Schistosomes

Question 1

Explain the life cycle of Schistosomes

Answer 1

Free swimming cercariae

• gets into blood supply to liver portal vein and then to mesenteric veins on to the small intestine, colon or bladder
• coat themselves with plasma protein to appear “self”

Question 2

What animal is the intermediate host for Schistosoma mansoni?

Answer 2

Non-segmented, specific snails

Question 3

What are the clinical manifestations of “swimmer’s itch”? Or dermatitis?

Answer 3

Penetrating cercariae

- papular pruritic rash (minor)

Question 4

What are the clinical manifestations of Acute Schistosomiasis (Katayama fever)

Answer 4

Large # of worms
Worms mature and deposit eggs
- fever, cough, hepatosplenomegaly, lymphadenopathy (serum sickness) with immune complex formation against egg Ag’s
- Eosinophils in blood due to tissue invasion
- generally resolves

Question 5

What are the clinical manifestations of chronic schistosomiasis?

Answer 5

Mature worms, heavy egg deposition
- fatigue, abdominal pain, diarrhea, hepatomegaly (enlarged liver), hematuria (blood in urine) hematemesis (cough up blood)

Question 6

How do you diagnose schistosomiasis?

Answer 6

Index of suspicion in those who have a travel history and fresh water swimming, rash, etc. Would be common in those areas

• eggs in stool or urine – quantify, repeat, concentrate if necessary
• Ab detection– check with CDC
• Eosinophilia (blood count) – not diagnostic, but suggestive if other things line up
• tissue bx may demonstrate eggs if stool/urine are negative
  
  • bladder (S. haematobium)
  • rectal for other species

Question 7

How do you treat Schistosomes? (flat or fluke)

Answer 7

PRAXIQUANTEL for all species – only actually treats active infection, not late sequelae
- consult ID

Question 8

How do you prevent Schistosomes?

Answer 8

• Avoid fresh water swimming in endemic areas.
• Rapid/vigorous toweling ???
• Reduce snail population (probably not)
• better sanitation

Question 9

What regions are endemic to schistosomes?

Answer 9

Africa, South America, the Caribbean, Middle East, and Asia

Question 10

How many people are infected with schistosomiasis? (According to MedScape)

Answer 10

207 million people, 85% of whom live in Africa are infected

Question 11

What is the infectious larvae form known as?

Answer 11

Cercariae - free swimming

Question 12

How can a chronic reaction occur?

Answer 12

Liver/intestines/bladder chronic inflammation with granuloma due to secondary reaction of tissues to eggs.
- can cause fibrosis/cirrhosis leading to portal hypertension or polyps/diarrhea if in the colon
- ascites (accumulation of fluid in the peritoneal cavity)
- eggs can lodge in lungs, spinal cord, etc.
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