Sunday, April 6, 2014

Answer to Case 299

Answer:  Not a human parasite.

This is an incidental finding of a free-living plant/water nematode that likely contaminated the specimen during collection, transport, or staining.  If this had been my case, I probably wouldn't even make mention of the nematode in the actual patient report to avoid unnecessarily raising concerns for the clinician or patient.

If this been a more significant problem (e.g. there had been a lot of these worms present), then I would have taken additional steps such as examining the reagents used in my lab and having a discussion with the clinician about what the patient might have using (e.g. naturopathic douches) that could have introduced the worms into this location.

Many of you wrote in with some good suggestions of what this worm could be, including a variety of human parasites that have similar morphologic features or could conceivably end up in an endocervical location. However, these parasites can be ruled out based on their larger size and lack of expected features (e.g. no narrow anterior end for Trichuris trichiura or no thin pointed tail for a female Enterobius vermicularis. I think that the most challenging worm to rule out was an anisakid (Anisakis sp. or Pseudoterranova decipiens) based on what appeared to be a posterior mucron (see below).  However, this is a look-alike; the structure we are seeing is actually a stylet at the anterior end of the worm, which may be seen in a variety of free-living nematodes. Fortunately size is a helpful differentiating feature; the worm in this case is less than 300 micrometers in length while anisakid larvae are 20 to 35 millimeters in length.

Thank you all for writing in on this case!

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