Amoebiasis PDF

Amoebiasis It is caused by the protozoan parasite Entamoeba histolytica Intestinal Amoebiasis The infective stage: Quadri-nucleate (tetra-nucleate) cyst (cyst with 4 nuclei) The pathogenic stage: Trophozoite The sources of infection: Humans: Cyst passers (carriers & patients) Non-human primates (chi...

Amoebiasis It is caused by the protozoan parasite Entamoeba histolytica Intestinal Amoebiasis The infective stage: Quadri-nucleate (tetra-nucleate) cyst (cyst with 4 nuclei) The pathogenic stage: Trophozoite The sources of infection: Humans: Cyst passers (carriers & patients) Non-human primates (chimpanzees & baboons) The route of infection is the faecal-oral route (5 Fs) The infectious dose: >1000 cysts Vehicles of Mechanical Transport of Gastrointestinal lnfections (5 Fs) 1. Fingers 2. Flies 3. Foods 4. Fluids 5. Fomites Amoebic Dysentery Dysentery means bloody diarrhoea It is an acute disease The site of the disease is the large intestine 1 Mature infectious cysts 6 immature cysts 5 Immature cysts Some trophozoites invade blood vessels & carried in blood to Extra-intestinal organs (liver, lungs & brain) 7 -Some trophozoites transform into immature cysts. -Cysts & trophozoites are excreted in stool -Trophozoites die shorty (minutes) after excretion Flask shaped-ulcer 4 3 2 Cysts excyst in small intestine Clinical manifestations The incubation period ranges between 2 & 4 weeks About 90% of infected people are asymptomatic The patient typically presents with: 1. Abdominal pain 2. Tenesmus: urgent, painful & unsuccessful attempt to defecate (small volume of faeces) 3. Mucoid bloody diarrhoea (dysentery) Diagnosis -Clinical - Stool examination: Microscopic Stool antigen test Diagnosis Laboratory Investigations -Parasitological The stool is to be examined within the 1st hour of collection so as to find alive motile trophozoites otherwise to be preserved in polyvinyl alcohol Diagnosis -Macroscopically the stool contains mucus & blood -The pH of the stool is acidic in reaction -Microscopic Examination: -High number of pus cells and RBCs -Trophozoites are found in diarrhoeal stool only -Cysts are found in both diarrhoeal and formed stool To ascertain that the disease is amoebic dysentery, pathogenic trophozoites (with ingested RBCs) have to be detected in the diarrhoeal stool The prognosis of untreated patients -About 90% of patients recover completely within 3-7 days -Chronic carriage (cyst passers) - Fulminant amebic dysentery may be fatal - Perforation of the colon: may be fatal -Amoeboma -Extra-intestinal amoebiasis Treatment -Treatment of patients with clinical disease: The aim is to kill the trophozoites by metronidazole (1st choice) or tinidazole (2nd choice) -Treatment of cyst passers (to stop disease spread): The aim is to kill the cysts in intestinal lumen by paromomycin, iodoquinol or diloxanide furoate Amoeboma A mass of granulation tissues due to chronic infection by E. histolytica It is found mainly in the caecum & ascending colon It can be misdiagnosed clinically as carcinoma, tuberculosis, Crohn's disease, non-Hodgkin lymphoma…etc) Diagnosis By histopathological finding in a biopsy Treatment Metronidazole & paromomycin Prevention Improvement of personal and environment hygiene Provision of safe water for drinking & other domestic use Foods & fluids heating (water, milk…etc) at 50-56 o C Filtration of water (the filtres retain the cysts) Washing vegetables in clean running water Treatment of cyst passers NB: Water chlorination that kills enteric bacteria does not kill E. histolytica cysts Prevention Handwashing Defaecation in open Spaces is prohibited Safe disposal of excreta Flies fighting Safe water supply Extra-intestinal amoebiasis The trophozoites reach these sites by: A. Haematogenous spread B. Direct contact A. Haematogenous spread Some trophozoites in large intestine invade blood vessels and are carried in the blood causing: 1. Amoebic liver abscess: the commonest type of extra-intestinal amoebiasis 2. Amoebic lung abscess: also from liver abscess across the diaphragm 3. Amoebic brain abscess: rare but may be fatal NB: The term abscess here is a misnomer, because there is no pus Amoebic liver abscess - It occurs in about 5% of cases of intestinal amoebiasis - Commonly in the right lobe - Usually fast growing -Filled with liquefied hepatocytes & cell debris (necrotic cells) -There is no pus - Only trophozoites are detected (no cysts) Clinical manifestations The onset of the clinical manifestations may be acute or gradual The patient presents within 2-4 weeks of infection with: -fever - dull & aching abdominal pain in the right upper quadrant or epigastrium - tender hepatomegaly Diagnosis To be differentiated from pyogenic abscess & hepatocellular carcinoma Clinical Imaging Aspirate (anchovy sauce aspirate) Serological tests (ELISA). Microscopic examination of aspirate shows cell debris and trophozoites (no cysts). Nested PCR and monoclonal antibody methods. Amoebic liver abscess aspiration Rupture is a major complication Aspirate looks like Anchovy sauce: (a sauce made by smashing small fish). Aspirate Anchovy fish Amoebic brain abscess The onset of the clinical manifestations is abrupt & the progression is rapid that necessitates prompt diagnosis & treatment The clinical manifestations are non-specific depending on the number, location & size The presentation is as space occupying lesion/s Triad of amoebic brain abscess: 1. Fever 2. Headache 3. Focal neurological deficit MRI (magnetic resonance imaging) B. By direct contact Cutaneous amoebiasis: 1. Amoebic skin ulcer 2. Amoebic genital ulcer Cutaneous Amoebiasis Skin ulcer: The trophozoites reach the skin from the leakage when liver abscess is aspirated skin ulcer Cutaneous Amoebiasis Perianal & genital ulcers (labia, vagina & penis): The trophozoites reach these sites during unprotected anal intercourse with a patient with amoebic dysentery Genital ulcer Diagnosis of cutaneous amoebiasis - Clinical Microscopic detection of trophozoites in specimen from the edge of the ulcer Treatment of Extra-intestinal Amoebiasis The patient responds well to medical treatment The drugs used are metronidazole or tinidazole - In addition to abscess aspiration in case of large amoebic liver abscess (>5 cm)