This week's case was generously donated by Dr. Jacob Rattin, a pathology resident at Cleveland Clinic.
A traveler returning from a lengthy hiking exploration in South America presented with itching, pain, and lesions on the soles of their feet. A skin biopsy was performed with showed the following on hematoxylin and eosin (H&E):
H&E, 25x magnification
Answer to the Parasite Case of the Week 815: Tungiasis, caused by the flea Tunga penetrans
The following excellent description is written by Dr. Rattin:
Tungiasis is endemic in Latin America, sub-Saharan Africa, and the Caribbean. As is sadly all too common, it predominantly affects resource-poor communities. There is no standard treatment, but recommendations include surgical removal, wound disinfection, and dimeticone-based topical therapy (NYDA – a mixture of two low-viscosity dimeticones).
Tunga penetrans is the chigoe flea (with myriad other names). Gravid females lay eggs which are shed in the environment. Here, the eggs hatch into larvae, which have two stages prior to forming pupae. The pupae are in cocoons, from which the adults hatch and search for a warm-blooded host. The males and females can feed on the host, but only the females will burrow into the skin. This answers the question in the case whether this is a male or female – it is a female since it has burrowed and because of the numerous eggs that are visible. Only the posterior ends will be exposed to the environment, with their anterior end burrowed into epidermis. They can shed about 100 large eggs over a two-week period. They will then die and be sloughed off by the host’s skin. The damage to the skin can cause secondary bacterial infections, even possibly leading to sepsis. If the patient tries to remove the embedded female by themselves without sterile tools, tetanus is also a possible complication.
The hematoxylin and eosin (H&E) stained sections showed hyperkeratosis of the overlying host skin and important features diagnostic of tungiasis. Identifiable features are the sclerotized cuticle (yellow) and tracheal rings (Figure 1), digestive tract (Figure 2), and numerous large eggs (Figure 3). The eggs are actually visible to the naked eye! These features, along with the large size of the embedded flea and the position within the epidermis help differentiate Tunga penetrans from other arthropods such as scabies and ticks that may be seen embedded within skin.
Figure 1, H&E, 100x magnification:
Figure 3, H&E, arrows pointing to two of many eggs. 100x magnification
Thanks again to Dr. Rattin for donating this great case!
It's the first Monday of the month, and time for another great case by Idzi Potters and the Institute of Tropical Medicine, Antwerp, Belgium!
The following object was found in a soil sample from a child's playground. It is approximately 80 micrometers in largest dimension.
Answer to the Parasite Case of the Week 814: Toxocara sp. egg, most likely T. canis based on size.
As noted by several readers, Toxocara eggs are spherical to subspherical, and have a thick, coarsely-pitted shell. HLCM Fan shared the following story: "I remember a professor in college telling us the eggs of Toxocara look like golf balls, but nobody there ever saw one (a sport for only the privileged here), so when I teach, I say the look like styrofoam balls (a big ball made of tiny balls)."
Note the characteristic pits in the shell of this embryonated Toxocara egg:
The video is particularly effective in showing the outer surface.
According to the CDC, T. canis is presumed to be the most common species to infect humans. This is likely due to several factors: transplacental transmission ensures that many puppies are infected from birth; dogs, especially puppies, shed enormous numbers of eggs; and dogs often contaminate areas where children play. However, recent molecular studies have shown that T. cati is probably an underrecognized cause of human infection.
Eggs of Baylisascaris procyonis, the raccoon round worm, may also be found in soil and have a similar appearance to those of Toxocara, but have a finely mammillated or granular outer surface. Their size range is slightly smaller than that of Toxocara eggs, but there is significant overlap.
Finding Toxocara (and Baylisascaris) eggs in a child's sandbox is a significant finding, as both can cause visceral larva migrans VLM if the eggs are ingested by a human host. Following ingestion, the eggs hatch to release a larva that migrates throughout tissues, including the liver and lungs. Clinical manifestations range from asymptomatic infection to severe disease, with symptoms depending on the number of larvae, the organs involved, and the host's immune response.
Given the potential significance of VLM, it is important to prevent environmental contamination by keeping sandboxes covered when not in use, to prevent them from being used as latrines by infected dogs, cats, and racoons (!) In this case, there is no practical way to reliably decontaminate the contaminated sandbox, since the eggs are extremely resistant to environmental conditions and can remain infective in soil or sand for months to years after embryonation. It's best to completely remove or replace all of the sand.
Thanks again to Idzi Potters and ITM for donating this great case!
This week's case was donated by Heather Morris, the parasitology lead in my laboratory. We received the following objects for identification:
This week's case features two ~1 cm long tan-white worms removed from the terminal ileum during routine colonoscopy. What is your identification?
Anterior end:
Posterior end - worm one:
Answer to the Parasite Case of the Week 812: Adult hookworms, male and female.
As noted by Idzi Potters and Florida Fan, it's a bit hard to make out the mouth parts from the first photo. However, by focusing up and down on the actual clinical specimen, we were able to confirm that there are 2 pairs of teeth present, consistent with Ancylostoma duodenale. The second image shows the end of the female worm, whereas Idzi notes that the third "gives a nice view of the bursa copulatrix - a specialized organ found in male hookworms, used for sensing and grasping during copulation." The spicules at the end of the male do not appear to be fused, which supports the identification of A. duodenale.
Florida Fan noted that "The images may be sufficient for treatment but for academic purposes they pose a challenge. Would a stool parasitology culture help to identify the species involved?" This is a great question. If eggs are present in the stool, they could be hatched using the Harada Mori or similar culture method, and this would allow them to develop into L1 and eventually L3 larvae. There are some subtle differences between the L3 larvae of the different hookworm species, so it might be possible to differentiate them from the L3 stage alone. However, I'm not sure I would be able to accurately differentiate them. Unfortunately, this is where the life cycle stops for stool culture; we can't rear the larvae into adults, since this requires entry into a suitable host. Thank you for bringing up this option, Florida Fan!
This week's case was donated by Dr. Francesca (Frankie) Lee. The following images are from Gram-stained and wet prep slides of a BAL from an immunocompromised patient.
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:
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!
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!
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.
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.
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!
This week's case is a worm that was reportedly vomited from a teenager and found in the toilet. What is your identification?
Answer to the Parasite Case of the Week 808: Nematomorph (a.k.a. gordian or horse hair worm), or similar appearing worm. As noted by an anonymous reader, this is "most likely nematomorpha but would need to examine under magnification. I have encountered many museum specimens labeled as horsehair worms that were in fact mermithid nematodes or haplotaxid annelids."
Regardless of the definitive identification, the important thing to mention in the report is that this worm is NOT a human parasite. It was most likely found in the toilet and not actually vomited by the patient.
As discussed by Idzi, "The adults of the Nematomorphs are not parasitic (they live in water) but the larvae are parasitic and use terrestrial insects as their host. Once the larva inside the insect has matured (after several molts), the infested insect will have an irresistible urge to drown itself, thus bringing the adult worm back to water. Neat trick!" This is one of several parasites that manipulates the host to further its own life cycle - another being Toxoplasma gondii in the rodent host.
I've featured this parasite a few other times on this blog, and have written a longer description that you can read HERE. This link will also bring you to other cases, including one with a very graphic video of a worm emerging from a cricket 😯. As described by Florida Fan, "What else can I say. The “equine chevelure” though not so “knotted" is very vivid?
Happy Lab Week! In honor of this special week, I wanted to share these images from our long-time contributor, Florida Fan. He made these kites himself. Can you guess what parasite is represented?
Answer to the Parasite Case of the Week 807: A beautiful Giardia kite by Florida Fan
We had a lot of great comments on this case. Many viewers commented on how 'cute' the kite was, and so easily recognizable. Some wanted to buy the kite for themselves - Florida Fan, you could consider starting a business!
Here are few other comments that made me laugh:
