Schistosomiasis
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Classification of Parasites
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Helminths
Nematodes (roundworms)
Intestinal
Blood and tissue
Cestodes (tapeworms)
Intestinal
Tissue (larval stage)
Trematodes (flukes/flatworms)
Intestinal
Liver/lung
blood
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Helminths
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Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Tissue Helminths
Nematodes
Trematodes
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosomes
Schistosomes are flat, fleshy leaf shaped worms, they posses two suckers – oral and ventral, a blind bifurcate intestinal tract, and prominent reproductive organs. Unlike the other Trematodes, schistosomes are not hermaphrodites, the males and females are separate individuals. They have a complicated life cycle starting with a snail as an intermediate host (some have 2 intermediate hosts).
The adult worms are long and slender (males are 6-12 mm in length; females are 7-17 mm in length) and can live in copula for 10-20 years within the venous system.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Transmission
Schistosomes are obligate intravascular residing organisms.
S. mansoni - inferior mesenteric veins of large intestine;
S. japonicum - inferior and superior mesenteric veins of small intestine;
S. haematobium - veins of urinary bladder.
The adult female schistosomes begin releasing eggs approximately 5-8 weeks after infection.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Transmission
When eggs are released, many are swept back into the circulation and lodge in the liver (S mansoni and S japonicum) or urinary bladder (S haematobium), while other eggs reach the lumen of the intestine and are passed out with the feces (S mansoni and S japonicum) or urine (S haematobium).
The eggs that are passed out in the urine or faeces, hatch in fresh water, releasing miracidia that enter the snail of the genera Bulinus, Biomphalaria or Oncomelania (intermediate host). The miracidia multiply asexually in the snail and eventually are released as infective cercariae in fresh water.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma snail (intermediate) host
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Bulinus
Biomphalaria
Oncomalania
Transmission 2
Humans acquire the infection when they come into contact with fresh water infested with the infectious cercariae. Cercariae are attracted to the warmth of a body and skin lipids and begin to burrow into exposed skin. These infective forms penetrate human skin and migrate through the lungs and the liver, before passing to their final habitat.
Within 30 minutes, the cercariae have penetrated the epidermis and transform into schistosomules, which enter the peripheral circulation, where they eventually become adults in the hepatoportal system or venous plexus surrounding the bladder.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Life Cycle
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Epidemiology
Schistosoma cause infection in about 200m people in 74 countries around the world, 85% of whom live in sub-Sahara Africa. Their distribution by species is :
S. Haematobium (Bilhazia) - Africa and middle east (most prevalent); S. mansoni - Africa and Latin America; S. japonicum – Pacific region
Two factors are responsible for endemicity—the presence of the snail vector and contamination of fresh water by human waste.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Pathogenesis
The most significant pathology is associated with the schistosome eggs, not the adult worms. Female schistosomes can lay hundreds or thousands of eggs per day within the venous system. The disease syndromes that characterize schistosomiasis coincide with the three stages of parasite development:
Cercariae penetrate the skin to cause a skin rash; Some weeks after infection, the mature worms deposit eggs, which may be accompanied by acute schistosomiasis (Katayama fever); Production of large numbers of eggs results in chronic granulomatous inflammation and fibrosis of the urinary tract or portal venous system.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Pathogenesis 2
In chronic cases, blood flow to the liver is impeded, which leads to portal hypertension, accumulation of ascites in the abdominal cavity, hepatosplenomegaly, and esophageal varices.
A granulomatous reaction surrounds the eggs and leads to fibrosis of the liver with S mansoni and S japonicum.
With S haematobium infections, there is urinary tract involvement: urethral pain, increased urinary frequency, dysuria, hematuria, and bladder obstruction leading to secondary bacterial infections.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Clinical Presentation
Clinically most infections are asymptomatic. Acute schistosomiasis (Katayama's fever) may occur weeks after the initial infection, especially by S. mansoni and S. japonicum.
Manifestations include fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia.
In endemic countries, clinical findings of acute schistosomiasis include an itchy rash (swimmer’s itch) that occurs within an hour after cercariae penetrate the skin, followed by headache, chills, fever, diarrhea, and eosinophilia 2-12 weeks after exposure.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Diagnosis
Microscopy to identify parasite eggs is the most practical method for diagnosis.
Stool sample examination should be performed when infection with S. mansoni or S. japonicum is suspected and urine sample examination should be performed if S. haematobium is suspected.
Special specimen prep techniques can increase diagnostic sensitivity.
Treatment: praziquantel, oxamniquine
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma haematobium
Infection occurs mainly in Africa, Asia, Portugal, India and Egypt. The reservoirs include monkeys, baboons and chimpanzees.
Schistomules develop in the liver and later migrate to the vesicle, prostatic and uterine plexus.
Eggs are deposited in the urinary bladder and are associated with squamous cell carcinoma of the bladder.
S haematobium eggs posses a terminal spine.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma haematobium
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma mansoni
This is the most widespread schistosome infection. It is found in Africa, Saudi, Brazil, Venezuela and West Indies. The reservoir hosts include primates, marsupials and rodents. The schistomules reside in the small branches of the inferior mesenteric vein near the lower colon.
Eggs are deposited around the bowel (giving rise to GI symptoms) and eggs can go to portal veins (giving liver symptoms).
The eggs has a sharp lateral spine.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma mansoni
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma japonicum
This infection is found only in the far Eastern nations of China, Japan, Philippines and Indonesia.
Known reservoirs include domestic animals like cats, dogs, cattle, horses and pigs.
The schistomules resides in branches of superior mesenteric vein around the small intestine, involving the GI, liver and brain.
Eggs are spherical with an inconspicuous spine.
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Schistosoma japonicum
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Thank you for paying attention
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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Any Questions?
Dr. Y. J. Peter (BMBCh, MSc, FMCPath.)
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