Amoebiasis and giardiasis

Giardiasis and amoebiasis are primarily infections of the upper and lower gastrointestinal tracts, respectively. Giardiasis presents with gut upset ranging from acute watery diarrhoea with yellow, offensive stools and sulphurous eructation, to asymptomatic cyst excretion. Diarrhoea caused by Giardia lamblia persists for weeks to months, though with time the severity can decline and spontaneous eradication occurs. Cysts transmit the infection. They survive in the environment and in chlorinated domestic water supplies. Sand filtration removes cysts. Malabsorption occurs in symptomatic individuals. Diagnosis depends on finding the parasite, usually cysts in stools, but in acute cases trophozoites are seen in faecal smears. Treatment with tinidazole or another nitroimidazole compound is effective, eradicating the parasite and allowing gut abnormalities to resolve. Amoebiasis causes ulcerative changes in the bowel wall. Pathological changes are caused by cytotoxic effects of trophozoites on epithelial and submucosal tissue once invasion has occurred. Entamoeba histolytica trophozoites are found in scrapings taken from ulcerated or inflamed tissue and are seen as large cells with ingested RBCs in H&E-stained colonic biopsies. Treatment is with tinidazole or another nitroimidazole, with susequent diloxanide furoate to eradicate any residual luminal amoebae. Trophozoites spread via the portal vein to the liver, causing amoebic liver abscess that presents with fever, lethargy and pain. Amoebic serology is usually positive at presentation, and becomes positive within 1 week in those with negative serology initially. Ultrasonography is valuable in determining the location of the abscess and guiding aspiration for diagnosis or therapy, though the latter is not often needed.