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tx
digestive system
intestinal parasites
diagnoses
definition and etiology
definition:
infection of the colon by a protozoal parasite; two examples are amebiasis (Entamoeba histolytica) and giardiasis (Giardia lamblia)
etiology:
amebiasis: This disease may be asymptomatic or may cause diarrhea ranging from mild to severe (dysentery). Entamoeba histolytica has 2 forms, the motile trophozoite and the cyst. The trophozoite is the parasitic form that dwells in the bowel lumen where it lives on bacteria and/or tissue. When diarrhea occurs, the unchanged trophozoites can be recovered from the stool. They are extremely labile outside the intestine, dying quickly. When they pass from the intestine in normal stool, they usually enter into their cyst form, which is very resistant to environmental change and is how they spread from person to person through food or water. The spread is either direct (e.g. among children in day-care centers or homosexuals practicing anal-oral sex) or indirect (e.g. from contaminated food eaten by travelers). In the U.S. the spread is usually direct and the infection rate is 1-5%. In some areas of the world where sanitation is very poor, the infection rate may increase to 50%. Amebiasis can result in intestinal ulceration and the spread of E. histolytica through the portal venous system to the liver, and from there to the pleura, right lung and pericardium.
giardiasis: also frequently asymptomatic, although symptoms may range from flatulence to malabsorption. The organism contains a central sucker, with which it adheres to the mucosa of the duodenum and jejunum in its trophozoite form. It is found in normal stool in its cyst form, which is resistant to environmental changes. Like E. histolytica, it is spread by the fecal-oral route, either directly or indirectly. It is seen worldwide and is now the single most frequent cause of waterborne-induced diarrhea in the U.S. It is common in travelers, hikers, homosexuals, and children in day care centers.
signs and symptoms
signs and symptoms: amebiasis: most patients are asymptomatic because of the infrequency of tissue invasion; symptoms develop only when tissue invasion occurs
alternating diarrhea and constipation
flatulence
cramping abdominal pain
liver and ascending colon tender to palpation
stools may contain blood and/or mucus
amebic dysentery (more severe form, usually seen only in the tropics): episodes of frequent fluid or semifluid stools; stools often contain blood, mucus flecks; slight fever occasionally seen; emaciation and anemia can worsen between attacks, although intestinal symptoms decrease to abdominal cramps and semisolid stools
lab findings:
(+) trophozoites, cysts, or eggs in stools: may require up to 6 specimens
(+) biopsy of intestinal lesions
(+) serologic tests
with liver abscess: possible (+) x-ray, (+) radioisotopic liver scan, (+) ultrasound scan, increased ESR and alkaline phosphatase
increased eosinophils with worms
purged specimens are best for recovery of organisms
signs and symptoms: giardiasis: most patients are asymptomatic or only mildly affected
recurring anorexia, nausea, eructation/flatulence, epigastric pain, abdominal cramps, diarrhea
malabsorption causing weight loss and bulky, greasy, malodorous, occasionally foamy stools which float
lab findings:
(+) organism (usually cysts) in stool: may need up to 6 specimens
(+) examination of duodenal contents for trophozoites (string test)
(+) serologic tests
course and prognosis
Complications include bowel perforation, abscess, hemorrhage, pulmonary and pericardial infection, cutaneous ulceration, irritable bowel syndrome and rarely, intussusception.
For amebiasis, the most common extraintestinal complication is hepatic abscess, which may rupture. It is suggested that 50% of patients with liver abscesses show a history suggesting previous amebic dysentery.
Conventional treatment consists of amebicides (especially metronidazole) and supportive care, if necessary. Conventional treatment of giardiasis is also metronidazole, or quinacrine. In both cases, reinfection is common.
Optimal treatment is prevention, which may be accomplished by appropriate filtering or cooking of open water, appropriate hygiene in food handling or sexual activity, and care choosing foodstuffs in foreign countries.
differential diagnosis
nondysenteric amebiasis:
irritable bowel syndrome
regional enteritis
diverticulitis
hepatic amebiasis:
pyogenic liver abscess
neoplasm
hydatid cyst
amebic dysentery:
bacillary dysentery
salmonellosis
schistosomiasis
ulcerative colitis
giardiasis:
other intestinal infections
lactose intolerance
intestinal flora imbalance
footnotes