Answer to Case 811

Answer to the Parasite Case of the Week 811: Strongyloides stercoralis L3 larvae; presentation consistent with hyperinfection. 

As noted by Florida Fan, this is a "typical case of full blown invasive strongyloidiasis. The Gram stain didn’t give us much detail for the identification. The wet mounts appear to show the notched tail of the infective filariform stage."

Here is a closer up view of the notched tail from Dr. Lee, confirming the identification of S. stercoralis L3 larvae:

(The notch is very subtle and can be difficult to appreciate) 

Florida Fan also shared that while the "filariform larvae cannot penetrate nitrile examination gloves, I would surely take extra precautions while handling such a specimen such as double gloves." HLCM Fan also shared a story of a past case: " We had a case of S. stercoralis a years back and went a little crazy with lab security measures (double gloves, nobody could use the BSC after us before we clean it with alcohol and UV, biosafety apron with sleeves, the samples were inactivated before leaving the lab, etc). We were not exaggerating; this sample is really dangerous."

These precautions are important as L3 larvae can penetrate intact skin and cause infection in the human host. In addition to glove use, we would tape up the bacteriology culture plates to prevent the larvae from migrating outwards.

HLCM Fan asked how we can differentiate the larvae in this case from those of S. fuelleborni. Fortunately, the answer is simple: S. fuelleborni does not have an autoinfection cycle, so we would not expect to find L3 larvae in a respiratory specimen during the chronic stage of infection. It is only during the early acute stage that the larvae may migrate through the lungs before reaching the intestinal tract (see the CDC lifecycle).  

Thanks again to Dr. Frankie Lee for donating this classic case!

Case of the Week 810

This week's case features some immature insects submitted in a sterile collection cup with balled up tissues inside. The patient is a middle-aged female, and no source or clinical information is provided 🫤. 

Looking closely, 3 tiny brown specs ~ 1mm in size could be seen through the cup using the dissecting microscope. Our lab staff are rightly cautious about opening containers when tissue or other material obscures the contents in case there is something alive and/or contagious inside!

After seeing no movement for a few seconds, they opened the container and retrieved the following 3 objects:

What is your identification?

Answer to Case 810

Answer to the Parasite Case of the Week 810: Pediculus humanus (head and body louse) nymphs

As noted by Richard Pollack, these are Pediculus nymphs. As he succinctly put it, "If from the scalp, they're head lice. If from the body or clothing, body lice."

Unfortunately, as is often the case, we did not receive any clinical history. There were also no clues from the specimen itself—such as attached nits on hair shafts—or information regarding the collection site that would allow us to distinguish between head lice (Pediculus humanus capitis) and body lice (Pediculus humanus humanus).

Several readers commented on the prominent eyes of the immature lice. This is a feature commonly seen in juvenile animals, where the eyes appear disproportionately large relative to the rest of the body. These early-stage lice (nymphs) are no exception. In fact, their oversized eyes and compact bodies give them a surprisingly "cute" appearance—at least from my perspective, recognizing that not everyone shares the same enthusiasm for parasites!

Of course, these youngsters are already equipped with the claws and mouthparts needed to begin life as obligate human ectoparasites. Cute is definitely in the eye of the beholder.

Case of the Week 809

This week's case is a little tricky. We received the following fly larva from a patient living in the upper midwestern United States. No additional information was provided. Based on the images, how would you sign this case out? Would you request any additional information?

 

 

Answer to Case 809

Answer to the Parasite Case of the Week 809: Fly larva, most likely a member of the family Calliphoridae. As noted by Idzi Potters, "This is an L2 larva, as there are only two slits. This makes ID very challenging. The cute hand-with-too-many-fingers-like anterior spiracles make me believe that this is a larva from the family Calliphoridae (Calliphora sp. or Lucilia sp.), causing facultative myiasis." Here is the image of the anterior spiracles (hand with too many fingers) that Idzi is referring to:

Unfortunately, this is as far as we can comfortably go with our identification in this case. It is especially important to note is that most taxonomic keys such as the CDC Pictorial Keys or the manuscript that Blaine Mathison and I wrote for Clinical Microbiology Reviews are for third instar larvae and cannot be reliably used for most of the second instar larvae. If you had used these keys in this case, you may have ended up with an aberrant identification such as Cochliomyia. This genus includes C. hominivorax, the New World screwworm, and finding it could have important epidemiologic and clinical implications since it causes destructive infestations and has been eliminated from the United States.

To better understand the significance of this case, we called the outside provider and discovered that the larva was found in the toilet of an asymptomatic woman from the midwestern United States with no travel history. It was therefore considered a case of environmental contamination and not true myiasis. 

Parasitology Workshop at ASM Microbe!

Dear Readers, if you are going to ASM MICROBE in Washington, DC this June, come a day early and enroll in an amazing, full-day, Parasitology Workshop with Blaine Mathison, Idzi Potters, Marc Couturier, and Anisha Misra. They will be covering diagnostic approaches to parasitic infections, pitfalls and mimics of infections, and essential topics for daily clinical use. I hope to see you there!

https://invt.io/1lxb8enijcv