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!
