amoebiasis

introduction

infection caused by the amoeba Entamoeba histolytica
usually transmitted by the fecal-oral route
amoebiasis is estimated to cause 70,000 deaths per year world wide
it is often endemic in regions of the world with limited modern sanitation systems, including Mexico, Central America, western South America, South Asia, and western and southern Africa.

10% develop gastroenteritis after an incubation period usually 2-4 weeks, which ranges from mild diarrhoea to severe dysentery (severe ulceration of the gastrointestinal mucosal surfaces occurs in less than 16% of symptomatic cases)
it is an uncommon cause of traveller's diarrhoea

a granulomatous mass (known as an amoeboma) may form in the wall of the ascending colon or rectum due to long-lasting immunological cellular response
NB. inflammatory caecal area masses in returned travellers may be due to:
- ameboma
- helminthoma
- ascaris - usually pulmonary symptoms in 1st 2 weeks with cough, wheeze, maybe eosinophilia
- hookworm may cause eosinophilic enteritis
- strongyloidiasis may rarely cause eosinophilic oophoritis
- appendiceal abscess
- Crohn's disease
- malignancy
- etc.

10% of invasive cases result in spread to almost any organ, but in particular, the liver.
hepatic abscesses generally occur within 8-12 weeks of infection and favour the right lobe of the liver and are usually solitary abscesses
complications include:
- subdiaphragmatic abscess
- perforation of diaphgram to pericardium and pleural cavity
- perforation to abdominal cavital (amoebic peritonitis)
- perforation of skin (amoebic cutis)
generally have abnormal LFTs, raised inflammatory markers and if there is diaphragmatic irritation, may have R shoulder tip pain exacerbated by palpation of a generally non-tender or mildly tender RUQ
Ix: biliary ultrasound or CT abdomen

can occur at skin around site of colostomy wound, perianal region, region overlying visceral lesion and at the site of drainage of liver abscess

urogenital tract amoebiasis derived from intestinal lesion can cause amoebic vulvovaginitis (May's disease), rectovesicle fistula and rectovaginal fistula.

can occur from hepatic lesion by haemotagenous spread and also by perforation of pleural cavity and lung.
may cause lung abscess, pulmono pleural fistula, empyema lung and broncho pleural fistula.

amoebic liver abscesses can be difficult to differentiate from pyogenic (bacterial) liver abscesses based on clinical and imaging features alone, so serological or antigen testing is often necessary for definitive diagnosis
stool microscopy - cysts shed in stool but may need 3 samples to detect as shedding is not constant
serologic tests are available - 99% positive after 2wks of infection
PCR of blood, urine, or saliva can detect E. histolytica DNA
abscess aspirates:
- generally brown, thick fluid described as “anchovy paste”
- trophozoites seen in <20% of aspirates

infections occur in both the intestine and in the intestinal wall and/or liver.
Thus, two different classes of drugs are needed to treat the infection, one for each location.
abscesses may require aspiration , such as large abscesses (>5 cm) or those at risk of rupture