Nematodes

What are nematodes?

non-segmented roundworms: digestive system like a tube at both ends

What do most parasitic nematodes depend on?

Specific host species: cannot survive in any other organism

What are the 3 most common soil-transmitted helminths?

Roundworm, Whipworm, Hookworms

Who is most susceptible and why? (Pinworms)

Children: High co-infection rates and greater morbidity

What are the consequences of children developing worm parasites?

Childhood malnutrition, Physical growth retardation, and Deficits in cognitive & intellectual development

Steps of Nematode Reproduction

1. Enlargement by molting

2. Sexual reproduction: males are smaller than females

3. Offspring from females

What are the 3 different offspring of Nematodes?

1. embryonated eggs: containing embryo

2. unembryonated egg: further development in environment

3. ovoviviparous (live offspring; no egg)

Why do some nematodes wander?

mimics an intermediate host or migration and access to nutrients allows for faster growth

What is wandering?

a characteristic of nematodes moving away in search of resources

What is Enterobius vermicularis other name?

Pinworm

Pinworm hosts are

Humans

What is Trichuris trichura other name?

Whipworm

What is the transmission of Pinworms?

Orally: ingestion of embryonated eggs

What are Pinworms reservoir hosts?

None

What is the target tissue(s) of Pinworms: Enterobius vermicularis

Small intestine (for growth), Large intestine (target)

What are the aberrant sites of pinworms?

Liver, appendix, vagina

Where is transmission of pinworms common?

elementary schools & daycare

What is the pathology of pinworms?

Mild response in the gut

What is the clinical disease of pinworms?

Asymptomatic; intense anal itching → pruritus; secondary bacterial infection → cellulitis

What is pruritus?

an unpleasant itching sensation

What is retro-infection?

Eggs hatch on skin & larvae crawl through the anus into the colon & develop into adults

What is the aberrant pathogenesis of pinworms?

inflammation of the pelvis or granuloma in liver/appendix

What is the pathogenesis of pinworms?

adult females leave the anus at night due to a drop in body temp and release eggs, local irritation, retro-infection may occur

When does pathogenesis of pinworms begin?

embryonated eggs are swallowed

How does the immune system kill pinworms?

very hard; uses IgE and inflammation

How do we prevent pinworms?

we can’t

How do pinworms evade the immune system

no evasion

What treatment do pinworms have?

one drug treats the adults but no drug treats eggs

How do you diagnose pinworms?

Scotch tape test on anus

What is unique about pinworms?

minimal pathogenesis, body temperature dependent, rapid infectivity, gravid females, all stages develop in the gut

What is Trichuris trichiura known as?

Whipworm

Who are the whipworm hosts(s)?

Humans

How do you acquire whipworm?

Ingestion of embryonated eggs from the soil, must embryonate for ~18 days

Who are the reservoir host(s) for whipworm?

None

What is a syncytium?

a multinucleated cytoplasmic mass

What are the target tissue(s) of Whipworm?

Small intestine (for growth), Large intestine (target), epithelium of large

What is the pathology of whipworm?

prolapsed rectum

What is the pathogenesis of whipworms?

pore-forming protein to invade epithelium and form the host cell syncytium; extensive gut damage; chronic inflammation; blood loss (anemia)

Who typically get whipworm?

Children 

What is the clinical disease of harboring a whipworm?

Serious morbidity in children; Heavy infection leads to colitis and stunted growth; Chronic infection causes physical and cognitive deficits

How does the immune system kill whipworms?

Th2 response attempted (requires IL13 cytokine)

How does whipworm evade the immune system?

Adults secrete a protein that inactivates IL-13 needed for Th2 response, lowers antibody response

How is whipworm treated?

one drug

How do we prevent whipworm?

proper sewerage disposal; eggs are killed by 12 hrs of direct sunlight

What is unique to whipworms?

thin esophagus embedded in a host cell syncytium; helminthic therapy of Crohn’s disease

How do you diagnose whipworms?

Eggs in stool samples

What is helminthic therapy?

treatment of autoimmune disease by deliberate infection of parasitic worms

What is Ascaris lumbricoides known as?

Roundworms

Who are the hosts for roundworms?

Humans

Who is most affected by roundworms?

children; have higher worm burden

How do you acquire roundworms?

Ingestion of embryonated egg from soil/feces; eggs highly resistant to environmental conditions

What is the target tissue(s) of Roundworms?

Small intestine

What is the target tissue(s) of Aberrant Roundworms?

Pancreas, intestine/liver wall

What is chyme and who does this apply to?

Predigested food; Roundworms

What is peristalsis?

involuntary wave like muscle contractions

What is the pathogenesis of Roundworms

Adult worms impair physical growth; Malabsorption of fat & vitamin K; chronic intestinal inflammation → anorexia & cachexia; obstruction of intestine & bile ducts; holes in intestine/liver

What is the clinical disease of Roundworms in the migratory phase?

intense pneumonitis, can cause bronchospasm, liver enlargement

What occurs during aberrant migration with Roundworms?

Ascaris migrates from intestine into the liver → gallbladder → bile ducts

What is the clinical disease of roundworms in the adult phase?

Regurgitation and passage of adult worms; pokes holes in the intestine & liver; obstruct bile ducts & intestine; aberrant migration → migration into biliary tree, inflammation of the pancreas

What is bronchospasm?

A sudden constriction of muscles in the walls, causes difficulty breathing

What is biliary tree

branches of bile duct in the liver, bile aids in fat digestion

How does the immune system kill Roundworms?

Intense eosinophil infiltration, increased IgE during migratory phase, triggered by antigens released during molting

How do roundworms evade the immune system?

Secretes protease inhibitors and possesses a thick cuticle and unusual lipids to resist host digestive enzymes

How do you treat roundworms?

Drugs & surgery for intestinal block

How do you prevent roundworms?

Sewerage disposal

What is unique to roundworms

largest nematode to infect humans & wandering

How do you diagnose roundworms?

Eggs in stool sample or regurgitation of adults

What is rhabditiform larvae

early developmental larval stages of soil-borne nematodes which precede infectious filariform larvae.

What is filariform larvae

infective larva of nematodes that migrate through body to reach the intestine.

What is the other name for Ancylostoma duodenal?

Hookworm

What is the other name for Necator americanus?

Hookworm

What species of hookworm larvae is orally infectious?

A. duodenal

What species of hookworm larvae can undergo vertical transmission?

A. duodenal

What hookworm species is more virulent?

A. Duodenal

Who are the host(s) for hookworms?

Humans

How are hookworms transmitted?

actively penetrate through skin & soil-transmitted, orally

What is enteral?

intestinal stages of adult hookworms

What are the reservoir hosts of hookworms?

N/A

What is the target site(s) of Hookworms?

Small intestine, Skin, Lungs; A. duodenale can enter skeletal muscles and go dormant

What is the pathology of Hookworms?

anemia

What is the pathogenesis of Hookworms?

Larvae secrete metalloprotease causes hypersensitivity; adults suck blood and secrete anticoagulant; worms rupture RBCs and digest hemoglobin causes chronic blood loss; iron & protein deficiency anemia

What is the clinical disease of hookworms?

Asymptomatic; ground itch; pneumonia during migration; iron deficiency anemia; physical growth retardation; cognitive development deficit; spoon nails; yellow-green skin

How does the immune system respond to hookworms?

Migrating stages induce intense circulating eosinophilia

How do Hookworms evade the immune system?

Adults secrete an anticoagulant that blocks Xa & Vlla

How do you treat Hookworms?

Drugs; often toxic to children and pregnant women

How do you prevent Hookworms?

Sanitary disposal of human feces, health education, and footwear

What is unique to hookworms?

major iron deficiency, transmitted worldwide

How do you diagnose hookworms?

Eggs in stool

Who are the hosts for trichinella spiralis? 

Mammals

Who are the reservoir host(s) for T. Spiralis?

Pig

How do you transmit T. Spiralis?

Ingestion of raw/undercooked infected meat

What is the target tissue(s) of T. Spiralis?

small intestine epithelium, striated skeletal muscle cells (encysted nurse cell complex), migrating larvae: heart, brain, liver, and kidney

What is the pathology of T. Spiralis?

Heart failure and CNS damage

What is the pathogenesis of T. Spiralis during the enteral (intestinal) phase?

damage to the columnar epithelium; newborns induce inflammation; villi flattening = less absorbent; introduce bacteria to circulation

What is the pathogenesis during the parental phase of T. Spiralis?

dose-dependent damage; increased invasion; search for striated skeletal muscle to form nurse cell complex → damage to brain, liver, kidney & heart; penetration of non-striated cells causes death, cardiomyopathies & CNS abnormalities

What is the clinical disease of T. Spiralis during the early enteral phase?

inflammation of the stomach and intestines, diarrhea, abdominal pain & vomiting

What is the parenteral phase?

migration of newborn larvae from the intestine through the lymphatic and circulatory systems

What is the clinical disease of T. Spiralis during the parenteral phase?

myalgia, petechial hemorrhages, invasion of diaphragm muscles and CNS

How does the immune system kill T. Spiralis?

Only response is inflammation, Th2, mast cells, IgE

How does T. Spiralis evade the immune system?

switches the host cell metabolism and enables parasite survival for life