Answer to Case 526

Answer: Enterobius vermicularis

As noted by Florida Fan, the diagnostic features shown in this case include the cephalic alae, esophageal bulb, and "D-shaped" eggs (oval with a flattened side). Natalie Ellis described them as 'coffee bean' or 'paper weight' shaped - I had never heard those analogies before!

Thanks to Bernardino Rocha and Silvia for the interesting comments about the different Oxyuroidea found in mammals, reptiles and amphibians (see the comments section on this post for the full details). Thank you also to Old One who reminded us that dogs and cats do not have pinworm and are not the source of your child's infection! I'm amazed that this connection would be made, given how ubiquitous pinworms are. Infection could almost be considered a right of passage in childhood.

Infection is usually diagnosed based on the clinical symptoms (nocturnal pruritus ani) and identification of eggs +/- adult females on the cellulose tape test. Just yesterday I had the privilege of visiting the Meguro Parasitological Museum in Tokyo and got to see their large array of fascinating specimens. Here are a couple of images from their museum:

Japanese 'tape prep' kit:

Statistics showing a significant decline in pinworm infections in Japan - likely due to the required annual tape prep exams that are obtained for all school-aged children (see an interesting blog post from a mom on this topic HERE):

And finally, a lovely poem by Blaine:
Dwelling deep down in the lumen of your large intestine
a female pinworm is making her way to the perianal skin
for before the rooster crows
she'll lay eggs in droves
that are going to cause your booty to start itchin'