Prevalence ofDientamoeba fragilis antibodies in children and recognition of a 39 kDa immunodominant protein antigen of the organism

Abstract

Dientamoeba fragilis, a common intestinal protozoan parasite in Canada, has been associated with diarrhoea and abdominal pain in some patients. Seroprevalence of this organism has not been reported previously. In the present study sera from three symptomatic patients, 12 age- and sexmatched controls, and 189 randomly selected healthy individuals (age 6 months to 19 years) were tested for antibodies againstDientamoeba fragilis by an indirect immunofluorescence (IIF) assay. All three symptomatic patients infected withDientamoeba fragilis had positive IIF titres of 80, and all 12 matched controls had positive titres ranging 20 to 160 (geometric mean titre 48). Of the 189 healthy children, 172 (91%) were positive at a serum dilution of 1∶10 or higher. The specificity of the IIF assay was reinforced by immunoblotting 20 representative serum samples againstDientamoeba fragilis, In all 17 IIF-positive serum samples, a 39 kDa protein band ofDientamoeba fragilis was identified, the same band recognized by a mouse monoclonal antibody raised in our laboratory. Findings over a five-year period indicate thatDientamoeba fragilis was the most common protozoan, followed closely byGiardia lamblia and more distantly byCryptosporidium parvum. The high seropositivity of 91% forDientamoeba fragilis compares reasonably well with serologic data obtained by IIF and reported previously forGiardia lamblia (85.6%) andCryptosporidium parvum (86%).