Schistosoma spp.

Question 1

How is Schistosoma spp. classified?

Answer 1

metazoa: helminth (trematodes (flukes))

Question 2

What makes the Schistosoma spp. different from all the other trematodes

Answer 2

The sexes are separated in Schistosoma spp. - adults are divided into males and females

Question 3

Where do the adult Schistosoma spp. live in the host

Answer 3

In the blood vessels where the females release eggs (some eggs exit the host via urine/feces or stay become trapped in body tissue, causing immune reactions and progressive damage to organs)

Question 4

What is the life cycle of Schistosoma spp.?

Answer 4

1. eggs shed from infected humans in urine and feces and get into the water.
   S. mansoni, S. Japonicum, S. mekagi through feces, and
   S. haematobium through urine
2. Eggs hatch and release miracidia
3. Miracidia penetrate snail tissue
4. Sporocysts develop in snail (successive generation)
5. Free swimming cercariae are released from the snail into the water, they have a tail
6. Cercariae penetrate the human skin
7. Cercariae lose tails during penetration and become schistosomula
8. Schistosomulae go into the blood circulation (other organs?)
9. Migration to portal blood in lever and maturation in adult worms
10. Paired adult worms from the S. mansoni, S. japonicum, S. mekongi species migrate to the mesenteric venules of the bowel/ rectum laying eggs that circulate to the liver and shed in the stool
    Paired adult worm from the S. haemotobium species migrate to venous plexus of the bladder; eggs shed into urine

Question 5

What type of life cycle has Schistosoma spp and what are its hosts?

Answer 5

Indirect life cycle
Intermediate host: aquatic snail (different for each species)
Definite host: humans

Question 6

What is the infective form of Schistosoma spp.

Answer 6

Cercariae

Question 7

In what aspects do Schistosoma spp. differ?

Answer 7

1. intermediate host - each has their own snail species
2. the location in which the male and female adult worms copulate and reside
   - S. japonicum - superior mesenteric; draining the small intestine
   - S. mansoni - inferior mesenteric veins: draining the larger intestine
3. Location of eggs
   - S. mansoni, S. japonicum, and S. mekongi - lumen of the intestine
   - S. haematobium - bladder and ureters
4. Distribution
5. Disease they cause

Question 8

Describe the life cycle of Schistosoma spp in a snail

Answer 8

1. miracidia penetrate the soft tissue of a snail
2. Inside the snail, the miracidia loses their cillia and develop into mother sporocysts
3. The sporocysts rapidly multiply by asexual reproduction, each forming numerous daughter sporocysts
4. The daughter sporocysts move to the liver and gonads of the snail, where they undergo further growth
5. Within 2-4 weeks they undergo metamorphosis and give rise to fork-tailed cercariae
6. Stimulated by light, hundreds of cercariae penetrate out of the snail into the water and wait for a susceptible host

Question 9

What are other reserviors for Schistosoma spp.?

Answer 9

cattle, dogs, cats, rodents, pigs, horses and goats

Question 10

Which 3 species of Schistosoma spp. infected humans?

Answer 10

S. mansoni
S. haematobium
S. japonicum

Question 11

What is the incubation time of Schistosoma spp.?

Answer 11

14-84 days for acute schistosomiasis but many people are asymptomatic

Question 12

What symptoms are caused by Schistosoma spp.?

Answer 12

Many asymptomatic

Symptomatic
- Caused by inflammatory reactions by eggs
- Hypersensitivity of skin (swimmers rash), fever, cough, abdominal pain and
diarrhea
- Central nervous system lesions
- Cerebral granulomatous disease (caused by J. japonicum eggs in the brain)
- Granulomatous lesions around ectopic eggs in the spinal cord (caused by S. mansoni and S. haematobium)

Question 13

Where is Schistosoma spp endemic?

Answer 13

Worldwide, mostly in Africa

S. mansoni: sub- Saharan Africa and some South American countries (Brazil, Venezuela, Suriname) and the caribbean

S. haematobium: in Africa and pockets of the middle east

S. japonicum: China, Indonesia, the Philippines and Sulawesi

S. mekongi: Cambodia and Laos

S. guineensis: Central Africa

Question 14

Which species of Schistosoma spp is known as urogenital schistosomiasis?

Answer 14

Schistosoma haematobium (urinary and genital disease)

Question 15

How is Schistosoma spp. diagnosed?

Answer 15

Dipsticks - based on the detection of circulating Schistosoma antigens and CCA (circulating cathodic antigen) and CAA

Detection of parasite eggs in stool (S. mansoni and S. japonicum) or urine (S. haematobium)
ELISA - Antibodies and/or antigens in blood/ urine samples are also indications of an infection

biopsy of tissue