Introduction to Parasitic Trematoda Quiz

Study Notes

Introduction to Parasitic Organisms: Schistosomiasis

Schistosomiasis is a parasitic disease caused by trematodes, specifically blood flukes, which are the most significant trematodes from a clinical point of view.
Approximately 250 million people are infected with blood flukes, and 600 million are at risk, with 5% of the world population having schistosomiasis.

Parasitic Trematodes: Classes and Characteristics

The phylum Platyhelminthes is divided into four classes: Turbellaria, Monogenea, Trematoda, and Cestoda.
The most significant trematodes from a clinical point of view are the blood flukes, which belong to the genus Schistosoma.

Schistosomiasis: Clinical Importance and Species

Three species of Schistosoma are of major medical importance: Schistosoma mansoni, Schistosoma japonicum, and Schistosoma haematobium.
Schistosomiasis, also known as bilharziasis or swamp fever, ranks second behind malaria as a cause of worldwide morbidity and mortality, resulting in approximately 800,000 deaths per year.

Symptoms and Diagnosis

People not previously exposed to schistosomiasis may develop flu-like symptoms, including dermatitis, fever, headache, persistent cough, myalgias, and malaise, known as "Katayama disease".
Infected individuals often develop heart, lung, and circulatory problems, with eosinophilia frequently present.
Chronic disease often produces bloody diarrhea, bowel obstruction, hypertension, and liver cirrhosis.
Diagnosis is confirmed by finding eggs in stool, urine, or rectal biopsy samples.

Life Cycle and Geographic Distribution

Schistosome eggs are released from the definitive host in feces or urine, and are ingested by snails, which act as intermediate hosts.
Free-swimming miracidia seek out and enter snail intermediate hosts, where asexual reproduction (sporocysts) occurs.
Schistosome cercariae emerge from snails and seek vertebrate hosts, penetrating host skin.
Schistosomules migrate via the circulation to the appropriate vascular sites, such as liver sinuses, intestinal and bladder veins.

Pathology and Complications

Adult schistosomes and eggs can cause serious liver cirrhosis and hepatosplenic disease.
Eggs and immature worms can also cause serious lung disease.
Adult schistosomes can remain in host tissues for 30 years or more, feeding on red blood cells and leaving a brown hematin pigment in tissues and phagocytic cells.
Schistosoma mansoni and Schistosoma japonicum can cause significant intestinal pathology, while S. haematobium can cause serious urinary complications.

Description

Test your knowledge on parasitic trematodes with a focus on Schistosomiasis and the four classes of flatworms within the phylum Platyhelminthes. Learn about Turbellaria, Monogenea, Trematoda, and Cestoidea.