Ch. 16 - Schistosomes

Question 1

What are the characteristics of schistosomes?

Answer 1

• blood parasites –> feed on RBC
• dioecious
• cercariae penetrate skin of definitive host
• no metacercaria
• nonoperculate –> embryonated egg that hatches immediately after contacting water

Question 2

How does the female enter the male schistosome?

Answer 2

gynecophoral canal

Question 3

What 3 species infect humans?

Answer 3

1) S. mansoni
2) S. japonicum
3) S. haematobium

Question 4

What are the differences in the types of schistosomiasis?

Answer 4

S. mansoni + S. japonicum:
- hepatic/intestinal

S. haematobium:
- urinary

Question 5

What are the morphological differences between the 3 species that infect humans?

Answer 5

S. mansoni:
- 3-13 testes (male)
- grossly tuberculated tegument (male)
- long reunited ceca (male)
- short uterus (female)
- anterior ovary (female)
- vitelline glands (female)

S. japonicum:
- 6-8 testes (male)
- smooth tegument (male)
- short reunited ceca (male)
- long uterus (female)
- middle ovary (female)

S. haematobium:
- 4-5 testes (male)
- finely tuberculated tegument (male)
- intermediate reunited ceca (male)
- long uterus (female)
- posterior ovary (female)

Question 6

Where is S. mansoni located in the world?

Answer 6

south america, caribbean, middle east, and africa

Question 7

Where is S. japonicum located in the world?

Answer 7

china

Question 8

Where is S. haematobium located in the world?

Answer 8

africa + middle east + india

Question 9

What is the diagnostic stage?

Answer 9

eggs

Question 10

what is the infective stage?

Answer 10

cercariae

Question 11

What is the life cycle of schistosomas?

Answer 11

1) eggs shed in stools or urine
2) eggs hatch releasing miracidia
3) miracidia penetrate snail tissue
4) sporocysts in snail
5) cercariae released by snail into water + free swimming
6) penetrate human skin
7) cercariae lose tails during penetration + become schistosomulae
8) circulation
9) migrate to portal blood in liver + mature into adults

Question 12

Will cooking food prevent infection of schistosomas?

Answer 12

no

Question 13

What is the 2nd intermediate host of schistosomas?

Answer 13

none –> does not have one

Question 14

What is the location in the definitive host that S. mansoni stays?

Answer 14

inferior mesenteric veins –> drain to liver via hepatic portal vein

Question 15

What is the first intermediate host of S. mansoni?

Answer 15

Biomphalaria sp. (snails) –> aquatic

Question 16

How many eggs per day are released from the oviposition?

Answer 16

200 eggs/day/female

Question 17

what do granulomas do?

Answer 17

transport eggs to lumen in S. mansoni

Question 18

Miracidium penetrates Biomphalaria spp. snails, and does what?

Answer 18

gives rise to 2 sporocyst generations:
- mother (1) sporocyst
- daughter (2) sporocyst

Question 19

Which sporocyst produces cercariae by 30 days?

Answer 19

daughter sporocysts

Question 20

What type of environment are cercaria attracted to?

Answer 20

warmth + skin lipids

Question 21

Describe the “prepatent period”.

Answer 21

Adults migrate to mesenteric veins, produce eggs by 5-8 weeks post-infection

Question 22

Where are the adult S. japonicum located in the human body?

Answer 22

superior mesenterics

Question 23

What is the intermediate host of S. japonicum?

Answer 23

Oncomelania hupensis –> amphibious

Question 24

What is the egg production in S. japonicum?

Answer 24

2000 eggs/day

Question 25

Which schistosoma species has smaller eggs with small lateral spine?

Answer 25

S. japonicum

Question 26

Which schistosoma species has many reservior hosts (a zoonosis)?

Answer 26

S. japonicum

Question 27

What is the acute phase of pathogenesis in S. mansoni and S. japonicum?

Answer 27

- Katayama fever - PI - fever, rash, enlarged liver + spleen

Question 28

What is the chronic phase of pathogenesis in S. mansoni and S. japonicum?

Answer 28

- due to eggs - eggs washed into liver in portal circulation - soluble egg antigen --> granuloma --> fibrosis - hypersensitivity disease

Question 29

Describe Schistosomiasis due to S. mansoni and S. japonicum.

Answer 29

1) blockage of blood flow through liver (8% of cases) - hemorrhage 2) eggs enter systemic circulation - blockage of lung capillaries - CNS lesions 3) gastrointestinal hemorrhage + fibrosis

Question 30

Where are the adult S. haematobium located in the human body?

Answer 30

venous plexus surrounding urinary bladder

Question 31

What is unique about the egg morphology in the S. haematobium?

Answer 31

conspicuous terminal spine

Question 32

What is the intermediate host of S. haematobium?

Answer 32

Bulinus truncatus --> aquatic

Question 33

What is the pathogenesis of S. haematobium?

Answer 33

- granulomas around eggs in wall of bladder + ureters - damage to epithelium

Question 34

What does Schistosomiasis due to S. haematobium look like?

Answer 34

1) hematuria --> very dangerous 2) fibrosis, calcification of bladder wall + ureters 3) increased pressure on ureters + kidneys --> hydronephrosis 4) squamous cell carcinoma of the bladder 5) increased HIV transmission due to lesions in genital tract --> infertility high among women

Question 35

What does the spine of S. mansoni egg look like?

Answer 35

prominent lateral spine

Question 36

What does the spine of S. japonicum egg look like?

Answer 36

inconspicuous lateral spine

Question 37

What does the spine of S. haematobium egg look like?

Answer 37

terminal spine

Question 38

What is the prevalence of schistosomiasis worldwide?

Answer 38

240 million

Question 39

what is the morbidity of schistosomiasis around the world?

Answer 39

100-200 million w/symptoms + 20 million w/severe disease

Question 40

what is the mortality of schistosomiasis around the world?

Answer 40

200,000/year in sub-sahara africa alone

Question 41

Despite an effective drug, why is schistosomiasis still a problem?

Answer 41

1) increased population 2) increased irrigation 3) increased dams

Question 42

What 2 factors contribute to transmission of schistosomiasis?

Answer 42

1) contamination of snail habitats w/waste 2) human water contact

Question 43

How can schistosomiasis be controlled?

Answer 43

1) snail control --> molluscicides 2) chemotherapy --> praziquantel 3) education

Question 44

What is the immune response?

Answer 44

IgE/complement-mediated eosinophil killing

Question 45

What is the immunopathology?

Answer 45

immune response to eggs in liver, intestine, and bladder causes disease (hypersensitivity)

Question 46

Describe schistosome dermatitis.

Answer 46

- due to avian schistosomes - cercariae penetrate + die in skin --> inflammation --> accidental parasite - more severe response w/repeated exposures

Question 47

What does praziquantel do?

Answer 47

interferes w/ worm metabolism

Question 48

what does oxamniquine do?

Answer 48

works to paralyze worms

Question 49

what does metrifonate do?

Answer 49

interferes w/worm metabolism

Question 50

The black pigment in muscle is a response to _________ stage of schistosome.

Answer 50

metacercariae

Question 51

The 2nd intermediate host for many non-Schistosome flukes is:

Answer 51

fish

Question 52

What form is the Schistosome when it leaves the snail host?

Answer 52

cercaria

Question 53

What Schistosome species lives in Asia?

Answer 53

Schistosoma japonicum

Question 54

What Schistosome species lives in Brazil?

Answer 54

Schistosoma mansoni

Question 55

What Schistosome species lives in Egypt?

Answer 55

Schistosoma haematobium