Helminthes- Schistosomes Flashcards
What are common names for schistosomes?
bilharzia or blood fluke
How are schistosomes unusual trematodes?
- have 2 intermediate hosts instead of 3
- cercaria, no metacercaria
- no redia stage
- are dioecious
- infect via direct penetration instead of being ingested
- they parasitize the intravascular niche
How are schistosomes spread?
eggs hatch in water, miracidium swims towards light (higher exposure during peak light hours)
Which species cause intestinal schistosomiasis?
S. mansoni & S. intercalatum
Which species cause urinary schistosomiasis?
S. haematobium
Which species cause Asian intestinal schistosomiasis?
S. japonicum & S. mekongi
Who is most affected by this disease?
mostly children because they plan in the water on hot days. anyone swimming during peak light/heat hours
Which factor causes there to be an increase in parasites?
an increase in the number of intermediate hosts
What are some symptoms?
- abdominal pain, cough, diarrhea, fever, fatigue
- eosinophilia
- hepatosplenomegaly
- mild itching and papular dermatitis
- genital sores (increases vulnerability to HIV infection)
What is cercarial dermatitis?
skin rash upon massive penetration of skin by cercaria. cercaria lose their tails after penetrating the skin
What is katayama fever?
a systemic hypersensitivty rxn agaisnt migrating schistosomes. occurs months after a primary infection, only upon a second exposure. most patients recover 2-10 weeks later
What causes hepatosplenomegaly?
an inflammatory immune reaction caused by deposition of eggs in tissues
What are the consequences of chronic schistosomiasis?
direct morbidity (hematosplenomegaly) and additional morbidity (anemia + growth retardation)
Which drugs are effective to kill larva and adult worms?
praziquantel and oxamniquine
Why is using molliscicides not a good solution?
expensive, toxic to other living organisms
Why is altering the aquatic environment not a good idea?
not economically practical & can damage fish populations & can promote other mollusc diseases
What are some biological control solutions?
introducing a competitor snail, snail-eating fish, or growing certain aquatic plants
Why is using the drugs not effective for the long term?
patient can always be reinfected upon exposure
What are some other solutions?
have proper water-cleaning systems, infecting snails with other trematodes (prevents schistosome infection), find an effective vaccine
What should the potential vaccine be targeting to optimize pathology?
the fecundity of the parasite so there is less spreading
What stage of schistosomes causes pathology?
the eggs cause an inflammatory reactions and can suppress cell-mediated immunity
Which parasite antigens are of current interest?
antigens expressed in the tegument
What is a method that has been tested in mice to increase protection levels?
irradiated cercariae allow for immunization
