Schistosomiasis Flashcards
What is schistosomiasis?
snail fever caused by blood flukes that live in veins of DH (>200 million people infected worldwide)
What are the 3 species in humans?
- schistosoma mansoni 2. haematobium 3. japonicum
What are the major differences between schistosomes & other trematodes?
- dioecious (separate male & female) 2. live in blood vessels 3. nonperculated eggs 4. no redia stage 5. no metacercarial stage 6. not food borne
Describe the life cycle of schistosome?
- egg 2. hatching 3. miracidium (male or female infects snails) 4. sporocyst -> daughter sporocysts 5. no rediae 6. cercaria 7. schistomsomula 8. adults
What happens during hatching?
stimulus is fresh water. cilia beat rapidly -> miracridium moves & spins. suture ruptures. miracidium escapes
Describes the parts of the cercaria head.
- glands: escape -> exit snail 2. post-acetabular: mucus -> attachment 3. pre-acetabular: enzymes -> penetration of host skin 4. head -> adjustment penetrating DH -> penetrates DH
Describe some characteristics of schistosomula.
in bloodstream migrate to lung live in pulmonary capillaries: feed on RBCs, grow/develop, systemic circulation -> young adults
Where do adults migrate to? What do they do here?
migrate to hepatic portal vein. reach sexual maturity, mate, pair migrates to venules of mesentery and live 10-30 years
Describe the morphology of adults?
- no phargnx -> ingest blood 2. dioecious - separate sexes 3. sexually dimorphic
Where is the gynecophoral canal found and what is its function?
inside the males it holds the female (shisto = split soma = body) allows for continuous mating
What happens to a female that is not paired to a male?
does not mature
Describe how the eggs of schistosome exit the body of the DH.
- pair migrated to smaller veins 2. female migrates to the smallest veins 3. lays eggs 4. miracidial SEA is released 5. stimulates granulome to form around egg 6. granulomas moves to gut/bladder & transports egg across wall & into lumen 7. granuloma cells disperse 8. eggs exit host (2/3 eggs don’t make it out)
What pathology results form penetration of cercariae into the DH?
cercarial dermatitis - allergic rxn, itchy skin
Where can the egg become trapped?
gut/badder wall, liver, spleen
What is the granulomatous response
SEA
What is SEA?
soluble egg antigen w pore in eggshell
What are the benefits and costs of the granuloma to the host?
protects the host but has costly pathology (ex: liver - Symmer’s pipestem)
What is Symmer’s pipestem fibrosis?
in the liver: poor circulation, hepatomegaly, normal function impared
How can kidney failure result from a S. haematobium infection?
eggs in urine and feces
What Sh?
bladder cancer: eggs in urine & feces & hematoria
What is Sm
colon cancer: eggs in feces
How are schistosome infections diagnosed?
eggs in urine and feces
What is hematuria?
blood in urine
What is the treatment for schistosomiasis and how does the drug work?
praziquantiel damages tegument -> more vulnerable to immune response
What does artemether do to the worms?
antimalarial drug that damanges tegument and cecum
What is the function of the glutathione-S-transferase in schistosomes? (GST)
parasite enzyme with detoxifying function. vaccine targets GST and reduces worm burden by 40-60%
Describe some methods of controlling schistosome infections.
- drugs to kill adult worms 2. sanitation 3. snail control 4. boots & rubber gloves 5. vaccine (GST) 6. Schistomiasis Control Initiative (Bill & Melinda Gates Foundation) gives of PZQ in sub-saharan Africa
