Answer to Parasite Case of the Week 615: Strongyloides stercoralis rhabditiform larva, eggs, and adults. Note the eggs inside and out of the beautifully-photographed adult worms by William Sears. As you may know, the parasitic females reproduce without the males using a process called parthenogenesis.
This 'composite' case didn't have any accompanying clinical information, but a classic scenario would be hyperinfection infection in a profoundly-immunocompromised patient.
It's important to note that it's not possible to definitely make the diagnosis on the images from this case alone, especially since the buccal cavity of the rhabditiform larva is not visible. You all did an excellent job coming up with the differential diagnosis. I'd highly recommend reading all of the comments on the blog (or on Twitter @Parasitegal) to see great descriptions and stories.
Here are the options of what this case could be:
1. S. stercoralis hyperinfection (For another example, see the previous Case of the Week 469 and the accompanying Answer). It's important to realize that embryonated eggs and adults may rarely be seen in stool specimens in heavy infections. Here's a great photo from Case 469 to demonstrate the size difference between adults and rhabditiform larvae:
2. Strongyloides fuelleborni infection, in which eggs containing rhabditiform larvae are found in stool. In this case, we wouldn't have expected to see adult worms in the stool. See the previous Case of the Week 593 donated by Idzi Potters for more information.
3. Hookworm infection, in which unfixed stool was allowed to sit for some time prior to examination, allowing eggs to embryonate and hatch. Great thought! This doesn't account for the adults in stool, however, which would not be expected in hookworm infection.
4. Mixed hookworm and Strongyloides infection. Allowing the eggs to hatch (e.g., using the Harada-Mori culture technique) and then examining the rhabditiform larvae would allow for differentiation of hookworm and Strongyloides. Alternatively, molecular testing at a specialized research laboratory could also help to sort this out.
5. Spurious passage of a soil/plant nematode.
Wishing you all a very happy and safe Thanksgiving day!