Schistosomiasis Flashcards
Breifly describe life cycle of Schis
Eggs excreted by humans into water. Eggs hatch, releasing miracidia which enter snail tissue. Succesive gens of sporocysts in snail. Free swimming Cercariae released by snails into water. Penetrates humans (losing tail). Becomes schistomulae. Circulates, eventually migrating in portal blood to liver . Mature into adults. Adults reproduce, lay eggs in bowel/rectum/bladder. Restart
Describe the anatomy of the cercariae
Oral sucker with ducts
Pre-and post acetabular glands (contents lost at penetration)
Glycocalyx (tail - lost at pen.)
Released material taken up by pahgosome prior to peresentation with MHCII
Describe the consqeuences of Schis infection
Eggs released by adults lodge in liver/intestines
Host mounts intense inflammatory granuloma around egg (resultant tissue damage leads to heptomegaly/splenomegaly)
In majority of patients (>90%) immune hyper-responsiveness is modulated and granulomas reduce in size
Disease can be largely asymptomatic
Describe Chemotherapy options for schis and give problems
One drug - Praziquantel (destabilies tegument membrane of adult worms)
Dose: 40-60mg/kg at $1 per tablet
80% cure rate with 1 dose
Exposes worm surface to Ab
Problems:
only 1 drug
only kills adults
Dead bodies hang around
Evidence of drug resistance in lab and field (<30%)
ineffective in high prevelance areas
does not prevent reinfection, induce protective immunity , or kill juvenile worms
Ineffective if species is zoonotic
Relies on good immune response (HIV co-infection not cool)
Describe current vaccine status
1980-90’s were 6 leading vaccines originating from expression cDNA library clones. NOne were found to be effective in clinical trials
ShGST (Bilhvax) undergoing phase II clinical trials (targets only S. haematobium)
What is the tegument
Membranocalyx
Surface adapted to facilitate immune evasion
Made of 2 opposed lipid bilayers (membranocalyx and plasma membrane)
