Case #506 - December, 2019
Several employees of a company had complaints of a gastrointestinal illness that presented as diarrhea and abdominal cramping. Employees interviewed by public health workers reported that symptoms started about one week after their attendance at the office holiday party. Some of the food that was available included a mixed fruit salad consisting of berries and melons and a freshly made pesto spread for smoked salmon bites. The employees received medical attention at the company health clinic where stool specimens were collected in a single vial preservative and processed for ova and parasites. The results for all employees were similar; Figures A and B were captured at 400x magnification from a wet mount using light microscopy with differential interference contrast (DIC) and UV fluorescence respectively for the same field. Objects of interest measured 8-10 micrometers in diameter. Figure C was captured at 500x oil magnification from a trichrome stained fecal smear.
What is your diagnosis? Based on what criteria?
The employees had cyclosporiasis caused by Cyclospora cayetanensis. Since more laboratories are using single-vial preservatives, we wanted to demonstrate how C. cayetanensis can be detected. The oocysts are detectable in wet mounts using bright field light microscopy, in this case enhanced using DIC to optimize photographing (Figure A) however, the sensitivity and specificity can be enhanced if UV fluorescence microscopy is used (Figure B). A permanent stained smear is typically prepared from most single-vial preservatives and oocysts can be detected however, they generally will not stain but will present as non-staining, round objects and may exhibit faint refractile contents (arrows in Figure C). As with other coccidia, an acid-fast or safranin stain is the recommend stain (Figure D); C. cayetanensis is variably acid-fast. Diagnostic morphologic feature shown in this case were:
- Round, thick walled oocysts within the size range for C. cayetanensis (8-10 micrometers)
- Auto-fluorescing oocyst walls using UV fluorescence microscopy
More on cyclosporiasis
Images presented in the monthly case studies are from specimens submitted for diagnosis or archiving. On rare occasions, clinical histories given may be partly fictitious.
DPDx is an educational resource designed for health professionals and laboratory scientists. For an overview including prevention, control, and treatment visit www.cdc.gov/parasites/.