Trematodes, Platyhelminthes (Flat Worms)

Question 1

Schistosoma characteristics

Answer 1

Hermaphodites, hypodermic impregnation anywhere in body
Monstome: oral sucker only, distome: oral sucker and ventral acetabulum, amphistome: oral sucker and posterior acetabulum
(Acetabulum adhesion only, sucker openings into body
Feeding/digestion: tissue drawn into oral sucker, eroded, blood/cytoplasm pumped into body, digestive tract variable branched (monocladida: one tube, dicladida, polycladida
Snails intermediate host, humans definitive

Question 2

Special features of life cycle

Answer 2

Miracidia: ciliated, penetration gland and enzymes to enter snail, contains sporocytes (contain daughter cysts) with circae
No rediae in shistosomes
Metacercariae: resting stage
Can go to metacyst, hibernation if no host found

Question 3

Schistosoma Infection/symptoms

Answer 3

Schistosomiasis
Most asymptomatic
Skin penetration by cercariae leaves small hemorrhage with localized edema/itching, resolves
Next 3 weeks transient toxic/allergic rxns: fever, malaise, vague intestinal complaints, cough, spitting up blood, acute hepatitis
Egg laying in intestinal veins 1-3 months, fever, skin pustules, abdominal pain, liver tenderness, dysentery
Chronic phase: gradual, , rose-thrones eggs in small vessels close to lumen of intestine
Eggs contain miracidia, may stimulate abscess formation, can get washed back to liver, forming granulomas
Hepatosplenic schistosomiasis: liver blockage, leads to portal HTN, left lobe becomes grossly enlarged, spleen can become enlarged, varices form
Intestinal schistosomiasis: abdominal cramps, tenderness, bloody stools, formation of polyps, wt loss, anemia
Schistosomiasis dermatitis: swimmers itch, results from schistosomes cercariae that normally infects birds, superficial red spots

Question 4

Schistosoma treatment

Answer 4

Praziquantel, one dose