# 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