BIOL123 - L9

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  • Created by: Katherine
  • Created on: 02-06-16 19:17
What type of parasite are schistosomes?
Trematodes
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What does schistosome mean?
Split body
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What are the 3 main types of schistosomes?
S.mansoni, S.haematobium, S.japonicum
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What are the 2 minor types of schistosomes?
S.intercalatum, S.mekongi
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What is the life cycle of the schistosome?
Eggs in faeces and urine, hatch releasing miracidia, miracidia penetrate snail tissue, sporocyts in snail (successive generation), cercariae released by the snail into water. These are free swimming and penetrate the skin.
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What happens once the cercariae penetrate the skin?
They lose tails and become schistosomulae. Circulation occurs. These migrate to portal blood in liver and mature into adults. The paired adult worms migrate to mesenteric venules of bowel/rectum, laying eggs that circulate to the liver and shed in st
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What is the life cycle within the human host?
The cercariae lose tails during penetration and become schistosomulae. Circulation occurs.These migrate to portal blod in lover and mature. The paited adult worms migrate to mesenteric venules of bowel/rectu,. Leying eggs that circulate liver, shed.
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What is the last stage of the human host cycle?
Venous plexus of bladder
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What are adult worms like?
Dioecious and sexually dimorphic, live within the venous system, form pair (the female living in the male's canal), live for 5 yeats.
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Where are S.haematobium found?
They live in the vesicle plexus surrounding the bladder - urinary schistosomiasis.
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Where are other schistosome species found in the human body?
They live in veins of the mesenteric plexus surrounding the small and large intestines - intestinal schistosiasis
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How many eggs do schistosomes release throughout adult hood?
300-3000 per days
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What is the period of time between infection of human host to beginning of eggs laying by adult worms
25 - 30 days
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The eggs of most species of schistosome have what?
A characteristic spine - this is important for species identification and diagnosis.
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What is the process of the schistosomes entering the snail?
Eggs in faeces and urine in the water. The eggs hatch releasing miracidia. The miracidia penetrate into snail tissue, and become sporocysts (successive generations) Cercariae released into water, penetrate skin of human.
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What conditions do Miracidia eggs hatch in?
Freshwater
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What are the features of Miracidia?
Free living and motile, infective for snails 6-8 hours after hatching. Able to locate suitable hosts using external stimuli such as light and snail derived chemicals.
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What are the features of sporocysts?
Inside snail tissue, the miracidium transforms into a non-motile primary sporocyst. Primary sporocysts produce generations of seconday sporocysts.
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What do each of the secondary sporocytes produce?
200,000 ccercariae- massive increase in reproductive potenetial.
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Why are cercariae released from the snail?
To infect the human host
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What are the features of Cercariae?
Released by the intermediate snail host, they are freel iving (survive up to 48 hours. They are very motile - using a forked tail to swim. Use water turbulence and skin derived chemical to locate humans. Penetrate the skin
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What do they become once they lose their tails?
Schistosomula
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What are the advantages of secondary hosts?
Increased reproductive potential - asexual reproduction can take place in alternative host. Increases range of parasie in space and time - infecting more than one host species parasite can survive when one host is scarce.
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What can an intermediate host do?
Channel the parasite towards its definitive host - intermediate frequently part of the definitive host's food chain.
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What happens to the Schistosome in the human host?
Cercariae lose tails during penetration and become schistosomsulae. Circulation occurs, cercariae migrate to portal blood in liver and mature into adults.
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Where do the paired adult worms migrate to?
Mesenteric venules of bowel/rectu, (laying eggs that circulate to the liver and shed in stools
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What are the features of Schistosomula?
Progress throug 3 developmental stages during migration, Skin
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Where do schistosomula mature into adult worms?
In the liver
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What happens once the schistosomes have matured?
They pair up and migrate to the final venous site.
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How many of cercariae that pnetrate the host reach maturity?
30-50%
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Untreated human schistosomiasis pass through 4 clinical phases, what are these?
Cercarial dermatitis, parasite maturation, established infection, Late stage infections
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What is associated with cercarial dermatitis?
Swimmers itch, caused by carcariae burrowing throguh the skin which causes and allergic reaction.
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What are the symptoms of swimmer's itch?
Occurs on secondary exposure to infection. Present
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What is associated with parasite maturation?
Known as acute schistosomiasis or katayama syndrom. It begins 2-8 weeks pi - resolves after several days or weeks. Usually mild and transient, but can be severe/ life threatening
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What are the symptoms associated with parasite maturation?
Dry couth, mild to moderate hepatosplenomegaly, pyrexia (fever), weight loss, giant urticarial - vascular reaction of the upper dermis - transien appearance of slightly elevated patched which are redder or paler than surrounding skin.
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What is associated with establisehd infection?
After resolution of acute symptoms, patients may become asymptomatic. Symptoms depend upon species of schistosome.
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What are the symptoms associated with S.haematobium?
Haematuria (blood in urine), dysuria (painful urination), abdominal pain, bladder inflammation.
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What are the symptoms associated with other species?
Abdominal pain, diarrhoae (may be bloody), hepatomegaly (with or without splenomegaly)
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What is assocaited with late stage infections?
This stage occurs after many years after primary infection and presents as one of several discrete syndroms.
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What is the syndrome associated with S.japoicum
Intestinal schistosomiasis
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What is the syndrome associated with S.mansoni
Hepatosplenic schistosomiasis, pulmonary schistosomiasis, CNS schistosomiasis.
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What is the syndrome associated with S.haematobirum
Urinary tract schistosomiasis
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What is the associated with abundant bladder grandulomas
Ureteric obstruction and renal failure
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What is Human schistosomiasis?
An immunopathological disease, caused by the host immune response directed against eggs which are trapped in the body. Over half the eggs laid by adult worms remain trapped in the body.
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What is the pathogenesis of chronic schisosomiais?
Egg deposition, inflammation, granuloma formation, obstruction of Urinary tract or portal circulation, fibrosis.
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What is granuloma formation?
It is concentric layers of cells forming distinct lesions.
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A response to antigens released by egg/miracidicum, the peak of the response is...
4-8 days after egg deposition
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What are the clinical symptoms of hepatosplenic disease?
Hepatosplenomegaly, portal hypertension, build up of pressure in the vein connecting the intestines and the liver due to cirrhosis of liver., ascites (fluid in the abdominal cavity)
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How is hepatosplenic disease diagnoised?
Presence of eggs in either stool or urine sample, other techniques include ultrasound, bladder or rectal biopsy, serological testing.
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What are the 3 factors responsible for maintaining transmission
Pollution of fresh water with excreta containing eggs, presence of suitable snail hosts, human contact with water infected with cercariae.
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Are there vaccines for schistosomiasis?
No
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Are there drugs to prevent it?
No
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Prevention:
Avoid swimming in freshwater in disease endemic countries, drink safe water, heat to 50'C for 5 mins or allow to stand for 24 hours.
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What is a treatment form Schistosomiasis?
Praziquantel
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What is the epidemiology of schistosomiasis?
Infections rise rapidly through childhood, it peaks at older children/young adults/ declines with old age. There is an age releated pattern of infectio (based on field, experimental and theoretical studies)
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What is the pattern?
Children become infected when they are old enough to play in water, due high exposure to water. They are non immune so rapidly become infected.
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Why does infection decrease with age?
Adults acquire more immunity but also are less likely to be in contact with the water.
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Immunity transplantation experiments:
If you give a money immunised against mouse proteins mouse proteins, it will be immune. But it isn't immune against monkey proteins.
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What is concominant immunity?
It describes the situation where a primary worm burden persists while the host is resistant to a secondary challenge.
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