Case #522 – August, 2020

At a regional diagnostic laboratory, where specimens from the southeastern United States are evaluated, the objects shown in Figures A and B were observed on a wet mount preparation from a fecal formalin-ethyl acetate (FEA) concentrate. The objects measured approximately 160 micrometers in length. What is your diagnosis? Based on what morphologic features?

Figure A

Figure B

The objects shown are artifacts commonly known as “Beaver bodies” (named for the parasitologist Paul C. Beaver). These may be mistaken for helminth eggs such as those of Trichuris trichuria (distinguishable by the much smaller size of 50 – 55 µm and prominent polar plugs) or Enterobius vermicularis (also much smaller at 50—60 µm long and with an asymmetric flattened edge). They may also be mistaken for the coccidian parasite Cystoisopora belli which is considerably smaller at 25 – 30 micrometers. Beaver bodies are actually spores of parasitic algae (Psorospermium haeckelli) that are found in tissues of crayfish and may be detected on O & P examinations of individuals that recently consumed crayfish.