Helminthes- Schistosomes

Question 1

What are common names for schistosomes?

Answer 1

bilharzia or blood fluke

Question 2

How are schistosomes unusual trematodes?

Answer 2

• 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

Question 3

How are schistosomes spread?

Answer 3

eggs hatch in water, miracidium swims towards light (higher exposure during peak light hours)

Question 4

Which species cause intestinal schistosomiasis?

Answer 4

S. mansoni & S. intercalatum

Question 5

Which species cause urinary schistosomiasis?

Answer 5

S. haematobium

Question 6

Which species cause Asian intestinal schistosomiasis?

Answer 6

S. japonicum & S. mekongi

Question 7

Who is most affected by this disease?

Answer 7

mostly children because they plan in the water on hot days. anyone swimming during peak light/heat hours

Question 8

Which factor causes there to be an increase in parasites?

Answer 8

an increase in the number of intermediate hosts

Question 9

What are some symptoms?

Answer 9

• abdominal pain, cough, diarrhea, fever, fatigue
• eosinophilia
• hepatosplenomegaly
• mild itching and papular dermatitis
• genital sores (increases vulnerability to HIV infection)

Question 10

What is cercarial dermatitis?

Answer 10

skin rash upon massive penetration of skin by cercaria. cercaria lose their tails after penetrating the skin

Question 11

What is katayama fever?

Answer 11

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

Question 12

What causes hepatosplenomegaly?

Answer 12

an inflammatory immune reaction caused by deposition of eggs in tissues

Question 13

What are the consequences of chronic schistosomiasis?

Answer 13

direct morbidity (hematosplenomegaly) and additional morbidity (anemia + growth retardation)

Question 14

Which drugs are effective to kill larva and adult worms?

Answer 14

praziquantel and oxamniquine

Question 15

Why is using molliscicides not a good solution?

Answer 15

expensive, toxic to other living organisms

Question 16

Why is altering the aquatic environment not a good idea?

Answer 16

not economically practical & can damage fish populations & can promote other mollusc diseases

Question 17

What are some biological control solutions?

Answer 17

introducing a competitor snail, snail-eating fish, or growing certain aquatic plants

Question 18

Why is using the drugs not effective for the long term?

Answer 18

patient can always be reinfected upon exposure

Question 19

What are some other solutions?

Answer 19

have proper water-cleaning systems, infecting snails with other trematodes (prevents schistosome infection), find an effective vaccine

Question 20

What should the potential vaccine be targeting to optimize pathology?

Answer 20

the fecundity of the parasite so there is less spreading

Question 21

What stage of schistosomes causes pathology?

Answer 21

the eggs cause an inflammatory reactions and can suppress cell-mediated immunity

Question 22

Which parasite antigens are of current interest?

Answer 22

antigens expressed in the tegument

Question 23

What is a method that has been tested in mice to increase protection levels?

Answer 23

irradiated cercariae allow for immunization