Answer to Case 567

Answer: Hymenolepis nana egg.
As many of you pointed out, this eggs beautifully demonstrates the filaments arising from the 2 poles of the inner membrane (arrow heads, below image). You can't make it out here, but there are 4-8 of these filaments arising from each pole. You can also nicely see the hooks of the 6-hooked oncosphere:

Some of you may know that humans become infected with this parasite when they ingest infected arthropods. As Sam mentioned, children are a common host - likely due to their tendency to put things in their mouth. Adults can also become infected as Blaine reminds us in his poem:

There once was a chap from Indiana

who with his cereal enjoyed a banana

but with the cereal he did eat

he received an unexpected treat

The cestode known as Hymenolepis nana!

If you do an internet search for "oatmeal" and "bugs," you will find multiple consumer complaints (and some nice YouTube videos) to explain the cereal reference.

Importantly, infection via ingestion of eggs shed in stool (autoinfection or from another person) is also possible, making this a common intestinal cestode infection worldwide.