Amoebiasis abscess

Entamoeba histolytica is an anaerobic rhizopod that occurs in tropical and subtropical areas. It can cause intestinal and extraintestinal manifestations. It is transmitted orally by ingestion of cysts that develop into trophozoites in the large intestine. Amebic trophozoites release several cytolytic factors, e.g. amoe-bapore, which enable the parasite to invade tissue. In intestinal amoebiasis, E. histolyticatrophozoites invade the intestinal mucosa, causing a form of ulcerative colitis with bloody and mucous diarrhoea. Extraintestinal manifestation of amebiasis results in abscess formation, usually in the liver but sometimes in the brain. 

Metronidazole is a nitro-imidazole. It is a mixed amoebicide, i.e. it acts at all sites of infection. It has to be activated in the parasite. By reduction in the amoeba of its nitro group reactive intermediates are formed, resulting in oxidative damage and ultimately cell kill. It is effective against many parasitic intestinal and tissue infections such as trichomoniasis, giardiasis and amoebiasis. It is the drug of choice for amoebic dysentery and amoebic liver abscess. 

Amoebiasis is an infectious disease caused by Entamoeba histolytica. It can cause asymptomatic intestinal infection, colitis (mild to moderate), dysentery (severe intestinal infection), ameboma, liver abscess etc. The drugs used in chemotherapy of amoebiasis are classified as in table 9.9.1. 

It is indicated in giardiasis, amoebic liver abscess, intestinal amoebiasis, trichomoniasis, ulcerative gingivitis, treatment and prophylaxis of anaerobic infections. 

Emetine and dehydroemetine are natural alkaloid obtained from Cephaelis ipecacuanha and synthetic analog respectively. They are effective against tissue trophozoites of . histolytica. It has no effect on cysts but effective in amoebic liver abscess also. It acts by inhibiting protein synthesis by arresting intraribosome translocation of tRNA-amino acid complex. Dehydroemetine is less toxic than emetine and very effective drug for tissue amoebiasis. It is more rapidly eliminated from the body than emetine. 

Symptoms of amoebic dysentery are associated with mucosal invasion and ulceration. Mucosal erosion causes diarrhoea, the severity of which increases with the level of invasion and colonization. Symptoms can also be affected by the site of the infection. Peritonitis as a result of perforation has been reported in connection with severe amoebic infection. Extra-intestinal amoebiasis is usually associated with liver infection, causing abscesses and/or enlargement. The abscess appears as a slowly enlarging liver mass and will cause noticeable pain. Jaundice may also occur due to blockage of the bile. Pleural, pulmonary, and pericardial infection results from metastatic spread from the liver, but can also manifest in other parts of the viscera or give rise to a brain abscess. However, these complications are uncommon. 

In practice, treatment of amoebiasis can be divided into treatment of bowel lumen amoebiasis, and tissue-invading amoebiasis. The bowel lumen infection, which is usually asymptomatic, may be in trophozoites form (non-infective) or in cysts form (infective) and treatment is directed at eradicating cysts with a luminal amoebicide (e.g. diloxanide). The tissue-invading amoebiasis (giving rise to dysentery, hepatic amoebiasis and liver abscess) must be treated with systemically active drugs (systemic amoebicides) active against trophozoites (e.g. metronidazole, tinidazole also, in dangerously ill patients dehydroemetine may be used, which is less toxic than the parent emetine (derived from ipecacuanha). Sometimes antibiotics (e.g. tetracycline) are used concurrently to stop opportunist infections. 

Amoebiasis is marked by two phases of the infection (a) intestinal amoebiasis characterised by dysentery and diarrhea, nondysenteric colitis, amoeboma (amoebic granuloma) and amoebic appendicitis and (b) extraintestinal amoebiasis (hepatic amoebiasis) marked by liver abscess [48],... 

Vanadium compounds containing thiosemicarbazide- and hydrazide-derived ligands, such as 26 and 27 in Figure 5.15, exhibit antiamoebic activity against Entamoeba histolytica. This water-borne amoebic protozoan parasitises the human intestines and in some cases other visceral organs, especially the liver. It is the aetiological agent of amoebiasis (also known as amoebic dysentery) and thus responsible for amoebic colitis and intestinal and liver abscesses. Symptomatic patients typically suffer from abdominal pain, diarrhoea... 

Antibody titers against Entamoeba histolytica by use of an enzyme immunoassay were strongly reactive in Amy Biasis blood. A diagnosis of amoebiasis was made. Her physicians started nitroimidazole amoebicides intravenously in a dose of 500 mg every 6 hours for 10 days. By the third day of treatment, Amy began to feel noticeably better. Her physicians told her that they expected a full clinical response in 95% of patients with amoebic liver abscesses treated in this way, although her multiple hepatic abscesses adversely affected her prognosis to a degree. 

Amoebiasis, due to infection with Entamoeba histolytica, is conveyed between humans by its cysts which are 10 microns in diameter. They survive well outside the body and are ingested in water and uncooked food. In the colon, the larger vegetative forms (trophozoites) emerge and cause chronic diarrhoea and, often, ulceration of the bowel wall. Unlike bacterial dysentery, this disease is seldom self-limiting without proper medication. Abscesses in the liver form a common complication. A ready cure can be effected with metronidazole (Section 6.3.3). 

Fig. 14.1. a Longitudinal and b transverse scans of right iliac fossa show asymmetric thickening of walls of the caecum, suggesting amoeboma in a patient with amoebic liver abscess, c Non-tender thickening of appendix (A) in amoebiasis. Cae-cal walls (CE) are also slightly thickened... 

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