Nematodes, Cestodes,
Trematodes
Slackers Facts by Mike Ori
Disclaimer
The information represents my understanding only so errors and omissions are
probably rampant. It has not been vetted or reviewed by faculty. The source is our
class notes.
The document can mostly be used forward and backward. I tried to mark
questionable stuff with (?).
If you want it to look pretty, steal some crayons and go to town.
Finally…
If you’re a gunner, buck up and do your own work.
Describe a nematode
Round spindle shaped worms that range in size
from 1mm to 70cm. They undergo multiple
larval stages. They are dioecious (separate
sexes)
What are the three methods of nematode
infection
1. Ingestion of eggs
2. Ingestion of larva
3. Direct penetration of skin
Describe the relative frequency of nematode
disease in children v adults
Children > adults
What are the intestinal nematoed and what are
their common names
Enterobius vermicularis – pinworm
Trichuris trichura – whipworm
Ascaris lumbricoides – roundworm
Necator americanus – hookworm
Ancylostoma duodenale – hookworm
Strongyloides stercoralis – none
What is the life cycle of Enterobius vermicularis
Ingested eggs hatch in small intestine
Adults live in colon
Eggs deposits in perianal region nightly by
females
How is Enterobius vermicularis diagnosed
Sticky side out Scotch tape wrapped slide is
pressed against perianal region. Tape is
examined under microscope to identify the
presence of eggs
What is the hallmark clinical sx for Enterobius?
Perianal pruritis
What is the lifecycle of Trichuris trichuria?
1. Ingestion of embryonated eggs from
contaminated dirt.
2. Larva hatch in small intestine
3. Adults mature in colon where they burrow
into the surface
4. Eggs are passed in the feces
5. Egg embryonate in the soil over 2-4 weeks
What are the clinical sx of Trichuris
None if worm burden is low. Otherwise
tenesmus with chronic mucoid diarrhea
occurs. Rectal prolapse may occur
Why does rectal prolapse occur with Trichuris?
The adult worms burrow into the epithelium
and weaken it.
Trichuris DX?
O and P for O
What is the lifecycle for Ascaris lumbricoides?
1. Ingestion of embryonated eggs which hatch
in intestines
2. Larva migrate to alveoli
3. L3 larva break through into the alveolar
spaces
4. Larva migrate up trachea and are swallowed
5. Adults mature in small intestines
6. Eggs pass in feces
7. Embryonate in soil for 2-4 weeks
What is the relative size of ascaris?
They can range up to 70cm
Correlate the intensity of disease to Ascaris
chracteristics
Disease intensity is dictated by worm burden.
Higher burden results in greater likelihood of
clinical sx.
Relate eosinophilia to Ascaris infection
Elevated when the worms are migrating to and
especially when they are molting within the
alveoli.
How does Ascaris cause disease in the intestines
Primarily through blockage
Describe Necator americanus lifecycle
1. Eggs hatch in the soil and larvate
2. L3 larva directly penetrate the skin
3. Larva migrate to the lungs and pass through
to the alveolar space
4. They are regurgitated and swallowed
5. Adults mature in the small intestines
6. Eggs pass in the feces
How dow Necator and Ancylostoma vary in their
paths of infection?
Ancylostoma infection can also occur by direct
ingestion of eggs in a manner akin to Ascaris.
Wakana’s disease relates to ancylostoma
infection by ingestion
Describe the clinical disease
Asthma from migration that is less sever than
ascaris because molting does not occur.
Anemia related adult repositioning every few
days in the intestine coupled with anticoagulant
What is the dx for Necator and Acylostoma
Direct microscopic observation of eggs passed in
feces
What is Strongyloides lifecycle
1. L3 larva penetrate skin
2. Larva migrate to lungs and break out of
alveoli
3. Larva migrate up trachea and are swallowed
4. Adults mature in the small intestines
5. Eggs ebryonate and hatch in the host
6. L2 larva pass in feces
7. L3 larva reinfect host
How does Strongyloides infection differ from
that of other intestinal worms?
Strongyloides eggs hatch within the host
resulting in the potential for autoinfection.
Describe Strongyloides disease
1. Pneomonitis
2. Moderate to severe watery, moucousy
diarrhea
3. 10-40% eosinophilia
Strongyloides
What dictates the level of eosinphilia between
Ascaris, Necator, Ancylostoma, and
Strongyloides
Ascaris has the highest reactivity because it
molts L1-L2 and L2-L3 within the tissues. Thus
eosinophilia is highest in ascaris.
Trichenella spiralis lifecycle
1. Ingestion of encysted organisms in
undercooked, non-frozen pork, bear meat,
and rat.
2. Adults mature in the intestines.
3. Larva migrate to the skeletal muscles and
encyst for up to 30 years.
What are the phases of Trichenellosis
Intestinal phase – non-specific gastroenteritis
lasting 2-3 weeks
Parental phase – myalgia, eosinophilia (20-90%)
What is cutaneous larva migrans
Ca and dog hookworm larva penetrate the skin
but cannot enter the circulation. They persist
for about 10 days before dying
What is visceral larval migrans
Toxacara canis and ascaris of dogs cannot break
out of alveoli. Organism disseminates and
encysts primarily in liver and eye.
What is filiariasis?
Infection with tissue nematodes transmitted by
arthropods.
What are the agents of Filariasis?
Wuchereria bancrofti
Brugia malayi
Onchocerca volvulus
Loa Loa
Acanthocheilonema perstans
How do the insect biting pattern and the worm
levels in the blood compare in filariasis?
Worm levels increase in a way such that their
levels coincide with the activity of their insect
vectors. The mechanism is not understood.
Describe the role of antibiotics in the treatment
of filariasis
Many filariasis agents have an endosybiont
bacteria without whom they cannot live.
Therapy directed against the bacteria can be
beneficial
What are the vectors for filariasis
Mosquitoes – most organism
Blood sucking flies – Onchocerca
What are the agents of elephantiasis?
Wucheria bancrofti and Brugia malayi
What is Loa Loa
A filariasis that migrates through the
subcutaneous tissue of the eye.
What is the life cycle of Onchocercosis
1. Blood sucking flies deposit larva in skin
2. Nodules form filled with organisms
3. Black flies ingest larva from nodule
Describe the role of the immune system in
causing Onchocerca disease
The immune system largely ignores adults but
reacts vigorously against the endosymbiotic
bacteria (Wolbachia) contained within. It is
believed the the immune response leads to
disease.
What are tremetodes
Flukes of nature
List the tremetodes
Clonorchis sinensis – Chinese river fluke
Fasciola hepatica – Sheep liver fluke
Pargonimus westermani – Human lung fluke
Schistosomes – blood flukes
Where do adult schistosomes live?
Depends on species.
Mansoni, japonicum, mekongi live in mesenteric
venules
Maematobium in the venus plexus of the
urinary bladder
Where do schistosomes lay their eggs and what
happens to the eggs
Eggs are laid on the venous endothelium. They
pass through the epithelium to be passed in
urine or feces depending on speces
Describe the lifecycle of schistosomes
1. Eggs hatch in fresh water to form miracidia
2. Miracidia pentrate snails and mature to
cercariae
3. Cercariae leave snail and penetrate host.
4. Migrate to lungs and liver and mature to
adults
5. Adults mate and migrate to venous plexus of
mesentery or urinary tract.
6. Eggs are deposited into epithelium where
they burrow through to the epithelium to
pass
What is the origin of granulomatous disease in
schistosomiasis
Eggs float to the liver instead of passing into the
epithelium. In the liver they elicit a strong
immune response that results in granuloma
formation.
What are the time course of the diseases caused
by schistosomiasis
Swimmers itch lasting a 2 days
Katayama fever beginning 2-3 weeks after
exposure
Chronic schistosomiasis beginning 2+ years
What are cestodes
Tapeworms
List the cestodes
Taenia saginata – beef tapeworm
Taenia solium – pork tape worm
Diphyllobothrium latum – fish tape worm
Echinococcus granulosus – dog tape worm
Describe the lifecycle of Taenia solium
1. Ingested eggs hatch in cattle
2. Larva hatch in small intestines
3. Larva penetrate intestinal epithelium
4. Larva migrate to the skeletal muscle to encyst
and develop to cystecerci
5. Encysted meat is improperly cooked and
ingested.
6. Unencyst and develop into adults
7. Proglottids containing eggs break up and eggs
pass in feces
Describe the clinical disease caused by the adult
tapeworm
Usually only one worm present so there is no
clinical disease. PT may notice proglottids in
stool.
What is a proglottid
It is a segment of the worm that contains the
eggs. It developed from a hermaphroditic
segment that contained uterine and testes
elements.
What is cystecercosis
Cystecercosis occurs when a human ingest the
eggs of T. solium and thus becomes the
intermediate host.
What are the clinical sx of cystecercosis
It depends on the worm burden. May form
space occupying lesions in any organ system.
Epilepsy can occur in if cystecerci form in the
brain.
What is the difference between saginata and
solium proglottids?
T. Saginata has 12+ lateral branches of the
uterus vs 5-10 for T. solium
Does T. saginata cause cystecercosis?
No
What is interesting about the lifecycle of
Diphyllobothrium latum?
It is very complicated and involves multiple fresh
water hosts including crustaceans and fish.
What are the clinical sx of D. latum?
Usually none. Can have B12 deficiency.
What is the lifecycle of Echinococcus
granulosus?
Sheen act as intermediate host. Dogs eat sheep
muscle encysted with the organism. Adults
develop.
How do humans enter the Echinococcus
granulosus loop
Humans enter the loop by ingesting material
contaminated with eggs.
What are the sx of Echinococcus granulosus
Large ( 20cm) fluid filled hydatid cysts form in
the liver or viscera.
Describe the disease caused by Echinococcus
granulosus
Usually these are mass forming issues due to the
large size. The Echinococcus is unique in that
it can replicate in the cyst form thus over time
a number of cysts can form.
Describe the consequence of hydatid cyst
rupture.
The fluid is allergenic and can cause anaphylaxis
on rupture. Surgical tx must be done gingerly
to prevent shock.