4. SCHISTOSOMA 1. Morphology of Schistosoma • Common species affecting humans: o Schistosoma mansoni: Causes intestinal schistosomiasis. o Schistosoma haematobium: Causes urinary schistosomiasis. o Schistosoma japonicum: Causes intestinal and hepatic schistosomiasis. • Body Shape: o Unlike other trematodes, Schistosoma are elongate and cylindrical, resembling nematodes. o They are dioecious, meaning males and females are separate. • Male and Female Morphology: o Male: Shorter and thicker (~10-15 mm), with a gynecophoral canal (a groove that holds the female during mating). o Female: Longer and slender (~20 mm) to facilitate egg-laying. • Eggs: o Each species has characteristic eggs:  S. mansoni: Oval with a lateral spine.  S. haematobium: Oval with a terminal spine.  S. japonicum: Smaller and round with an inconspicuous spine. 2. Life Cycle of Schistosoma The life cycle involves two hosts: a definitive host (human) and an intermediate host (freshwater snail). Infection is acquired by skin penetration in contaminated water. A. In the Human Host (Definitive Host) 1. Infection: o Cercariae (free-swimming larval stage) in freshwater penetrate human skin during water contact. o Cercariae shed their tails and become schistosomula. 2. Migration in the Body: o The schistosomula enter the circulatory system, travel to the lungs, and eventually reach the liver for maturation. 3. Maturation and Pairing: o After 2-4 weeks, mature worms migrate to specific locations:  S. mansoni and S. japonicum: Mesenteric veins (intestinal blood vessels).  S. haematobium: Venous plexus of the bladder. 4. Egg Production and Excretion: o Female worms produce eggs, which are excreted through:  Feces (S. mansoni, S. japonicum).  Urine (S. haematobium). B. In the Environment and Intermediate Host (Snail) 1. Eggs Hatch into Miracidia: o In freshwater, eggs hatch into miracidia (ciliated larvae) within 1-2 days. 2. Infection of Snail: o The miracidia infect a specific snail species and undergo development into:  Sporocysts → Cercariae (infective larval stage). 3. Release of Cercariae: o Cercariae leave the snail and swim in freshwater, waiting to infect a human host. C. Life Cycle Summary Timeline • In Snail: 4-6 weeks from miracidia to cercariae. • In Human Host: 5-7 weeks for schistosomula to mature into adults and produce eggs. • Total Adult Life Span: Up to 5-10 years within human blood vessels. 3. Clinical Manifestations of Schistosomiasis The disease has acute and chronic phases, depending on the worm species and egg burden. A. Acute Phase (Cercarial Dermatitis and Katayama Fever) 1. Cercarial Dermatitis (Swimmer’s Itch): o A localized itchy rash at the site of cercariae penetration. 2. Katayama Fever (Systemic Hypersensitivity Reaction): o Occurs weeks after initial infection, often when the parasites migrate through the lungs and liver. o Symptoms:  Fever, chills, muscle pain, headache. Eosinophilia is common. B. Chronic Phase 1. S. mansoni and S. japonicum (Intestinal and Hepatic Schistosomiasis): o Chronic diarrhea, abdominal pain, and blood in stools. o Hepatosplenomegaly (enlarged liver and spleen) due to portal hypertension. o Liver fibrosis and cirrhosis in severe cases. 2. S. haematobium (Urinary Schistosomiasis): o Hematuria (blood in urine). o Chronic cystitis (bladder inflammation). o Increased risk of bladder cancer (squamous cell carcinoma). o In children, can cause hydronephrosis (kidney swelling). 4. Laboratory Diagnosis 1. Microscopic Examination of Eggs: o S. haematobium: Eggs in urine collected at midday. o S. mansoni and S. japonicum: Eggs in stool using concentration techniques (e.g., Kato-Katz method). 2. Serology and ELISA: o Detect anti-Schistosoma antibodies during early infections, when eggs may not yet be present in urine or stool. 3. Urine or Stool Antigen Tests: o Point-of-care tests detecting circulating antigens of Schistosoma (more accurate than antibody tests). 4. Ultrasound or CT Scan: o Helps detect liver fibrosis (in S. mansoni or S. japonicum) or bladder wall thickening (in S. haematobium). 5. Treatment of Schistosomiasis 1. Praziquantel (Drug of Choice): o Effective against all Schistosoma species. o Dosage:  S. mansoni and S. haematobium: 40 mg/kg once.  S. japonicum: 60 mg/kg in two divided doses. 2. Oxamniquine: o Alternative drug used in regions where praziquantel resistance is suspected (effective against S. mansoni). 3. Supportive Treatment: o Antipyretics and analgesics to manage fever and pain during the acute phase. o Management of portal hypertension and liver fibrosis (in severe cases). 4. Surgical Intervention: o In cases of severe bladder fibrosis or hydronephrosis, surgical management may be necessary. 6. Prevention and Control 1. Avoid Contact with Contaminated Water: o Avoid swimming or wading in freshwater bodies in endemic regions. 2. Snail Control Programs: o Use of molluscicides to reduce snail populations. 3. Mass Drug Administration (MDA): o Routine administration of praziquantel to at-risk populations in endemic areas. 4. Health Education: o Raise awareness about the dangers of schistosomiasis and the importance of avoiding exposure to infected water. 5. Improved Sanitation: o Prevent contamination of water bodies with human feces and urine.

 

4. SCHISTOSOMA

 

1. Morphology of Schistosoma

• Common species affecting humans:
• Schistosoma mansoni: Causes intestinal schistosomiasis.
• Schistosoma haematobium: Causes urinary schistosomiasis.
• Schistosoma japonicum: Causes intestinal and hepatic schistosomiasis.
• Body Shape:
• Unlike other trematodes, Schistosoma are elongate and cylindrical, resembling nematodes.
• They are dioecious, meaning males and females are separate.
• Male and Female Morphology:
• Male: Shorter and thicker (~10-15 mm), with a gynecophoral canal (a groove that holds the female during mating).
• Female: Longer and slender (~20 mm) to facilitate egg-laying.

 

• Eggs:
• Each species has characteristic eggs:
• S. mansoni: Oval with a lateral spine.
• S. haematobium: Oval with a terminal spine.
• S. japonicum: Smaller and round with an inconspicuous spine.

 

 

2. Life Cycle of Schistosoma

The life cycle involves two hosts: a definitive host (human) and an intermediate host (freshwater snail). Infection is acquired by skin penetration in contaminated water.

A. In the Human Host (Definitive Host)

1. Infection:
• Cercariae (free-swimming larval stage) in freshwater penetrate human skin during water contact.
• Cercariae shed their tails and become schistosomula.
2. Migration in the Body:
• The schistosomula enter the circulatory system, travel to the lungs, and eventually reach the liver for maturation.
3. Maturation and Pairing:
• After 2-4 weeks, mature worms migrate to specific locations:
• S. mansoni and S. japonicum: Mesenteric veins (intestinal blood vessels).
• S. haematobium: Venous plexus of the bladder.
4. Egg Production and Excretion:
• Female worms produce eggs, which are excreted through:
• Feces (S. mansoni, S. japonicum).
• Urine (S. haematobium).

 

B. In the Environment and Intermediate Host (Snail)

1. Eggs Hatch into Miracidia:
• In freshwater, eggs hatch into miracidia (ciliated larvae) within 1-2 days.
2. Infection of Snail:
• The miracidia infect a specific snail species and undergo development into:
• Sporocysts → Cercariae (infective larval stage).
3. Release of Cercariae:
• Cercariae leave the snail and swim in freshwater, waiting to infect a human host.

 

C. Life Cycle Summary Timeline

• In Snail: 4-6 weeks from miracidia to cercariae.
• In Human Host: 5-7 weeks for schistosomula to mature into adults and produce eggs.
• Total Adult Life Span: Up to 5-10 years within human blood vessels.

3. Clinical Manifestations of Schistosomiasis

The disease has acute and chronic phases, depending on the worm species and egg burden.

A. Acute Phase (Cercarial Dermatitis and Katayama Fever)

1. Cercarial Dermatitis (Swimmer’s Itch):
• A localized itchy rash at the site of cercariae penetration.
2. Katayama Fever (Systemic Hypersensitivity Reaction):
• Occurs weeks after initial infection, often when the parasites migrate through the lungs and liver.
• Symptoms:
• Fever, chills, muscle pain, headache. Eosinophilia is common.

B. Chronic Phase

1. S. mansoni and S. japonicum (Intestinal and Hepatic Schistosomiasis):
• Chronic diarrhea, abdominal pain, and blood in stools.
• Hepatosplenomegaly (enlarged liver and spleen) due to portal hypertension.
• Liver fibrosis and cirrhosis in severe cases.
2. S. haematobium (Urinary Schistosomiasis):
• Hematuria (blood in urine).
• Chronic cystitis (bladder inflammation).
• Increased risk of bladder cancer (squamous cell carcinoma).
• In children, can cause hydronephrosis (kidney swelling).

 

4. Laboratory Diagnosis

1. Microscopic Examination of Eggs:
• S. haematobium: Eggs in urine collected at midday.
• S. mansoni and S. japonicum: Eggs in stool using concentration techniques (e.g., Kato-Katz method).
2. Serology and ELISA:
• Detect anti-Schistosoma antibodies during early infections, when eggs may not yet be present in urine or stool.
3. Urine or Stool Antigen Tests:
• Point-of-care tests detecting circulating antigens of Schistosoma (more accurate than antibody tests).
4. Ultrasound or CT Scan:
• Helps detect liver fibrosis (in S. mansoni or S. japonicum) or bladder wall thickening (in S. haematobium).

 

 

 

 

 

5. Treatment of Schistosomiasis

1. Praziquantel (Drug of Choice):
• Effective against all Schistosoma species.
• Dosage:
• S. mansoni and S. haematobium: 40 mg/kg once.
• S. japonicum: 60 mg/kg in two divided doses.
2. Oxamniquine:
• Alternative drug used in regions where praziquantel resistance is suspected (effective against S. mansoni).
3. Supportive Treatment:
• Antipyretics and analgesics to manage fever and pain during the acute phase.
• Management of portal hypertension and liver fibrosis (in severe cases).
4. Surgical Intervention:
• In cases of severe bladder fibrosis or hydronephrosis, surgical management may be necessary.

 

6. Prevention and Control

1. Avoid Contact with Contaminated Water:
• Avoid swimming or wading in freshwater bodies in endemic regions.
2. Snail Control Programs:
• Use of molluscicides to reduce snail populations.
3. Mass Drug Administration (MDA):
• Routine administration of praziquantel to at-risk populations in endemic areas.
4. Health Education:
• Raise awareness about the dangers of schistosomiasis and the importance of avoiding exposure to infected water.
5. Improved Sanitation:
• Prevent contamination of water bodies with human feces and urine.