Nematoda Flashcards
What are 7 types of parasitic nematode?
- filarial worms (Onchocerca, wuchereia, guinea worm)
- trichinella
- pin worm (Enterobius)
- hookworms (Necator and Ancylostoma)
- Ascaris lumbricoides
- toxocara canis
- anisakis simplex
Which nematodes have direct lifecycles?
Ascaris lumbricoides
Hookworms
describe the Ascaris lumbricoides life cycle
- Adult worms (-30cm long) in lumen of small intestine expel eggs into faeces into environment.
- fertilised eggs develop in environment
- Larval worm develops
- Egg swallowed by host and larval worm burrows into intestinal wall.
- Carried in bloodstream to organs, esp. lungs where they pass through wall of alveoli
- Irritant to host, coughed up and swallowed. Enter intestine and develop into adult.
Takes 2-3 months
How do Ascaris lumbricoides affect the host?
Eat host’s food, so major consequences if malnourished
Cause obstruction on intestine due to female moving to find mate
What allows transmission of Ascaris lumbricoides?
poor sanitation
200,000 eggs laid by females per day
What are two hookworm species?
Necator americanus, Ancylostoma duodenale
Where are hookworms common, and how are they transmitted?
In places where people walk over human waste. Broadly across tropics where high density of poor communities with out toilets and good sanitation.
STH - soil transmitted helminth infection.
describe hookworm life cycle
- Adults hook onto small intestine using teeth like features
- eggs pass out of host in faeces
- L2 larvae are free living in soil. eat bacteria
- L3 larva are the infective stage. Neg geotrophic, move towards warmth and vibration. Enter host feet and go directly into bloodstream.
- carried in bloodstream to lungs, coughed, swallowed and move into intestine.
what is dracunculus medinensis?
Guinea worm
Causes dracunculiasis
What is current state of guinea worm infection?
already reduced globally by 99% by Jimmy carter campaign.
hopefully soon eradicated
Only left in 3 countries: Chad, Ethiopia and S sudan.
Describe the Dracunculus medinensis life cycle
- Intermediate host = copepods. Humans drink water containing infected copepods.
- Copepods die, releasing L3 larvae which penetrate gut wall and enter tissues.
- Adult worms mate in thigh or armpit, male dies, female grown up to 1m long. migrate to limbs.
- L1 larvae (no eggs, ovoviviparous) released into water from blister
- L1 larvae easten by copepod, develop into L2and L3 in copepod.
How are adult guinea worms removed from human body?
Immerse limb with blister in water
Slowly pull worm out, stop when resistance to avoid breaking it. wrap around matchstick to keep tension and prevent it going back inside.
What is the species causing dog roundworms?
Toxocara canis
Describe toxocara canis life cycle
- Infective L2 larvae in eggs are ingested by dog from poo. Become dormant.
- Hormonal changes in pregnancy reactivate L2 larva
- puppies in utero infected via placenta
- larvae also passed to born puppies in milk
- in bitch and puppies larvae migrate from gut to trachea via lungs and liver. coughed up and swallowed. In gut, develop into l4 larvae and adults, release eggs, pass in feces.
What happens if a human ingests Toxocara canis L2 larvae?
Larvae migrate through tissues as VLM - visceral larva migrans. Become trapped in eye, causing ocular larva migrans. OLM
What is Filariasis?
Disease caused by infection of any roundworm that is vectorbourne
3 examples of Filarial infections
Onchocerca volvulus - Onchocerciasi, river blindness
Wuchereria and Brugia - Elephantiasis
Describe the lifecycle of Onchocerca volvulus
- Blackfly which take up L1 larvae from host blood
- Worms move through wing muscle in blackfly and develop into L3. L3 infects host through blackfly bite.
- L3 moult and L4 migrate through human body
- L5 adult worms form nodule and are encapsulated. sexual reproduction produced microfilariae which penetrate cornea of human eye causing blindness, or are taken up by blackfly.
Describe a circadian rhythm of microfillarial worms
move to peripheral tissues and blood at midnight, as people are asleep and more chance of blackfly bite
Where is river blindness found?
Riparian distribution of disease as blackfly live in fast flowing streams
What symptoms does onchocerciasis display?
Blindness
Itching where nodules are
allergic reaction to larval worms
How is Elephantiasis caused?
Infection of Brugia or Wuchereria, microfilarial worms transmitted by mosquito.
adult worms cause blockage of lymph ducts, resulting in severe swelling.
What is the control of Filariasis
GPLF - Global program to eliminate Lymphatic Filariasis
Aim by 2020, mass drug treatment and mosquito control.
Big pharma giving out free drugs to countries in need
Spray insecticide on rivers from helicopter to kill blackfly larvae
How is Trichinella transmitted?
- Larvae encyst in pig striated muscle.
- Ingestion of undercooked pork containing cyst.
3.Larva released in small intestine, adults develop in mucosal intestinal wall. females- 3mm, males- 1.4-1.6mm - Adults deposit larva in mucosa
- spread sporadically in circulation
Same lifecycle in pigs, rodent and human hosts
Where is Trichinella found?
Disease occurs in Arctic, wild Europe and in captivity.
Not routinely found in UK meat inspection but in Europ is epidemic.
Lifecycle of Anisakis simplex
- Marine mammals secrete unembryonated eggs in which L2 larvae form and hatch.
- free swimming L2 ingested by crustaceans, mature into L3.
- fish and squid eat crustaceans, larvae migrate to muscle tissues. Passed btw fish via predation.
- L3 larvae infective to humans and mammals. If fish host ingested by marine mammal, L5 adults develop and shed eggs.
If ingested by humans, worms cannot develop into L4. Stick onto oesophagus
