What is Schistosomiasis?
Schistosomiasis, also known as bilharzia, is a parasitic disease caused by flatworms of the genus
Schistosoma. These parasites infect humans through skin contact with contaminated freshwater. Upon entering the body, they migrate to blood vessels, where they mature and reproduce.
Histological Features of Schistosomiasis
Under the microscope, schistosomiasis is characterized by the presence of
Schistosoma eggs in tissues. These eggs can provoke significant immune reactions, resulting in granuloma formation. Granulomas are clusters of immune cells that attempt to wall off the eggs but can lead to tissue damage and fibrosis.
Commonly Affected Organs
Schistosomiasis predominantly affects the liver, intestines, and bladder. In the
liver, the disease can cause periportal fibrosis, a condition known as Symmer's fibrosis or "pipestem" fibrosis. In the intestines, granulomas and ulcerations can be observed. The bladder may exhibit inflammation, fibrosis, and sometimes even squamous cell carcinoma in chronic cases.
Histological Staining Techniques
Various
histological staining techniques are employed to identify Schistosoma eggs and tissue reactions. Hematoxylin and eosin (H&E) staining is commonly used to visualize the general tissue architecture and the presence of granulomas. Special stains like Ziehl-Neelsen and periodic acid-Schiff (PAS) can be used to highlight the parasitic eggs and surrounding fibrotic tissue.
Cellular Response to Infection
The immune response to Schistosoma eggs involves a range of cells, including
macrophages,
eosinophils, and
lymphocytes. These cells form granulomas around the eggs in an attempt to contain the infection. Over time, these granulomas can undergo fibrosis, leading to significant tissue remodeling and organ dysfunction.
Pathological Consequences
Chronic infection can lead to severe complications. In the liver, extensive fibrosis can result in portal hypertension, which may cause splenomegaly and ascites. Intestinal involvement can lead to obstruction, bleeding, and malabsorption. In the bladder, chronic inflammation and fibrosis can lead to obstructive uropathy and an increased risk of bladder cancer.Diagnostic Histology
Diagnosis of schistosomiasis through histology involves identifying the characteristic eggs within tissue samples. A biopsy of the affected organ, such as a liver, intestinal, or bladder biopsy, can reveal the presence of eggs and granulomas. This histological examination is crucial for confirming the diagnosis and assessing the extent of tissue damage.Histological Differentiation from Other Diseases
Histologically, schistosomiasis must be differentiated from other granulomatous diseases, such as tuberculosis and sarcoidosis. The presence of Schistosoma eggs is the key distinguishing feature. Additionally, the specific morphology of the eggs—such as their size, shape, and the presence of a terminal or lateral spine—can help identify the species of Schistosoma involved.Therapeutic Implications
Effective treatment of schistosomiasis involves antiparasitic medications like
praziquantel, which can kill the adult worms. However, histological changes such as fibrosis may persist even after the infection is cleared. Understanding the histological aspects of the disease is crucial for developing strategies to manage chronic complications and prevent long-term organ damage.
