing Insomnia and restlessness Migration of worm and eggs cause
itching that worsens at night.
•Lab. Dx: non-bile stained eggs visible by “Scotch tape” technique (95%)
& stool (5%) microscopically. And adult worms found in feces or
perianal region.
•Treatment: Mebendazole or pyrantel pamoate kill the adult worms in the
colon but not the eggs, so that retreatment in 2 weeks is suggested.
• Prevention: None (or mebendazole)

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5. Trichuris trichiura (Whip Worm)

32. 5. Trichuris trichiura (Whip Worm)
•The name Trichuris means a ‘hair-like tail’ (Greek trichos - hair, oura -
tail).
•This name is not quite correct because it is the anterior end of the worm
that is hair-like and not the tail.
•Disease: it causes Whipworm infection (trichuriasis).
•Life cycle: Humans ingest eggs → develop into adults→ eggs are
passed in feces into soil → embryonate, i.e., become infectious.
•Epidemiology: Transmitted by food or water contaminated with soil
containing eggs. Humans are the only hosts. Occurs worldwide,
especially in the tropics.
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33. T. trichiura
•Pathogenesis: Although adult Trichuris worms burrow their hairlike anterior
ends into the intestinal mucosa, they do not cause significant anemia unlike the
hookworms, they may cause rectal prolapse in children with heavy infection.
Prolapse results from increased peristalsis that occurs in an effort to expel the
worms
•Clinical Features: infection with less than 10 worms is asymptomatic, but
infection with 100-200 worms cause abdominal pain, nausea, vomiting, weight
loss & bloody diarrhea due to increased intestinal secretion & motility.
•Lab. Dx: bile stained eggs with bipolar mucus plugs visible in feces.
•Treatment : Mebendazole.
•Prevention : Proper disposal of human waste
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34. Reading Assignment
•Larva Migrance
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35. 03/05/09 Demiss Nigussie
Thank You
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