S. mansoni

Definition

S. mansoni is a parasitic flatworm that causes schistosomiasis, a chronic and debilitating disease primarily affecting the circulatory and lymphatic systems. It is one of the most prevalent parasitic infections worldwide, particularly in tropical and subtropical regions.

5 Must Know Facts For Your Next Test

1. S. mansoni is one of the five major Schistosoma species that infect humans, with the others being S. haematobium, S. japonicum, S. intercalatum, and S. mekongi.
2. The life cycle of S. mansoni involves freshwater snails as intermediate hosts, where the parasite undergoes asexual reproduction to produce cercariae that can infect humans.
3. Infection occurs when cercariae penetrate the human skin during contact with contaminated freshwater, such as during bathing, washing, or agricultural activities.
4. After entering the body, the parasites migrate through the circulatory system, eventually settling in the mesenteric veins of the intestines or the vesical plexus of the bladder.
5. Chronic schistosomiasis caused by S. mansoni can lead to intestinal and hepatic complications, including liver fibrosis, portal hypertension, and increased risk of colorectal cancer.

Review Questions

• Describe the life cycle of S. mansoni and how it contributes to the transmission of schistosomiasis.
  • The life cycle of S. mansoni involves an aquatic snail as an intermediate host and humans as the definitive host. The parasite undergoes asexual reproduction within the snail, producing free-swimming cercariae that can penetrate human skin during contact with contaminated freshwater. Once inside the human body, the cercariae mature into adult worms that migrate to the mesenteric veins, where they produce eggs that can be excreted in the stool. The eggs hatch in freshwater, releasing miracidia that infect the snail host, completing the cycle. This complex life cycle allows S. mansoni to effectively propagate and spread schistosomiasis in endemic regions.
• Explain the pathological effects of S. mansoni infection on the circulatory and lymphatic systems.
  • S. mansoni infection can have severe consequences on the circulatory and lymphatic systems. The adult worms reside in the mesenteric veins, where they lay eggs that become trapped in various organs, including the liver, intestines, and bladder. This leads to a localized inflammatory response, known as granuloma formation, which can cause significant tissue damage and organ dysfunction. In the liver, the granulomatous reaction can lead to fibrosis and portal hypertension, potentially causing esophageal varices and gastrointestinal bleeding. In the intestines, the inflammation and fibrosis can result in bowel obstruction, bleeding, and increased risk of colorectal cancer. The involvement of the lymphatic system can also lead to lymphatic dysfunction and associated complications.
• Evaluate the global impact of S. mansoni infection and discuss potential strategies for prevention and control.
  • S. mansoni is one of the most prevalent parasitic infections worldwide, with an estimated 200 million people infected globally, primarily in sub-Saharan Africa, the Middle East, and parts of South America. The high prevalence and chronic nature of schistosomiasis caused by S. mansoni contribute to a significant global health burden, including reduced productivity, impaired childhood development, and increased susceptibility to other infections. Strategies for prevention and control of S. mansoni infection involve a multifaceted approach, including improving access to safe water and sanitation, promoting community-based health education, implementing mass drug administration with praziquantel, and developing effective vaccines. Successful control of S. mansoni infection requires a coordinated effort between public health authorities, healthcare providers, and affected communities to address the complex socioeconomic and environmental factors that contribute to the persistence of this parasitic disease.

Related terms

Schistosomiasis:

A parasitic disease caused by various species of Schistosoma flatworms, resulting in chronic inflammation and damage to the circulatory and lymphatic systems.

Cercariae: The free-swimming larval stage of Schistosoma parasites that can penetrate human skin and initiate the infection process.

Granuloma: A localized inflammatory response characterized by the formation of nodules around the Schistosoma eggs, leading to tissue damage and organ dysfunction.