BIOL123 - L8

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  • Created by: Katherine
  • Created on: 02-06-16 12:53
What is a roundworm?
A nematode
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What makes them dangerous?
They are able to cause infection and disease
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What are nemtodes?
They are a very successful group of animals. There are around 100,000 of the species described, but there are probably more.
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Where are they found?
The majority are free living and live in every conceivable environment. It is claimed that is all the matter in the world was desroyed except nematodes, you'd see the world in outline.
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Nematodes are also important in medical and ...
agricultural importance.
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What chatacteristics of nematods makes them successful parasites?
Their stylised body plan and life cycle is well suited for parasititic life. their biochemistry and physiology is very adaptble. They can survive a wide range of external conditions e.g. osmotic pressure, temp and ph.
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Continued:
They utilise a wide range of food sources and survive under both aerobic and anaerobic conditons. The tough cuticle of the nematode means that it can wihstand host immune responses.
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The nematde life cycle:
4 larval stages and 4 moults.
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Which stage is the infective stage?
L3 - this is when they are free living larvae.
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Microfilaria innoculate into bloodstream e.g.
Filarial worms
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What happens between the stages?
They shed the cuticle and re-synthesis another.
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Nematodes do not undergo sexual reproduction, what do they do instead?
Parthenogenesis. I.e. devleopment of gametes without fertilisation - it is rare in animal parasitic nematodes - instead its exposure.
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How many eggs does the Ascaris lay a day?
200,000
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Parasitism has arised on at least ... separated occassions in naematodes?
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What are gastrointestinal nematodes?
They live as adults in the intestine. They access the body easily as they are ingested. Their survival is favoured by the availability of high nutrition.
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How are gastrointestional nematodes transmitted?
Defecation.
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The intestinal species are the commonest, but not the most pathogenic. Which is?
The worm infection.
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What is polyparasitism?
It is when people harbour many different species at one time.
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What is health defined as?
The state of complete phycial, mental and social well being, and not merely the absence of disease or infirmity.
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How long do Male ascariasis grow to be?
10 - 30cm
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And females?
20 -35cm
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What is the appearance of the Ascariasis egg?
A thick shelled egg, up to 200,000 per day.
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Can eggs remain inactive for several months/years?
Yes
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Why is there a high prevalence of GI nematode infections?
There is widespread distrubution of nematodes in the environment,
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Why is there widespread distributino of nematodes in the environment...
Becuase eggs are resilient to harsh environmental conditions. Each parasite produces a high number of eggs. Poor socioeconomic conditions facilitate the spread of parasites e.g. people in environments where water is an open sewer. Lack of education -
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Where is Ascaris Lumbriocoides found?
Worldwide distribution but highest prevalence in tropical and subtropical reigions and areas with inadequated sanitation.
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What is the pathology associated with ingestion of ascaris lumbricoides larvae?
Server haemorahgic pneumonia, breathing difficulties, fever, highly allergenic = asthmatic attacks.
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The majority of the symptoms are associated with...
Ingestion and migration of larvae, with adult parasites in the intestine, due to wandering adults outside the intestine.
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Symptoms associated with adult worms in the intestine:
Digestive disorders (abdominal discomfort, nausea), symptoms depend on parasite burden (sever cases consist of many thousands of worms). Heavy infections contribute to malnutrition in the host if the host is undernourished. Blocked intestine
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Pathology associated with wandering audlts outside of the intestine:
Bile duct blockage = jaundice and interference in fat metabolism, appendix or break through intestinal wall - fatal peritonitis. Up the intestinal tract - vomitted or emerging through the nose. Suffocation.
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What is the life cycle of hook worms?
Eggs develop in feces, rhabditiform larva hatches, filariform larva, fitarigorm larva penetrate the skin. The adults are in the small intestine.
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Do hookworms have an intermediate host?
No, they have a direct lifecycle with no intermediate host and they live in the environemnt as free living larvae.
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How big are hookworm females?
9-13mm (smaller than asceris)
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How big are hookworm males?
7-11MM
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How long does it take for a hook worm egg to hatch?
1-2 days, they release rhabditiform larvae.
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What happens to the larvae after 5-10 days?
Two molts become filariform (third stage) larvae - these are infective- they directly penetrate through the skin.
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Pathology and consequences of hookworm infection:
Itching and rash at ste of larval penetration through skin - otherwise light infection may cause no symptoms.
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What are the symptoms if there is heavy infection:
Abdominal pain, diarrhoea, loss of appetite and wight loss - iron deficiency aneaemia caused by blood loss. The worms feed on the inestinal wall, causing blood loss.
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What else can hookworm infection result in?
Tiredness, breathing difficulties, enlargement of the heart and an irregular heartbeat.
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How are GI nematode infections diagnosed?
Eggs in stool sample - but this is not necessarily easy. Eggs and plant material look very similar.
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Who is most affected by Ascariasis:
Highest intensity infection primarily in school children.
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Hoow worms infect mostly:
Children, as they are less hygienic.
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Why is hookworm infection dangerous to pregnant women?
Results in anaema = low birth weight.
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What is the epidemiology of nematode infections:
Population dynamics of nematode parasites fundamentally idffferent from other infectious agents. E.g. most don't normally multiply witin an individual host. The intenstiy of infection is important.
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What did the Karkar study find?
The most heaviliy infected individuals are at greatest risk of morbidity and major source of infective stages.
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How can you prevent infection?
Avoid contact with soil contaminated with human faeces e.g. night soil. Wash hands with soap. Wash food. Don't defecate outside. Sewers
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What is another way of prevention?
Rockefellar sanitary commission -
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Card 3

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Card 4

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Nematodes are also important in medical and ...

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