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 eggs2. 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 – pinwormTrichuris trichura – whipworm

Ascaris lumbricoides – roundwormNecator americanus – hookworm

Ancylostoma duodenale – hookwormStrongyloides stercoralis – none

What is the life cycle of Enterobius vermicularis

Ingested eggs hatch in small intestineAdults 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 intestine3. Adults mature in colon where they burrow

into the surface4. 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 alveoli3. L3 larva break through into the alveolar

spaces4. Larva migrate up trachea and are swallowed

5. Adults mature in small intestines6. 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 larvate2. L3 larva directly penetrate the skin

3. Larva migrate to the lungs and pass through to the alveolar space

4. They are regurgitated and swallowed5. 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 anti-

coagulant

What is the dx for Necator and Acylostoma

Direct microscopic observation of eggs passed in feces

What is Strongyloides lifecycle

1. L3 larva penetrate skin2. Larva migrate to lungs and break out of

alveoli3. Larva migrate up trachea and are swallowed

4. Adults mature in the small intestines5. Eggs ebryonate and hatch in the host

6. L2 larva pass in feces7. 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. Pneomonitis2. Moderate to severe watery, moucousy

diarrhea3. 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 bancroftiBrugia malayi

Onchocerca volvulusLoa 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 organismBlood 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 skin2. Nodules form filled with organisms3. 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 flukeFasciola hepatica – Sheep liver fluke

Pargonimus westermani – Human lung flukeSchistosomes – blood flukes

Where do adult schistosomes live?

Depends on species.Mansoni, japonicum, mekongi live in mesenteric

venulesMaematobium 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 miracidia2. Miracidia pentrate snails and mature to

cercariae3. Cercariae leave snail and penetrate host.

4. Migrate to lungs and liver and mature to adults5. 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 daysKatayama fever beginning 2-3 weeks after

exposureChronic schistosomiasis beginning 2+ years

What are cestodes

Tapeworms

List the cestodes

Taenia saginata – beef tapewormTaenia solium – pork tape worm

Diphyllobothrium latum – fish tape wormEchinococcus granulosus – dog tape worm

Describe the lifecycle of Taenia solium

1. Ingested eggs hatch in cattle2. Larva hatch in small intestines

3. Larva penetrate intestinal epithelium4. Larva migrate to the skeletal muscle to encyst

and develop to cystecerci5. 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.