Answer to Case 757

 Answer to Parasite Case of the Week 757: Hookworm rhabditiform (L1) larvae

Many of you questioned if these were Strongyloides stercoralis larvae, since this parasite most often presents with L1 larvae in stool. In comparison, hookworm larvae are rarely seen in stool, and only when there is a prolonged period between specimen collection and placement in fixative (as occurred in this case). Fortunately, hookworm L1 larvae can be differentiated from those of S. stercoralis L1 larvae by several morphologic features:

• Hookworm larvae (Ancylostoma duodenale and Necator americanus) have a long buccal cavity and an inconspicuous genital primordium.
• S. stercoralis larvae have a short buccal cavity and conspicuous genital primordium. (Think Strongyloides = Short)

Note the long buccal cavity in this case:

Here is a nice image from Case of the Week 459 showing the two L1 larvae side-by-side:

While I tried to provide you some clues to the diagnosis (received fresh, not in preservative, and larvae were no longer motile upon examination), this was definitely a challenging case!

Thanks to everyone who wrote in with their thoughts.