Parasitology: Nematodes

What feature do Nematodes and Arthropods have in common?

undergo ecdysis

coelom of Nematoda

pseudocoelomate

Nematomorpha

phylum of horse-hair worms that is related to nematodes

Acanthocephala

spiney headed worms phylum- usually parasites of fish

Turbatrix acceti

vinegar eels, free-living nematodes

Caenorhabditis elegans

model organism in genetics- nematode- undergo Eutely

Eutely

when all organisms have the same number of cells throughout the entire life

• C. elegans

phasmid

post anal sensory organ of nematodes in the class Phasmidia

nematode body symmetry

bilateral

nematode reproduction

sexually dimorphic (male and female look different)- males have the curved end, dioecious

nematode male copulatory organ

spicule

nematode muscular system

longitudinal muscles only (why they “thrash” instead of “crawling” like annelids)

cuticle

flexible and resilient exoskeleton in nematodes

• permits locomotion and attachment to muscles

• confers environmental protection

• allows for growth after molting

alae

nematode expansions of the cuticle that helps maintain position in host intestinal tract

nematoe esophagus

muscular and granular- used to pump food into the body

nematode digestive system

complete digestive system, have mouths with lips

nematode excretory

renette gland in aquatic nematodes
fused renette glands in parasitic nematodes

What gives a nematode the round shape?

hydrostatic pressure in pseudocoel

general roundworm development

egg hatches into J1: molts to J2: molts to J3: molts to J4: molts to adult

ALWAYS 4 molts

Aphasmidia nematodes

• Trichuris trichiura

• Trichinella spiralis

• Trichuris suis

• Dioctophyme renale

Phasmidia nematodes

• Strongyloides tercoralis

• Ancylostoma duodenale

• Necator americanus

• Trichostrongyles

• Ascaris lumbriocoides

• Enterobius vermicularis

• Toxocara canis

• Anasakis

Trichuris trichiura common name

whipworm

Trichuris trichiura transmission

oral-fecal

Trichuiris trichiura eggs

barrel shape with 2 polar plugs

Trichuris trichiura life cycle

1. egg passed in the feces

2. larvae develops in the egg in the soil (must be warm, shaded and damp). Molts 1X in the egg

3. eggs ingested by human

4. egg hatches in small intestined (J2)

5. larvae penetrate intestinal villi and molt twice

6. larvae return to intestinal lumen and then cecum

7. mature/molt in cecum to adults

8. females release eggs in the feces

Trichuris trichiura epidemiology

1 billion infections world wide, 2nd most common in USA

Trichuris trichiura symptoms

• bloody stool

• ABD pain

• weight loss

• anemia

• rectal prolapse

Trichura trichiura diagnosis

eggs in the feces

Trichura suis

Trichuris spp in pigs.

used for Crohn’s Disease, ulcerative colitis and other inflammatory disorders as therpy (worm therapy)

Trichinella spiralis transmission

consumption of undercooked pork

Trichinella spiralis where are the adults and juveniles?

Juveniles: muscle cells

Adults: intestinal tracts

Trichinella spiralis life cycle

1. human/pig/bear eats infected animal

2. larva excysts from animal muscle in the small intestine

3. molts 4X in small intestine to adult

4. adults copulate in small intestine

5. larva deposited into intestinal tissue and carried to striated muscle with blood

6. larvae encyst in muscle cell and force muscle cell into a nursery cell

7. muscle cell eaten by next host

What do Trichinella spiralis juveniles do to a muscle cell?

force it from G0 to G2- making a nurse cell

Clinical phases of Trichinella spiralis

1. Penetration- adult enters mucse- mild symptoms

2. Migration- most severe- PNA, meningitis

3. Muscle Fiber penetration- pain, decrease blood pressure, decrease pulse, nervous disorders

Dioctophyme renale common name

Giant Kidney worm

Diotophyme renale hosts

intermediate: oligochaete (related to earthworm)

paratenic: frog, catfish

definitive: coyotes, canids, bears, mink

Dioctophyme renale life cycle

1. eggs released in urine

2. hatches in water

3. J1 penetrates oligochaete

4. molt twice

5. invade paratenic host (frog, catfish)

6. coyote ingests intermediate or paratenic host

7. migrates to hen liver then right kidney (and undergoes 2 molts)

8. adult worm in the right kidney

largest nematode to infect mammals

Giant Kidney worm (Dioctophyme renale)

Infective stage of most Phasmidia nematodes

J3

infective stage of Ascaris lumbricoides

J2

Rhabditiform juvenile

J1

Filariform

J3 (usually)- infective stage

Strongyloides stercoralis life cycle types

homogonic- exclusively parasitic (female only)

heterogonic - combination of parasitic and free-living generations (males and females)

Strongyloides stercoralis reproduction

parthenogenesis (reproduction of unfertilized eggs- no males needed)

Trichinella spiralis treatment

medication for adults in intestines, no treatment for encysted juveniles in muscles

Trichinella spiralis diagnosis

biopsy of muscle

Dioctophyme renale common name

Giant Kidney Worm

Diotophyme renale hosts

intermediate: oligochaete
paratenic: frog, catfish
definitive: coyote, bear, mink, sometimes dog & humans

Strongyloides stercoralis life cycle (basic)

homogonic life cycle- exclusively parasitic- female only"

heterogonic life cycle- combination of parasitic and free-living- males and females

Strongyloides stercoralis reproduction

parthenogenisis

Strongyloides stercoralis life cycle (detailed)

1. egg deposited in the intestine

2. rhabditiform larva hatches in the intestine

3. juvenile passed with feces to soil

4. in favorable conditions: 4X molts to free-living male or female→ reproduce-eggs released in the soil

5. in unfavorable conditions: 2X molts in soil- J3 penetrates host skin → enters bloodstream → heart/lung migration → 3rd molt in lungs then coughed up and swallowed → 4th molt in small intestine to adult → pathenogenesis & eggs depositied in intestine

6. : J1 penetrates mucosa→ molts 2X → enters bloodstream as J3 (repeats cycle)

Strongyloides stercoralis reservoir hosts

cats and dogs

Hookworm species

• Ancylostoma duodenale

• Necator americanus

Ancylostoma duodenale vs Necator americanus

Ancylostoma: Old World, has Teeth
Necator: New World, has plates

Hookworm eggs

• transparent

• embryonation of eggs requires warmth, shade and moisture in the soil

Hookworm lifecycle

1. egg passed in feces to soil

2. J1 hatches in soil- has long buccal cavity- feeds on bacteria and organic debree

3. 2X molts in soil to J3- nonfeeding stage, they tend to group together to increase chances of finding a host

4. penetrates skin of human

5. enters blood and lymphatic system

6. heart/lung migration

7. 3rd molt to J4 in lungs

8. coughed up and swalloed

9. 4th molt in small intestine

10. adult burrows into spaces between intestinal villi and holds on with teeth/plates

11. sexual reproduction

Hookworm pathology

• Cutaneous period- local irritation, inflammation, ground itch from bacteria

• Migration phase- heart/lung migration time- hemorrhaging if worm burden is high, dry cough, sore throat

• Intestinal phase- when hookworms in intestines and eating blood and mucosa- craving to eat dirt, developmental delays in children

hookworm disease severity depends on…

• worm burden

• species of hookworm (A. duodenale is more damaging)

• nutritional condition of host

hookworm diagnosis

eggs in feces

Trichostrongyles

parasite of grazing animals

Creeping eruption

animal hookworm in human host- juveniles wander under skin until they die

Ascaris lumbricoides life cycle

1. fertilized egg passed via feces to the soil

2. inside the egg, molts to J2

3. human ingests egg

4. J2 hatches in small intestine

5. penetrates mucosa → enters lymphatics and bloodstream → migrates to liver → to heart → to lung

6. 2X molts in lung

7. coughed up and swallowed

8. molts in small intestine to adult

9. copulation and egg release

Ascaris pathology

• Wandering adult females causes major problems

  • when no males or when overly crowded

  • they will migrate to all parts of the body

    • can cause bowel obstructions

Ascaris diagnosis

eggs in feces

Enterobius vermicularis common name

pinworms

Enterobius hosts

humans only

which nematodes have alae

Enterobius vermicularis

Enterobius vermicularis life cycle

1. eggs laid out of anus

2. molts to J3 in egg

3. ingested by human

4. hatch in small intestine

5. molt X2 and migrate to colon

6. copulation in colon-→ male dies and gravid female moves to rectum to lay eggs

Enterobius retroinfection

laid eggs out of the anus, go back up anus and infect same host

Enterobius vermicularis eggs

• extremely light-can be carried airborne

• flat on one end- look like a football

Toxocara canis

cosmopolitan parasite of dogs (humans accidental host)

Anasakis life cycle

1. eggs released in ocean

2. molt to J2 in egg

3. hatches in ocean and is free-swimming

4. ingest by crustacean

5. goes to hemocoel and molts to J3

6. marine fish (paratenic host) ingests crustacean

7. eaten by marine mammal (or human)

8. penetrates stomach of human or molts to adult in marine mammal intestine