Schistosomiasis

Question 1

What are the Schistosoma species that cause schistosomiasis and where are they located in the world?

Answer 1

• Schistosoma japonicum - China, the Philippines and Sulawesi
• Schistosoma mansoni - mainly found in Africa and Madagascar as well as parts of South America, the Caribbean and Arabia
• Schistosoma haematobium - throughout Africa, parts of Arabia, the Near East, Madagascar and Mauritius.
• Schistosoma mekongi - Thailand
• Schistosoma intercalatum - Congo, Guinea

Question 2

Describe the lifecycle of Schistosoma sp.

Answer 2

1. Schistosoma eggs are eliminated with feces or urine, depending on species.
2. Under appropriate conditions the eggs hatch and release miracidia
3. Miracidia swim and penetrate specific snail intermediate hosts.
4. In the snail, stages include two generations of sporocysts
5. And the production of cercariae.
6. Upon release from the snail, the infective cercariae swim, penetrate the skin of the human host image, and shed their forked tails, becoming schistosomulae.
7. The schistosomulae migrate via venous circulation to lungs, then to the heart, and then develop in the liver, exiting the liver via the portal vein system when mature.
8. & 9. Male and female adult worms copulate and reside in the mesenteric venules, the location of which varies by species (with some exceptions).
   A. S. japonicum is more frequently found in the superior mesenteric veins draining the small intestine
   B. S. mansoni occurs more often in the inferior mesenteric veins draining the large intestine image . However, both species can occupy either location and are capable of moving between sites. S. intercalatum and S. guineensis also inhabit the inferior mesenteric plexus but lower in the bowel than S. mansoni.
   C. S. haematobium most often inhabitsin the vesicular and pelvic venous plexus of the bladder, but it can also be found in the rectal venules.

The females (size ranges from 7–28 mm, depending on species) deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni,S. japonicum, S. mekongi, S. intercalatum/guineensis) and of the bladder and ureters (S. haematobium), and are eliminated with feces or urine, respectively image .

Question 3

Describe the egg of S. mansoni

Answer 3

• Schistosoma mansoni eggs are large (114 to 180 µm long by 45-70 µm wide)
• Have a characteristic shape, with a prominent lateral spine near the posterior end.
• The anterior end is tapered and slightly curved.
• When the eggs are excreted in stool, they contain a mature miracidium.

Question 4

Describe the egg of S. japonicum

Answer 4

• The eggs of Schistosoma japonicum are large and more rounded than other species, measuring 70-100 µm long by 55-64 µm wide.
• The spine on S. japonicum eggs is smaller and less conspicuous than other species.
• Eggs are shed in stool.

Question 5

Describe the egg of S. haematobium

Answer 5

• The eggs of Schistosoma haematobium are large (110-170 µm long by 40-70 µm wide)
• Bear a conspicuous terminal spine.
• Eggs contain a mature miracidium when shed in urine

Question 6

What snail is the intermediate host for S. mansoni?

Answer 6

Biomphalaria sp.

Intermediate host for S. mansoni..

Question 7

What snail is the intermediate host for S. japonicum?

Answer 7

Oncomelania sp.

Intermediate host for S. japonicum

Question 8

What snail is the intermediate host for S. haematobium?

Answer 8

Bulinus sp.,

Intermediate host for S. haematobium and S. intercalatum.

Question 9

How long to Schistosoma cercariae survive in water?

Answer 9

24-48 hours in freshwater.

If a definitive host is not found, they die

Question 10

How long is the prepatent period (infection to passage of eggs) for Schistosoma sp.?

Answer 10

4-12 weeks depending on species

Question 11

What is the final anatomical location of Schistosoma haematobium?

Answer 11

Venous plexus of the bladder and rectal venules

Question 12

What is the final anatomical location of Schistosoma japonicum?

Answer 12

Superior mesenteric veins of the small intestines

Question 13

What is the final anatomical location of Schistosoma mansoni?

Answer 13

Inferior mesenteric veins of the large intestines

Question 14

What type of cancer is associated with S. haematobium?

Answer 14

Squamous cell carcinoma of the bladder

Question 15

A long-term expatriate complains of itching 1 day after swimming in Lake Victoria in Uganda and presents to your clinic. What is the treatment of choice?

Answer 15

Return to clinic in 6 weeks

The most likely diagnosis is schistosomiasis. The itching would be dermatitis from the cercariae invading the skin. Persons who have prior exposure and sensitization may have immediate (transient) itching. Of note, Praziquantel treatment at this initial stage is ineffective, and the treatment should be delayed at least 6 weeks.

Question 16

How is schistosomiasis diagnosed in the lab?

Answer 16

Ova and parasite exam of either stool or urine

Question 17

What species of Schistosoma most commonly causes cerebral granulomatous disease?

Answer 17

S. japonicum

Cerebral granulomatous disease is caused by the eggs migrating away from Schistosoma japonicum. As the edges of S. japonicum are round, smaller in size and alrger in number, which may all lead to additional complications, they are likely to reflux further caudally through the spinal veins, which do not have valves.

Question 18

What is the treatment of choice for schistosomiasis? Which stage of the parasite are they effective against?

Answer 18

Praziquantel 40-60 mg/kg in 1 day

Effective against adult stage

Question 19

True or false: Infection with Schistosoma increases the carrier rate for Salmonella species.

Answer 19

True

Salmonella can evade antimicrobial treatment by living within the trematode.

Question 20

Which Schistosoma species are endemic in Africa?

Answer 20

• S. haematobium
• S. mansoni
• S. intercalatum

Question 21

Which species of Schistosoma may cause spinal cord lesions?

Answer 21

• S. haematobium
• S. mansoni

S. haematobium and S.mansoni may both present with transverse myelitis with flaccid paralysis. These rarely travel all the way up to the brain, due to their oblong shape and spinous process, which gets caught in the spinal veins.

Question 22

Which Schistosoma species are found in Asia?

Answer 22

• S. japonicum
• S. mekongi

Question 23

What are the features of acute schistosomiasis?

Answer 23

Katayama fever

• Fever
• Eosinophilia
• Diarrhoea
• Hepatomegaly
• Splenomegaly
• Cough and wheeze
• Cachexia
• Urticaria

Question 24

A university student returns from Uganda where she was working in the zoo in Entebbe on the edge of the Zika forest. She reports having been there during the rainy season. She frequently walked through knee-high water from floods due to rain and to the water rising from Lake Victoria. She presents to your clinic with fever, diarrhea and abdominal pain 3 weeks after returning to the U.S. She is coughing frequently during the exam. On physical exam, she has a palpable spleen. On CBC she has mild eosinophilia. She seems reliable and states that she faithfully took her antimalarials. What diagnosis is highest on your differential, given the above presentation?

Answer 24

Katayama fever

Katayama fever, as a form of schistosomiasis. You would also be right to include malaria on the differential, but malaria rarely presents with diarrhea, and cough also is less common. Additionally, a falciparum malaria would tend to present less than 3 weeks after exposure