Vignette 59: This 55 year old Montreal male went for his first routine preventive colonoscopy. He had normal daily stools that appeared normal. He had not traveled to the tropics except for 2 years wandering around Asia (1980-1982) and a trip to Jamaica 15 years ago. The gastroenterologist biopsied the "cecal ulcerations and erythema" seen here. The rest of the colon appeared normal. The H&E histology revealed a necrotic mucosa with hematophagous amoebic trophozoites. If this is amoebic colitis is it possible he has had asymptomatic cecitis for 18 years? The answer is.

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Vignette 59: An E. histolytica PCR on the fixed biopsy tissue was positive and an E. dispar PCR was negative (Public Health Laboratory, Quebec). There are anecdotal reports of prolonged (up to 32 years) intervals between tropical exposure and amoebic liver abscesses but these are anecdotes.(1) Clinical studies indicate that 95% of amoebic abscesses occur within 5 months of returning from the tropics, and that asymptomatic E. histolytica infection has a mean half-life of over 15 months.(2)  The possibility of E. histolytica sexual transmission makes it almost impossible to determine the incubation period in this case. We don't see E. histolytica infections in non-traveling Quebecers.

1) Knobloch J et al. Development and persistance of antibodies to Entamoeba histolytica in patients with amoebic liver abscess. Analysis of 216 cases. Am J Trop Med Hyg 32: 727-32: 1983.

2) Blessmann J et al. Longitudinal study of intestinal Entamoeba histolytica infections in asymptomatic adult carriers J Clin Micro 41: 4745-50: 2003