Monday, October 3, 2022

Case of the Week 697

 It's time for our monthly case from Idzi Potters and the Institute of Tropical Medicine, Antwerp!

The following structure was seen in a lugol-stained wet preparation of concentrated feces.  

The corresponding iron hematoxylin stained fecal smear showed the following:


Monday, September 26, 2022

Case of the Week 696

 The following objects were seen in a urine specimen from a young man originally from sub-Saharan Africa. What are we seeing here? The beautiful photos are by Felicity Norrie, MLS(ASCP).

Sunday, September 25, 2022

Answer to Case 696

 Answer to the Parasite Case of the Week 696Schistosoma haematobium egg and larva (miracidium).

As noted by Florida Fan, the morphology of the eggs is consistent with S. haematobium and S. intercalatum, as both are ovoid with a terminal spine. However, S. haematobium is usually found in urine, whereas S. intercalatum is usually found in stool. I didn't provide a size in this case, but it's helpful to know that S. intercalatum is also usually longer than S. haematobium and has a central bulge.

It is unusual to see a free miracidium in the urine. Note the circumferential cilia which gives it a shaggy appearance. 

TheOracle and Idzi mentioned that the presence of the free miracidium suggests a delay between sample collection and microscopic evaluation without preservation. Hatching of Schistosoma eggs can also be triggered by dilution of the specimen in water. Idzi had previously donated a beautiful case of a motile miracidium to this blog, which you can see HERE. Look how fast it is! This miracidium was also initially moving, but had stopped by the time we attempted to take a video. Thanks again to Felicity Norrie for these beautiful photographs!

Tuesday, September 20, 2022

Case of the Week 695

This week's case is a very sad situation in which a highly immunocompromised patient died from her parasitic infection (in addition to multiple other co-infections). The following is a whole slide scanned section from her small intestine that was obtained at autopsy. 


Here are some screen shots as well:

What is your identification? 

Bonus questions:

  1. Are there any infectious concerns with with handling the fresh autopsy specimens?
  2. What parasite forms are seen in this specimen?

Sunday, September 18, 2022

Answer to Case 695

The following excellent answer to this week's case is by our guest author, Jacob Rattin (@eternalstudying), medical student and future pathologist. 

Answer to the Parasite Case of the Week 695: Strongyloides stercoralis hyperinfection. 

Many readers commented that this was Strongyloides stercoralis, with several Twitter and LinkedIn users correctly mentioning “hyperinfection.” Great job! Here is the DIGITAL SLIDE for your reference. 

While this case had a very sad outcome, it highlights important features of Strongyloides hyperinfection. Individuals who are elderly or immunocompromised (eg, solid organ transplant, malignancy, corticosteroid treatment) are more likely to experience hyperinfection and severe disease. Hyperinfection can be life-threatening, as it was in this case, with massive numbers of larvae invading the tissues and resulting in death. 

In this histologic section, the eggs and larvae are easily appreciated. These forms are part of the infective life cycle, which starts when a human is infected by filariform larvae penetrating the skin, entering dermal vessels, and journeying to the lungs. The larvae then migrate up the bronchial tree, are swallowed, and arrive to the intestinal tract. Here, they mature into the adult female worms and begin laying eggs. An autoinfective cycle is part of the normal life cycle, and allows for perpetuation of the infection for decades. In the intestinal tract, female Strongyloides stercoralis worms are parthenogenic and do not need a male worm to make or lay eggs (“Who needs men?!” – Quote from Strongyloides stercoralis females, probably). With immune compromise, the low level of autoinfection can turn into a dangerous level of hyperinfection, leading to intestinal and pulmonary hemorrhage (from migrating larvae), bacteremia and bacterial meningitis (from gut flora carried by the larvae), and extensive organ damage. We can appreciate the damage to in the intestinal tract in this case, with extensive denudation and sloughing of the epithelial cells. 

You may recall from previous blog posts that eggs usually do not appear in the stool since they hatch and release rhabditiform larvae in the intestine. This case shows intestinal eggs with appreciable maturation within the eggs. Larvae within blood vessels (on their way to other organs) can also be seen. The histopathologic appearance in this case is diagnostic for strongyloidiasis. The only other infection that has a similar appearance is intestinal capillariasis, but the eggs have a very different appearance. 

Bonus Question Answers:

1.  Are there any infectious concerns with handling the fresh autopsy specimens?

Yes! With Strongyloides stercoralis, it is possible for those handling the autopsy to be infected with the filariform larvae that penetrate human epidermis. As Florida Fan said, “As always when dealing with Strongyloides stercoralis, all precautions should be taken to avoid a percutaneous infection with filariform larvae possibly present in the raw specimen.”

2.  What parasite forms are seen in this image?

As mentioned above, the parasitic forms observed are egg, larvae (rhabditiform, and filariform), and even the rare adult female.

Monday, September 12, 2022

Case of the Week 694

Hello Readers! I'm back after some busy weeks and an overseas holiday, and am pleased to announce that I have a guest author for this and next week's post, Mr. Jacob Rattin. Our case for this week was donated by Dr. Susan Butler-Wu, Dr. Ria Vergara, and Lowel Ordono. They noticed this intriguing findings in a wet preparation of BAL specimen from an immunocompromised patient and worsening respiratory status. The specimen had been stored refrigerate for >24 hours. Identification?

Sunday, September 11, 2022

Answer to Case 694

The following excellent answer to this week's case is by our guest author, Jacob Rattin (@eternalstudying), medical student and future pathologist. Hopefully we will be able to recruit him to my residency program at Mayo Clinic!

Answer to Parasite Case of the Week694: BAL showing a ciliated respiratory epithelial cell exhibiting ciliary movement.

If you reach back into your memories from undergrad cell bio, motile cilia contain “9+2” axonemes made up of 9 doublet microtubules and a central pair of microtubule singlets. The peripherally located “9+2” doublets are associated with several accessory proteins, with dynein arms being most relevant to us in this case. The dynein arms provide ATP-dependent motor function, with hydrolysis of ATP resulting in sliding of the axoneme and ciliary movement, which is what you are seeing in the video. The respiratory epithelial cell does not have to be a part of the tissue to exhibit their back-and-forth motion. If ATP is available for hydrolysis, the dynein arms will provide ciliary movement!

As a reminder, ciliated epithelium can be found in the following regions:

• Upper respiratory tract

• Fallopian tube and parts of the endometrium 

• Ependymal cells that line the ventricles in the brain 

• Caput epididymis/efferent ducts

• Locations in which ciliary metaplasia has occurred

Some folks on Twitter, LinkedIn, and in the comments section of this blog were thinking Lophomonas blattarum, a multiflagellate protozoan that occupies the gut of the cockroach Blatta orientalis. While there are similarities between the two regarding their morphology, there is no good evidence at this point that L. blattarum is a human pathogen, nor that it is found in BAL. What is often misdiagnosed or misidentified as L. blattarum is actually a ciliated respiratory epithelium in various stages of degeneration. Furthermore, molecular studies have questionable validity due to the non-specific PCR primers that have been used. In the comments, Richard Bradbury went into fantastic detail stating, “I reviewed the PCR primers used in these papers. The forward and reverse PCR primers in a standard “all-sequences on Genbank” BLAST showed the first series of hits to flagellates of various forms (L. blattarum and a lot of different trichomonads), all at 100% identity for both primers. This does raise the possibility that the positives they identified were actually Trichomonas tenax, which is normal oropharyngeal flora, or another unidentified commensal trichomonad of the oral cavity.

So, what’s next? We suggest sequencing of L. blattarum taken from the gut of the cockroach B. orientalis to compare to the ciliated respiratory epithelium (or, the purported L. blattarum) taken from a BAL. This would bypass the morphologic ambiguity that surrounds this issue and give us a more definitive answer. 

Monday, August 22, 2022

Case of the Week 693

 This week's case was kindly donated by Dr. Mike Mitchell and his laboratory. The patient is a middle-aged man with fever, intermittent cough, headache and mental status changes. He had a history of lymphoma and was receiving maintenance immunosuppressive chemotherapy. Of note, he had several episodes of bacteriemia and progressively worsening pulmonary infiltrates. He was originally from Sub-Saharan Africa but had been living in the United States for several decades. 

The following are images from a duodenal aspirate:

What is your diagnosis?

Sunday, August 21, 2022

Answer to Case 693

Answer to Parasite Case of the Week 693: Strongyloides stercoralis larvae

As many of you mentioned, the large number of larvae is very concerning for strongyloides hyperinfection, so an urgent call to the treating physician is indicated. 

The single larva seen here is an rhabditiform (L1) larva. It has a short buccal canal (shown) and prominent genital primordium.

Wednesday, August 17, 2022

Case of the Week 692

 This week's case is a bit different in that it wasn't actually alive. Instead, it is a stunning glass artwork of an object that is important in the world of human clinical parasitology. What am I showing here?

This amazing work is by Jane Hartman (@trilobiteglass). You can find her Etsy shop HERE! (Posted with permission)

Sunday, August 14, 2022

Answer to Case 692

Answer to the Parasite Case of the Week 692: Female copepod with a Dracunculus medinensis larva inside. This stunning glass art was made by Jane Hartman (@trilobiteglass) and gifted to me by my friend and colleague, Dr. Audrey Schuetz (@schuetz_audrey). 

Here are some of the key features:

This case is particularly special since it was the topic of the very first unknown case I ever posted on this blog - way back in 2007! You can see it here: Parasite Case of the Week 1.

Thanks to everyone who has stuck with me along the way - 7 years and 691 posts later! - and to those of you who have joined along the way.

Monday, August 8, 2022

Case of the Week 691

This week's case was generously donated by Dr. Nicole Brammer Hubbard. Several of the following objects were removed from ear of a child after the parents noticed a bloody discharge (!)  Identification?

Sunday, August 7, 2022

Answer to Case 691

 Answer to Parasite Case of the Week 691: Fly larva, consistent with Lucilia species, (or as Florida Fan noted, "I love Lucy!") 

There are numerous keys for identifying fly larvae, including the freely-available CDC pictorial keys ( and a simplified key that Blaine and I published in our review on Laboratory Identification of Arthropod Ectoparasites (Clinical Microbiology Reviews). These keys are very easy to use once one is familiar with the basic morphologic parts of fly larvae (e.g., spiracular plates, mandible). 

Identification to the species level is based on several features including the general body characteristics, arrangement of cuticular spines, mouthparts, and the posterior spiracles. In this case, Dr. Brammer Hubbard was able to get beautiful photographs of all of the key morphologic features so that we can easily make our identification. These show us that there is not an accessory oral sclerite on the mandible, the posterior spiracular slits are straight, and the spiracular plate and button are not heavily sclerotized. This leads us to a final identification of Lucilia species. 

Lucilia is a cause of facultative wound myiasis rather than obligatory myiasis. If you are interested, you can read about it in the chapter that Blaine and I wrote on "Encyclopedia of Infection and Immunity: Parasites of the Ear." (Let me know if you'd like a copy 😊)


Monday, August 1, 2022

Case of the Week 690

This week's case is in honor of @JMGardner who showed a beautiful example of this finding a little while ago. This one is not quite as good, but still diagnostic. The digital slide can be viewed HERE. This is a low power view:

What information can be gleaned from this biopsy, and what would have been the preferred method for identification?

Sunday, July 31, 2022

Answer to Case 690

 Answer: Embedded hard tick, partially engorged with blood. 

As noted by Florida Fan, it is unfortunate that this tick was sectioned for histopathology, since "we need to examine the anal groove, the shield, the palpi, and the basis capitulum" in order to identify the tick to the genus and species level. This level of identification is helpful for patient management, since different species serve as vectors for different microorganisms. Additionally, finding an engorged Ixodes scapularis in a region of high Lyme disease endemicity may prompt antibiotic prophylaxis in certain situations. 

Without being able to examine the external features , we can only make some general comments about the tick in this case. As noted by Richard Bradbury, the tick is engorged, it has a scutum (dorsal shield), and the scutum takes up <1/3 of the body. Thus, we can state that this is a female hard tick. There is also an apparent lack of festoons (although this is hard to assess in sagittal section), and thus the tick may be an Ixodes species. Here are some of the key diagnostic features:

One may ask "why remove the tick like this at all?" Would it have been easier (and much less invasive) to simply remove the tick with tweezers? While I don't know why the tick was removed by excision in this case, I'm guessing that it was misidentified as a thrombosed skin tag. 

Thank you all for writing in with the excellent comments!

Monday, July 18, 2022

Case of the Week 689

 This week's case is from a middle-aged woman with unexplained small bowel perforation. Here is the section with the culprit. You can view the whole slide image HERE. What is your diagnosis?

Sunday, July 17, 2022

Answer to Case 689

 Answer to the Parasite Case of the Week 689:  Anisakid, most consistent with an Anisakis species.

Hopefully you all had a change to look at the whole slide image HERE. From its location in the small intestine, deep in the submucosa, one can envision how it may have extended through the wall of the intestine and caused a perforation. 

Dr. Luca Fanasca noted that "we can clearly see features consistent with an anisakid infection: multilayered cuticle (from a portion which seems detached, in the upper part), polymyarian muscle cells, the beautiful Y shaped lateral chords and the banana-shaped excretory cell. From the quite slender appearance of the lateral cords I think we could suppose this is actually an Anisakis sp., but a definitive identification would require the observation of other characteristics like the caecum position and shape, or molecular diagnostics strategies." 

Below are some of the key features of nematodes, and anisakids in particular: 

Features of all nematodes:

  1. Acellular outer cuticle (may be adorned projections in some nematodes (e.g., the lateral alae of Enterobius vermicularis, and the cuticular bosses of Loa loa)
  2. Underlying musculature. The musculature is either flattened (platymyarian) or tall (coelomyarian). The musculature is further categorized by the number of muscle cells: meromyairan (2 to 5 rows) or polymyarian (large number of rows in each sector)
  3. Lateral chords 
  4. Fully-developed intestinal tract
  5. Separate sexes (males and females)
Features of anisakids in particular:
  1. L3 larva embedded in the wall of the stomach or intestine (or in the peritoneal cavity)
  2. Thick unadorned cuticule
  3. Tall coelomyarian musculature (m)
  4. Splayed, Y-shaped lateral cords (arrow heads). The slender appearance of lateral cords are consistent with Anisakis species.
  5. Prominent esophagus (black asterisk)
  6. Banana-shaped excretory cell (white asterisk)

Tuesday, July 12, 2022

Bedtime Reading?

For those of you looking for some good (?) bedtime reading, you may be interested in two fun articles that Blaine Mathison and I recently wrote:

Blaine A. Mathison, Bobbi S. Pritt, Sleeping with the Enemy: Everything You Need to Know about the Biology, Clinical Significance, and Laboratory Identification of Bed Bugs. Clinical Microbiology Newsletter, Volume 43, Issue 1, 2021, Pages 1-7,

Blaine A. Mathison, Bobbi S. Pritt, Don't Be a Nit Wit; Know Your Lousy Companions! Clinical Microbiology Newsletter, Volume 44, Issue 13, 2022, Pages 115-122,

If you don't have access to these, please drop me a line at and I will send you a copy.

Bobbi Pritt (@ParasiteGal)

Tuesday, July 5, 2022

Case of the Week 688

This week's case features an object (of many) found in the hair of a 6-year-old girl. Identification?

Monday, July 4, 2022

Answer to Case 688

 Answer to the Parasite Case of the Week 688: Nit (egg) of Pediculus humanus capitis. 

As noted by Kosta Mumcuoglu, "it is the egg of the head louse, Pediculus humanus capitis with the embryo inside (legs visible) and the operculum still on the egg. We can also see the part of the glue which was used to attach the egg on the hair. The aeropyles are in a row while in case of the pubic louse eggs they are in a triangular order. See but also Case 293 in Creepy Dreadful Wonderful Parasites. It is by the way Pthirus not Phthirus pubis." 

Kosta is correct on all counts. Here are some of the key identifying features. I find the detail of the embryo within the eggs to be particularly striking. 

The eggs of P. h. capitis are typically glued onto the sheath of a hair, compared to the eggs of P. h. humanus, which are glued onto clothing (and don't have a nit sheath).  

Monday, June 27, 2022

Case of the Week 687

 This week's case is generously donated by Dr. Ioana Bujila of the Public Health Agency of Sweden. The patient is a 67 year old woman from Gabon. Blood was examined by direct mount and Giemsa-stained blood films, and the following were identified:

These objects are approximately 228 micrometers in length.

What is your diagnosis? Are there any additional laboratory analyses that are recommended in this case? 

Sunday, June 26, 2022

Answer to Case 687

 Answer to Parasite Case of the Week 687Loa loa

As noted by Florida Fan, @JuanCGabaldon, Idzi P, Ulrike E. Zelck, Priyanka Gupta, and others, the video clearly shows this to be a sheathed microfilaria, and the Giemsa smear shows the column of nuclei extending all the way to the tip of the tail, thus allowing us to make an identification of Loa loa. The patient's travel history (Gabon) also fits with this identification. 

As Idzi P. mentioned, I like to teach my students that nuclei flow-a flow-a to the tip in Loa loa - a fun learning aid!  Also check out this beautiful infographic by @cullen_lilley for an algorithm to differentiate the  common human-infecting microfilariae. 

Idzi P. further adds "These are by far the most beautiful images I have ever seen from what is definitely Loa loa microfilariae. I especially LOVE the video (second one) where the sheath is nicely visible!"

I agree - the video is amazing, and you should all check it out. 

Idzi P. goes on note that "a Knott's concentration could be envisaged to obtain a quantitative result before treatment is started. Also a hematoxylin-based staining (like Carrazzi's hematoxylin staining) could be used to demonstrate the sheath more nicely (as Luis H. points out: Giemsa does not usually/reliably stain the sheath of microfilariae) and better show the positioning of the nuclei in the tail." This is the answer to my question regarding additional laboratory testing that is indicated. Treatment of Loa loa is quite complicated, and patients with more than 8,000 microfilariae/mL are at risk of fatal encephalopathy with treatment. Therefore, obtaining a parasite count is important for guiding therapy. 

Thanks again to Dr. Ioana Bujila and the Public Health Agency of Sweden for sharing this beautiful case!

Tuesday, June 14, 2022

Case of the Week 686

This week's case was generously donated by Dr. Mike Mitchell and Laura Derderian. The following structure was seen in a stool concentrated wet mount specimen. It measures 27.5 micrometers in length. This was the only structure present in this specimen. Identification? What additional testing might also be useful in this case?

Sunday, June 12, 2022

Answer to Case 686

 Answer to the Parasite Case of the Week 686: Cystoisospora belli sporulated oocyst

This case shows a single - but classic - sporulated oocyst of Cystoisospora (formerly Isospora) belli. Note that two sporoblasts are present in this case, which is unusual to see in freshly passed stool specimens. Most C. belli oocysts are shed in an immature state - either unsporulated or partially sporulated (with only one sporoblast). They mature further in the environment, with the sporoblast dividing in two so that the mature oocyst has 2 sporoblasts. The sporoblasts become sporocysts with a surrounding cyst wall, and the sporocysts divide twice so that they produce 4 sporozoites each. 

We can make the diagnosis based on its characteristic appearance. However, if we wanted to confirm the diagnosis, Florida Fan notes that the oocysts "autofluoresce brightly under UV light excitation and will stain acid fast too." He goes on to say that "our team members prefer the autofluorescent methodology as it is simple and less time consuming." I know of some other labs that also prefer fluorescent microscopy to modified acid fast (MAF) staining since it is more sensitive. 

You can see some great examples of MAF staining HERE, and an autofluorescent oocyst of C. belli  from Florida Fan HERE.

Thanks again to Dr. Mike Mitchell and Laura Derderian for sharing this great case!

Monday, June 6, 2022

Case of the Week 685

 This is week's case is from our long-time contributor, Idzi Potters from the Institute of Tropical Medicine, Antwerp. The following structures were seen in a iodine wet preparation of concentrated stool. Identification? 

Sunday, June 5, 2022

Answer to Case 685

 Answer to the Parasite Case of the Week 685: Raphides, i.e, needle-shaped crystals of calcium oxalate or calcium carbonate used by several plants such as pineapple, kiwi, and rhubarb as a defense against plant-eating animals. According to Idzi, "The weird feeling you get in your mouth when eating too much pineapple is apparently caused by these crystals. You can find them quite often in stools and they should not be confused with Charcot-Leyden (C-L) crystals!" They can be differentiated from C-L crystals by their long needle-like shape and uniform diameter:

As a comparator, Idzi provided 2 nice photographs of C-L crystals, the slender bipyramidal hexagonal crystals of galectin-10. "They were first noticed in 1851 by Friedrich Albert von Zenker, and later on described in detail in 1853 by Jean-Martin Charcot and Charles-Philippe Robin. After that, in 1872, they were further described by Ernst Viktor von Leyden. Hence their name…"

Charcot-Leyden crystals:

Galectin-10 is contained in the granules from eosinophils (and also from basophils) and spontaneously crystallizes into Charcot-Leyden crystals when it is released in the extracellular environment (by exocytosis and/or cellular breakdown). Charcot-Leyden crystals are therefore indicative of eosinophilic inflammation (caused by asthma, allergic reactions, parasitic infections, etc)."

Thanks again to Idzi for this excellent case!

Tuesday, May 31, 2022

Case of the Week 684

 For our last case of May, we have a fun submission from Dr. Megan Shaughnessy. She noted the following in some fresh monkfish she purchased from a small local grocery store. What is the likely identification? Also, what is the risk to humans if ingested?

Monday, May 30, 2022

Answer to Case 684

Answer to the Parasite Case of the Week 684: Anisakid L3 larvae

The following is our third and final discussion from our amazing guest author and 3rd year medical student, Hadel Go. I'm sure you will all agree that her discussions have been among the best we've ever had on this blog. Congratulations on the excellent work, Hadel!


Worm cases are always my favorite because the comments are either “They are so beautiful!!” (@Parasite_Power on Twitter) or “…That’s a wholelottanope” (Valmik in the comments).

This is a nematode in the Anisakidae family, likely Pseudoterranova or Anisakis spp., the two most common cause of human anisakiasis, as many of you suggested. A third genus, Contracaecum, is also a possibility. Mario George Nascimento and Melinh Luong point out that its dark color implicates Pseudoterranova (vs Anasakis which is usually white/pink/red). 

However definitive identification to the genus level requires closer inspection of the intestinal cecum and its positioning as mentioned by Idzi P. in the comments and seen in Case 563 which he donated.

Diagnostic features of Pseudoterranova and Anasakis spp. include a “mucron… and 3 poorly formed anterior lips with a small boring tooth” (see Case 157 and Case 557). The table below shows some varying characteristics between the two more common culprits:


Anisakis simplex

Pseudoterranova decipiens


White, milky



19-36mm long; 0.3-0.6mm wide

25-50mm, 0.3-1.2mm wide

Other features

Blunt tail, long stomach, Y-shaped lateral cords, no cecum

Anteriorly directed cecum


1. Marine mammals defecate into the sea releasing unembryonated eggs
2. Eggs become embryonated in water
3. L2 larvae form in eggs and hatch out
4. Free swimming L2 larvae are ingested by crustaceans and mature into L3 larvae in the hemocoel
5. Fish (any marine fish is susceptible) and cephalopods eat infected crustaceans
6. Larvae migrate to mesentery and muscle tissues of the new host
7. L3 larvae are transferred from fish to fish until ingested by a marine mammal
8. L3 larvae molt twice in the mammal and develop into adults which produce eggs

Anisakiasis occurs when these parasites at the L3 larval stage are ingested in raw or undercooked saltwater seafood. While some larvae will die following ingestion, or make their way up the esophagus into the oral cavity (much to the dismay of the human host!), they may also attach to the wall of the human esophagus, stomach, or intestine causing damage or inflammation. Since humans are incidental hosts, the anisakids do not mature into adults. Symptoms include abdominal pain, nausea, vomiting, distention, diarrhea, blood/mucus in stool, and mild fever. If a patient is allergic to anisakids, rash, itching, angioedema, or anaphylaxis can occur (even when the worms are dead). Complications include intestinal obstruction, peritonitis, and intestinal perforation. Severe immune response following penetration of intestinal tissue can resemble Crohn’s disease.

These roundworms can be visualized and removed with an endoscope, confirming the diagnosis. If not removed, they will eventually die and can cause inflammation. A biopsy can reveal an eosinophilic granuloma containing the dead nematode. Endoscopic or surgical removal of the parasites is curative. Treatment with albendazole has been used successfully to kill the worms, although not FDA approved for anisakiasis. Unembedded worms are usually eliminated by the body within 3 weeks.

Avoid infection by following one of these FDA recommendations which kills the parasite:
- Cook seafood (145°F or above)
- Freeze at -4°F or below for 7 days
- Blast freeze at -31°F or below until solid and store at -31°F or below for 15 hours
- Blast freeze at -31°F or below until solid and store at -4°F for below for 24 hours

I’ve often been asked if I eat sushi and sashimi knowing the prevalence of these worms… and the answer is YES, I love Japanese cuisine and I eat them regularly. All fish intended for raw consumption in the US are required by the FDA to be frozen as stated above so they should be safe. The dead parasites may still be on the tissue, but they won’t be infectious. I would however be more hesitant to eat raw or undercooked fish when traveling to places where there are less stringent regulations. Ask for sushi/sashimi grade fish and use your best judgement!

Kingdom: Animalia
Phylum: Nematoda (roundworms)
Order: Rhabditida
Family: Anisakidae

Read more:
1. CDC - Anisakiasis
2. Anisakidosis: Perils of the Deep | Clinical Infectious Diseases | Oxford Academic (
3. Anisakis, Something Is Moving inside the Fish - PMC (
4. Assessing the risk of an emerging zoonosis of worldwide concern: anisakiasis - PMC (

Thank you @leon_metlay on Twitter for sharing this paper:
Intestinal anisakiasis. Report of a case and recovery of larvae from market fish - PubMed (

This is my third and final post as a guest blogger here and I’d like to thank Dr. Bobbi Pritt for the opportunity to learn more about these creatures and share what I’ve learned with you all!

Monday, May 23, 2022

Case of the Week 683

 This week's case is from a 4 year old boy with sudden onset of 'explosive' watery diarrhea, accompanied by low grade fever, nausea, vomiting, and loss of appetite. A stool specimen was obtained after 1 week of symptoms, and the following objects were noted on a modified acid fast stain. They measure approximately 5 micrometers in diameter. 

Here are some questions to consider:

1. What parasite is shown?

2. Name 3 common ways that infection is acquired.

3. What is the typical recommended treatment?

4. What are the risk factors for severe infection.

As with last week, Hadel Go is serving as a guest author, and will help us answer these questions later this week. Stay tuned!