Case #521 – August, 2020

As part of a refugee screening program, a young child had a fecal ova and parasite (O & P) examination which included a formalin-ethyl acetate (FEA) fecal concentration. Objects shown in Figures A–C were detected in low numbers on a wet mount preparation and measured about 75 micrometers on average. What is your diagnosis? Based on what morphologic features?

Figure A

Figure B

Figure C

This was a case of hymenolepiasis caused by Hymenolepis diminuta. Diagnostic morphologic features shown in the images included:

eggs within the size range for H. diminuta.
presence of an inner oncosphere without polar filaments in the space between the oncosphere and the outer shell/membrane (which would be present in the smaller eggs of H. nana).
presence of hooks in the oncosphere (best seen in Figures B and C).
an outer membrane/shell with striations.