Schistosomiasis infects approximately 200 million persons and kills approximately 280,000 annually. Most of the mortality comes from hepatic granulomas and fibrosis Schistosoma japonicum and Schistosoma mekongi in East Asia
Pathogenesis Transmitted by freshwater snails Infectious schistosome larvae (cercariae) swim through fresh water and penetrate human skin Schistosomes migrate into the peripheral vasculature, traverse to the lung, and settle in the portal or pelvic venous system Females produce hundreds of eggs per day, around which granulomas and fibrosis form. Some schistosome eggs are passed from the portal veins through the intestinal wall into the colonic lumen, are shed with the feces
Schistosome life cycle.
Morphology Penetration of the skin by cercariae caused a transient local inflammatory reaction Cercarial dermatitis Lesions caused by adult schistosome and their metabolic products Lesions caused by eggs: the main lesion of Schistosomiasis
Morphology Acute egg nodule (eosinophilic abscess) In schistosomiosis, eggs surrounded by many eosinophils and like abscesses. Chronic egg nodule (pseudotubercle) In schistosomiosis, eggs surrounded by epithelioid cell, multinuclear giant cell; eggs are often necrotic or calcified. This structure is like that of a tubercle. It is a granuloma.
Schistosoma mansoni granuloma with a miracidiumcontaining egg (center) and numerous, adjacent, scattered eosinophils.
Lesions in other organs Colon inflammatory patches or pseudopolyps may form in the colon Liver pipe-stem fibrosis (massive fibrosis around major portal tracts) Spleen splenomegaly Heterotopic Schistosomiasis lung cerebrum other organs
Pipe-stem fibrosis of the liver due to chronic Schistosoma japonicum infection.
Schistosoma haematobium infection of the bladder with numerous calcified eggs and extensive scarring.
Clinical Course Portal hypertension with abdominal distention, hepatosplenomegaly, pedal edema, pallor, distended abdominal veins, and ascites Intestinal polyposis with heme-positive stool, pallor, and signs of malnutrition CNS symptoms, including focal neurological findings, seizures, and spinal cord lesions Renal failure with anemia and hypertension Cor pulmonale with signs of right heart failure Genital lesions including ulcer or nodular lesions of cervix, valva, or vagina or vesicovaginal fistula
Amoebiasis Entamoeba histolytica (ameba) is a dysentery-causing protozoan parasite spread by fecal-oral transmission. infects approximately 500 million persons in developing countries resulting in approximately 40 million cases of dysentery and liver abscess
Pathogenesis E. histolytica cysts A chitin wall and four nuclei The infectious form because they are resistant to gastric acid Cause epithelial cell apoptosis Invade the crypts of colonic glands Burrow into the lamina propria
Amebiasis from infection with Entamoeba histolytica is diagnosed here on trichrome stain of a stool specimen.
Entamoeba histolytica in colon. High-power view of the organisms. Note some of the organisms ingesting red blood cells.
Infection by Entamoeba histolytica occurs by ingestion of mature cysts
Morphology Most frequently involves the cecum and ascending colon, followed in order by the sigmoid, rectum, and appendix Flask-shaped ulcer with a narrow neck and broad base Extensive liquefactive necrosis
Amebic Colitis
Flask-shaped ulcer of Amebic Colitis
Flask-shaped ulcer
Amebic liver abscess In about 40% of patients with amebic dysentery, parasites penetrate splanchnic vessels and embolize to the liver A scant inflammatory reaction at their margins and a shaggy fibrin lining Abscesses are filled with a chocolatecolored, odorless, pasty material.
Gross pathology of liver containing amebic abscess
Gross pathology of amebic abscess of liver. Tube of "chocolate" pus from abscess.
Amebic abscess of liver, gross.
Clinical Course Abdominal pain, bloody diarrhea, or weight loss. Occasionally, acute necrotizing colitis and megacolon can occur Rarely, amebic abscesses reach the lung and the heart by direct extension from the liver or spread from the liver through the blood into the kidneys and brain.
Necrotizing amoebic meningoencephalitis involving the cerebellum (organism highlighted by arrow).