Pathogenesis

Pathogenesis

y are The organism enters the gut through food or water contam - inated with the cyst. In the small bowel, the cysts hatch and a large number of trophozoites are released and carried to the colon, where flask-shaped ulcers form in the submucosa. from The tr ophozoites multiply , ultimately forming cysts, which either enter the portal circulation or are passed in the faeces as an infective form that infects other humans as a result of insanitary conditions. Having entered the portal circulation, the trophozoites are filtered and trapped in the interlobular veins of the liver. They multiply in the portal triads, causing f ocal infarction of hepatocytes and liquefactive necrosis as a result of proteolytic enzymes produced by the trophozoites. The areas of necro - sis eventually coalesce to form the abscess cavity . The term ‘amoebic hepatitis’ is used to describe the microscopic picture in the absence of macroscopic abscess, a di ff erentiation only in theory because the medical treatment is the same. The right lobe is inv olved in 80% of cases, the left in 10% and the remainder are multiple. One possible explanation for the more common involvement of the right lobe of the liver is that b lood from the superior mesenteric vein runs on a straighter course through the portal vein into the larger lobe. in The abscesses are most common high in the diaphragmatic surface of the right lobe. This may cause pulmonary symptoms coloured, odourless, ‘anchovy sauce’-like fluid that is a mixture of necrotic liver tissue and blood. There may be secondary infection of the abscess, which causes the pus to smell. While pus in the abscess is sterile unless secondarily infected, trophozoites may be f ound in the abscess wall in a minority of cases. Untreated abscesses are likely to rupture. Chronic infection of the large bowel may result in a gran ulomatous lesion along the large bowel, most commonly seen in the caecum, called an amoeboma. Summary box 6.1 Amoebiasis: pathology /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

E. histolytica is the most common pathogenic amoeba in humans The vast majority of carriers are asymptomatic Insanitary conditions and poor personal hygiene encourage transmission of the infection In the small intestine, the parasite hatches into trophozoites, which invade the submucosa to produce /f_l ask-shaped ulcers in the colon In the portal circulation, the parasite causes liquefactive necrosis in the liver, producing an abscess, the commonest extraintestinal manifestation The majority of abscesses occur in the right lobe of the liver A mass in the course of the large bowel may indicate an amoeboma

Pathogenesis

y are The organism enters the gut through food or water contam - inated with the cyst. In the small bowel, the cysts hatch and a large number of trophozoites are released and carried to the colon, where flask-shaped ulcers form in the submucosa. from The tr ophozoites multiply , ultimately forming cysts, which either enter the portal circulation or are passed in the faeces as an infective form that infects other humans as a result of insanitary conditions. Having entered the portal circulation, the trophozoites are filtered and trapped in the interlobular veins of the liver. They multiply in the portal triads, causing f ocal infarction of hepatocytes and liquefactive necrosis as a result of proteolytic enzymes produced by the trophozoites. The areas of necro - sis eventually coalesce to form the abscess cavity . The term ‘amoebic hepatitis’ is used to describe the microscopic picture in the absence of macroscopic abscess, a di ff erentiation only in theory because the medical treatment is the same. The right lobe is inv olved in 80% of cases, the left in 10% and the remainder are multiple. One possible explanation for the more common involvement of the right lobe of the liver is that b lood from the superior mesenteric vein runs on a straighter course through the portal vein into the larger lobe. in The abscesses are most common high in the diaphragmatic surface of the right lobe. This may cause pulmonary symptoms coloured, odourless, ‘anchovy sauce’-like fluid that is a mixture of necrotic liver tissue and blood. There may be secondary infection of the abscess, which causes the pus to smell. While pus in the abscess is sterile unless secondarily infected, trophozoites may be f ound in the abscess wall in a minority of cases. Untreated abscesses are likely to rupture. Chronic infection of the large bowel may result in a gran ulomatous lesion along the large bowel, most commonly seen in the caecum, called an amoeboma. Summary box 6.1 Amoebiasis: pathology /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

E. histolytica is the most common pathogenic amoeba in humans The vast majority of carriers are asymptomatic Insanitary conditions and poor personal hygiene encourage transmission of the infection In the small intestine, the parasite hatches into trophozoites, which invade the submucosa to produce /f_l ask-shaped ulcers in the colon In the portal circulation, the parasite causes liquefactive necrosis in the liver, producing an abscess, the commonest extraintestinal manifestation The majority of abscesses occur in the right lobe of the liver A mass in the course of the large bowel may indicate an amoeboma

Pathogenesis

y are The organism enters the gut through food or water contam - inated with the cyst. In the small bowel, the cysts hatch and a large number of trophozoites are released and carried to the colon, where flask-shaped ulcers form in the submucosa. from The tr ophozoites multiply , ultimately forming cysts, which either enter the portal circulation or are passed in the faeces as an infective form that infects other humans as a result of insanitary conditions. Having entered the portal circulation, the trophozoites are filtered and trapped in the interlobular veins of the liver. They multiply in the portal triads, causing f ocal infarction of hepatocytes and liquefactive necrosis as a result of proteolytic enzymes produced by the trophozoites. The areas of necro - sis eventually coalesce to form the abscess cavity . The term ‘amoebic hepatitis’ is used to describe the microscopic picture in the absence of macroscopic abscess, a di ff erentiation only in theory because the medical treatment is the same. The right lobe is inv olved in 80% of cases, the left in 10% and the remainder are multiple. One possible explanation for the more common involvement of the right lobe of the liver is that b lood from the superior mesenteric vein runs on a straighter course through the portal vein into the larger lobe. in The abscesses are most common high in the diaphragmatic surface of the right lobe. This may cause pulmonary symptoms coloured, odourless, ‘anchovy sauce’-like fluid that is a mixture of necrotic liver tissue and blood. There may be secondary infection of the abscess, which causes the pus to smell. While pus in the abscess is sterile unless secondarily infected, trophozoites may be f ound in the abscess wall in a minority of cases. Untreated abscesses are likely to rupture. Chronic infection of the large bowel may result in a gran ulomatous lesion along the large bowel, most commonly seen in the caecum, called an amoeboma. Summary box 6.1 Amoebiasis: pathology /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF /uni25CF

E. histolytica is the most common pathogenic amoeba in humans The vast majority of carriers are asymptomatic Insanitary conditions and poor personal hygiene encourage transmission of the infection In the small intestine, the parasite hatches into trophozoites, which invade the submucosa to produce /f_l ask-shaped ulcers in the colon In the portal circulation, the parasite causes liquefactive necrosis in the liver, producing an abscess, the commonest extraintestinal manifestation The majority of abscesses occur in the right lobe of the liver A mass in the course of the large bowel may indicate an amoeboma