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:
This week's interesting case was donated by Race Rucki and Jason Shearer from the University of Vermont. The patient had recently returned from Belize and found this 'souvenir' in his neck. What is your diagnosis?
Answer to Case of the Week 806: Myiasis-causing fly larva, consistent with Dermatodia hominis
As noted by Idzi, this is an "L3 larva of Dermatobia hominis. Typical are large and heavily pigmented spines that are arranged in neat rows. Also typical for L3 larvae of D. hominis is their general pyriform shape."
Note the lack of spines on the terminal 3 segments, which is characteristic for this species.
Definitive identification is through examination of the posterior spiracles, which are unfortunately a bit hard to see in this case. However, if you use your imagination, (and maybe squint a little bit), you can make out the 3 straight slits with just a slight curve to them, and can appreciate that they lack a peritreme:
Some more wisdom from Idzi:
Fun knowledge fact: Dermatobia hominis flies will not deposit their eggs directly on humans but rather on a bloodfeeding insect, which will transport it to the human host during a blood meal! Therefore this type of myiasis will usually present on "exposed skin areas". In contrast, its African counterpart (Cordylobia anthropophaga) deposits its eggs usually on clothing that is drying outside, thus resulting in myiasis of usually the "unexposed" areas of the body: scalp (putting on a contaminated T-shirt), back, legs (putting on trousers),...
Thanks again to Race Rucki and Jason Shearer from the University of Vermont for donating this classic case!
This week's case was generously donated by Dr. Karra Jones, and features H&E histopathologic sections of intestine from patient with intussusception. Upon close examination, the culprit behind the intussusception can be seen:
Answer to the Parasite Case of the Week 805: Anisakis sp. larva
As noted by Idzi, "For sure the patient has consumed raw/undercooked fish, as this is one of the anisakids! Indeed the Y-shaped lateral chords are typical!" Anisakis species have Y-shaped lateral chords, whereas Pseudoterranova sp. have plumper, 'butterfly' shaped chords.
Here are the characteristic features, including the Y-shaped lateral chords - among the best I've seen:
SM noted that "The location seems to be the intestinal wall or mesentery. The worm penetrated the wall and caused granulomatous inflammation with eosinophils, leading to intussusception."
Thanks again to Dr. Jones for sharing this classic case!
Dear Friends,
On behalf of the Parasite Morphology Hub of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID), I'd like to invite you to participate in a short survey aimed at understanding current practices and diagnostic capabilities in morphological parasitology.
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This week's case is by Florida Fan, and represents a nearly 'picture perfect' representation of a particular filarial species in a peripheral blood smear. What is your identification? For students, residents, and fellows - this is a classic, and definitely fair game on exams!
Answer to the Parasite Case of the Week 804: Brugia sp. microfilaria, favor B. malayi
As noted by Idzi and others, this is a textbook example of Brugia sp. microfilaria, with beautiful terminal and sub-terminal nuclei and a characteristic long cephalic space. However, Idzi rightly recommends caution in committing to a species since B. malayi and B. timori can have a very similar appearance. He notes that "to decide which one, either geographical information is needed (B. timori is more restricted to the Lesser Sunda Islands of the Indonesian archipelago - from Bali over Timor to the Tanimbar Islands - while B. malayi is more widespread in South-East Asia), or information about the stain for the blood film (both Brugia species have a sheath in fact, but if the smear is stained with Giemsa, the sheath of B. timori is usually not visible).
While we don't have an exposure history in this case, the stain is Giemsa, which points us to B. malayi. However, I consider the sheath staining to be a soft diagnostic feature, as I've seen this type of faint pink staining with Wuchereria, and not all B. malayi sheaths stain with Giemsa.
Since the sheath staining is not reliable, we must use the other criteria for differentiating B. malayi and B. timori as follows:
The CDC DPDX also has some nice examples of B. malayi and B. timori.
Thanks again to Florida Fan for donating this beautiful case.
For this week's case, we have a worm submitted from an otherwise asymptomatic teenager. No further history was provided. What is your identification, and how would you sign this case out?
Answer to the Parasite Case of the Week 803: Toxocara species, adult female. Humans are NOT a host for this life cycle stage of the parasite. Therefore, as Philip, Anastasia, Anatoly, HCLM Fan, and others mentioned, the most likely scenario is that this worm came from a family pet instead of the teenager. Less likely, the teenager could have swallowed the worm and its finding in stool represents spurious passage. Unfortunately, we were not able to get any additional history in this case. Hopefully this result was reassuring and helpful to the patient and family.
Although this worm resembles the large human intestinal worm, Ascaris lumbricoides, it can be differentiated in this case by two main features:
First, this worm has pronounced lateral alae, which are not found in Ascaris lumbricoides. (Lateral alae are found in Enterobius vermicularis, but that worm is much smaller and can therefore be excluded).
Apologies everyone for the delay in posting a case. I've been travelling a lot and just returned from South Korea. While I was there, I was offered the following dish consisting of raw crab. If I had chosen to eat it (which I didn't), which parasites could I have acquired?
Answer to the Parasite Case of the Week 802: No significant parasite risk.
But wait, you may say, what about paragonimiasis???
As noted by Anatoly, Kim Tae Yun, and others, these are marine crabs rather than fresh water - an important distinction! Eating undercooked freshwater or estuarine (brackish) crabs could indeed lead to paragonimiasis, and this was historically an endemic infection in Korea. However, the risk from eating undercooked marine crabs is relatively low. According to Kim Tae Yun, "Most Korean people enjoy the food so called GEJANG (crab soaked in soy sauce)...And the GEJANG in the photo looks very delicious."
What do you think?
Anisakiasis and gnathostomiasis are hypothetical risks from eating freshwater crabs as well, but highly unlikely as crabs are not the typical hosts for the associated parasites.
I must admit that I chose not to eat this dish for two reasons: first, I was uncertain about the type of crab offered, and second, I'm not a huge fan of raw seafood. However, the food I did eat, including a crab hotpot and kimchi pancake, were absolutely delicious.
Thank you all for sharing your own experiences.
This week's case was an interesting finding from microscopic examination of skin scrapings. What is your diagnosis? And what forms are you seeing?
