Answer to the Parasite Case of the Week 787: Adult Ascaris sp.
As Florida Fan and Idzi noted, the curved posterior end suggests that this is a male adult.
Ascaris is the largest nematode to reside in the human intestinal tract. Adults live in the small bowel and must move against peristalsis to avoid being expelled in the stool. The fact that they are freely moving and not attached to the intestinal wall means that they can occasionally end up in ectopic locations such as the biliary tree or appendix. In this case, the worm migrated up the intestine, stomach, and esophagus, and was expelled through the mouth (!) Given its large size, heavy infections can lead to the potential deadly complication of small bowel obstruction.
Some readers made the interesting point that this could be either Ascaris lumbricoides or the zoonotic Ascaris suum, which raises the controversial topic of Ascaris taxonomy!.Although they were long thought to be separate species, Ascaris suum was found to be genetically similar to the human species A. lumbricoides in a 2014 comparative analysis of microRNA profiles, arguing against separation into Ascaris two species. However, a 2020 analysis using whole genome sequencing found significant genetic differentiation between A. lumbricoides and A. suum populations. Therefore, it looks like the two populations are genetically distinct and likely deserve separate classifications. We can hopefully look to future analyses to more fully understand their taxonomic status.
Thanks again to Dr. Beth Adams who donated this case, and to Drs. Mike Adams and Bill Stauffer who shared the image and video with me initially.
3 comments:
Although this is straightforward case as the worm was expelled from the nose, often in the developed world, people think they have passed a worm in the toilet bowl. More often than not, earthworms find their way into a toilet bowl due to a leak in plumbing. These can be the size of Ascaris but have distinct morphological features - segmented body and clitellum. I have been told ( by my ‘fishermen’ friends who use these as baits for fishing as they wriggle in water!) that some earthworms like water and find their way into water systems. So beware and have a good look before reporting.
No, there definitely aren’t earthworms in the toilet! That’s the first I’ve heard of it and a hilarious explanation as I wonder how they get into high rise condos. Parasites are much more common in the developed world. Tapeworms in Alberta known to be growing into metropolitan problem as coyotes spread it to domesticated animals and humans. Lack of evidence isn’t evidence; we don’t have the testing to facilitate proper diagnosis.
As crazy as it may sound, earthworms can definitely enter cracked or broken pipes in the ground and swim up into the toilet. As Dr. Sheorey mentioned, they are fast and strong swimmers! We get them occasionally in our laboratory for identification after being retrieved from a patient's toilet, and careful examination allows us to unequivocally identify them as earthworms (which have several distinct features including a band-like clitellum). Having said that, there is probably a limit as to how high up they would usually swim, so they probably don't get into high rise condos ;)
Regardless, the fact that the worm was actually removed from the patient in this case and the overall appearance is strongly supportive of this being an Ascaris worm.
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