Monday, October 14, 2019

Case of the Week 564

This week's case was donated by Blaine Mathison and Marc Couturier. The following forms were seen on peripheral blood smears. No travel history is available at this time. How would you recommend reporting out this case? Are there any additional studies you would recommend?

Sunday, October 13, 2019

Answer to Case 564

Answer: Mixed Plasmodium ovale and Plasmodium falciparum infection.

This was a very nice clear-cut example of a mixed infection. Often they aren't this clear cut! Thanks to everyone who wrote in with the very nice morphologic descriptions supporting the diagnosis.

Santiago noted that "The first five images show many diagnostic morphologic features: the infected RBCs are enlarged, they have an oval shape with jagged edges (fimbriations), Schüffner's dots (fine cytoplasmic stippling) are present in their cytoplasm, and infecting trophozoites are compact; these features are consistent with infection by Plasmodium ovale.

The last two images show banana-shaped gametocytes which are diagnostic of Plasmodium falciparum.

My follow-up question was regarding which additional studies, if any, would be recommended. In this case, the morphology is very convincing, and so diagnostic PCR is likely not needed.  However, it was available in this case, and confirmed the diagnosis of P. falciparum and P. ovale mixed infection. Several of you also correctly noted that quantification of parasitemia is also indicated to guide therapy.

Finally, knowing more about the patient would be important to direct patient care. Information to gather would include where the patient had traveled (to determine if there is circulating resistance to commonly-used antimalarials) and if prior antimalarial therapy had been administered. The fact that only P. falciparum gametocytes were present may indicate that the patient had received prior therapy, since the drugs commonly used to treat P. falciparum are not gametocidal. Thus seeing residual P. falciparum gametocytes is not uncommon after successful treatment.  Now that we know that the patient has P. ovale co-infection, primaquine (or tafenoquine) must be administered to eradicate its hypnotzoite stage (dormant stage in the liver).

Thanks again to Marc and Blaine for donating this case.

Monday, October 7, 2019

Case of the Week 563

It's time for our first case of the month by Idzi Potters and the Institute of Tropical Medicine, Antwerp.   The patient is a 50 yo Belgian patient returning from Italy with intestinal complaints coughs up the following worm:


Sunday, October 6, 2019

Answer to Case 563

Answer to Parasite Case of the Week 563: Anisakid larva, not Anisakis species.

As noted by Marc Couturier, this case has a "very nice and clearly defined intestinal caecum [or 'cecum' for my United States readers]. Lips are visible on the worm and the general size would point again to an Anisakidae member. Coughing up and the abdominal pain are helpful clinical correlates as well." Blaine also added some helpful information regarding the diagnostic features of anisakids: "Based on the anteriorly-directed cecum, this is either Pseudoterranova or Contracaecum. Unfortunately it is not possible to definitively tell from the image if a posterior ventricular appendix is present (Contracaecum) or absent (Pseudoterranova). Anisakis species lack both." He also noted that all 3 genera may have an anterior boring tooth.

The arrow in the following image points to the anteriorly-facing cecum.

Thanks again to Idzi for donating this beautiful case. I thought that it nicely complimented last week's case, which had a nice clinical (endoscopy) image but lacked a view of the defining morphologic features.

Monday, September 30, 2019

Case of the Week 562

This week's case was generously donated by Dr. David Hernandez Gonzalo. The patient is a middle-aged male who presented with abdominal discomfort and nausea. An endoscopy was performed which revealed the following object in the gastric antrum:
The worm was sent to pathology and was sectioned, revealing the following (H&E):

Sunday, September 29, 2019

Answer to Case 562

Answer to Parasite Case of the Week 562: Likely anisakid, given the gross and microscopic appearance and position in the body. This also fits with the clinical history that I held back - this patient was an avid sushi lover!

From the gross image, you can tell that this is a roundworm, and that it appears to be embedded in the gastric mucosa:
You can also see that the caliber of the worm is similar throughout its length. That, as well as the location (stomach), make Trichuris trichiura unlikely. The longer length also allows us to rule out Enterobius vermicularis and the hookworms (which admittedly would also be unlikely in the stomach).

The microscopy is a bit harder to interpret, given that we only have a portion of the worm to examine. What we can make out, however, is the thick eosinophilic cuticle, tall coelomyarian musculature with multiple muscle cells (polymyarian), the intestinal tract that runs the length of the visible portion of the section, and the lack of reproductive structures, which are consistent with an L3 anisakid larva:
I believe that the netting like structure is a section through the muscle cells. We unfortunately can't see the lateral cords (best seen in cross-section) and additional features that would help us identify the anisakid to the genus level (e.g., cecum). This brings us to the conclusion that we always draw from this case, which is to send the worm to the microbiology lab and not the surgical pathology bench!

From Blaine:

Why are pathologists so quick to slice-and-dice
When a diagnosis would be much more precise
If they just left it intact
and the microbiologists have a whack
Alas now a diagnosis is a roll of the dice

Monday, September 23, 2019

Case of the Week 561

This week's case features photos and videos from my fabulous Technical Specialists, Heather Arguello and Emily Fernholz. The following were seen in bronchoalveolar lavage fluid. Identification?

Sunday, September 22, 2019

Answer to Case 561

Answer to Parasite Case of the Week 561: Strongyloides stercoralis L3 (filariform) larvae.

As noted by Florida Fan, the notched tail is clearly shown in this case. Indeed, this is the best example I've ever seen. The notched tail can be used to differentiate the L3 larvae of S. stercoralis with those of hookworm (the latter has a pointed tail).
Old One also pointed out that the filariform esophagus reaches to the midpoint of the S. stercoralis L3 larva. In comparison, the esophagus only reaches to ~1/3 of the hookworm L3 larva. (The CDC has a nice schematic of these differences which you can view HERE.) I can't tell if the background cells in the current case are eosinophils, but peripheral and local eosinophilia are common features of strongyloidiasis.

BW in VT noted that the patient may have acquired infection years ago, and maintained infection via ongoing autoinfection. This is an important component of the S. stercoralis life cycle, as it allows for infection to persist for decades. Should the patient become immunocompromised, the ongoing infection can produce a hyperinfection state, leading to severe morbidity and possible death.

From Blaine: Silly stringy Strongyloides stercoralis stealthily slithers in sputum, spied by sensational Specialists.

Monday, September 16, 2019

Case of the Week 560

This week's case is a composite photo I created for my 2019 calendar for the month of September. The accompanying questions are:

  1. What is the parasite shown? (measure ~60 micrometers long)
  2. Why is this a suitable parasite for September?
  3. What is the significance of the other objects in the picture? 

Sunday, September 15, 2019

Answer to Case 560

Answer to Parasite Case of the Week 560: "Back to school" pinworm

This fun image had a question in 3 parts:
  1. What is the parasite shown? Eggs of Enterobius vermicularis
  2. Why is this a suitable parasite for September? September is the time that kids go back to school in America, and thus are more likely to obtain easily-transmitted parasites such as pinworm and head lice. As Nema noted, pinworm is "a parasite that is transmitted efficiently at the start of the school year because the embryonated eggs easily pass from the hands (unwashed) from one child to another and can also pass through the fomites"
  3. What is the significance of the other objects in the picture? The backpack full of school supplies gives you the "back-to-school" link, whereas the tape refers to the cellulose tape method in which clear (not frosted!) tape is applied to the perianal skin folds to collect eggs (and occasionally adult females) that may be present. This test is commonly called the "Scotch" tape test in the U.S. after a common brand of tape; in the UK, it may be referred to as the Sellotape method - another common local brand.
In my lab, we prefer to use a plastic paddle with an adhesive surface to more efficiently and safely sample the perianal skin (a.k.a. the 'bum paddle' according to Marc). The paddle is easily transported to the lab inside the accompanying tube, and can then be examined directly under the microscope. The Graham test is another commercial collection method available in Europe.

Monday, September 9, 2019

Case of the Week 559

We're one week late due to my crazy travel schedule, but without further delay, here is our monthly case by Idzi Potters and the Institute of Tropical Medicine, Antwerp. It's short and sweet: The following was found in a stool specimen from a 3 year old child with diarrhea. It measures approximately 80 micrometers in diameter. Identification?

Sunday, September 8, 2019

Answer to Case 559

Answer to Parasite Case of the Week 559: Hymenolepis diminuta
This was another great case by Idzi Potters. This egg had all of the characteristic features of H. diminuta: large size (80 microns), and lack of polar filaments between the striated outer membrane and the smooth inner membrane.You can also nicely see some of the hooks of the internal 6-hooked oncosphere:
Here is a side-by-side comparison of H. diminuta eggs, and the eggs of the related cestode, Hymenolepis nana. You can see that they are very similar appearing, but H. nana eggs are smaller and have polar filaments that originate from the inner membrane and extend out into the space between membranes (arrows in image below).
Some pondered why the parasite featured this week was named "diminuta" since its eggs are bigger than those of H. nana. Blaine helped us with that answer to this: "H. diminuta was described earlier (1819) then H. nana (1851). So, at the time of its description, H. diminuta may have been the smallest tapeworm known from humans. "Nana" comes from the Latin 'nanus' meaning dwarf or small." Isn't etymology fun?

A fun saying for today: People who confuse etymology and entomology bug me in a way I can't put into words 

Wednesday, August 28, 2019

Case of the Week 558

This week's case presents a bit of a conundrum. The patient is a 50 year old woman with recent travel to Kenya. She presents with acute onset of fever and chills and was tested by a rapid malaria antigen test (P. falciparum and Pan-malaria antigens) and was negative. A follow-up Giemsa-stained thin blood smear from the same blood collection shows the following:

Identification based on the blood smear? How might this correlate with the rapid antigen test?

Sunday, August 25, 2019

Answer to Case 558

Answer to Parasite Case of the Week 558: Plasmodium falciparum malaria, >10% parasitemia. NEGATIVE rapid antigen.

So why is the rapid antigen test negative???

As noted by our readers, there are many possible reasons for a positive blood smear and negative rapid malaria antigen test (RDT). Here are our options, along with the reasons why each is or isn't a likely explanation in this case:
  1. This is babesiosis, and not malaria. This is a very important consideration given the morphologic similarities between Babesia spp. and Plasmodium falciparum. However, the moprhologic features in this case are highly consistent with P. falciparum, including the presence of relatively-homogenous rings, without the size and shape pleomorphism usually seen with Babesia spp. There are also applique forms and headphone forms (arrows, below) which are characteristic, but not definitive, for P. falciparum infection. There may also be a hint of hemazoin (malaria pigment), but it is not obvious. Overall, we can rule out babesiosis based on the microscopic morphology.
  2. The negative RDT is due to deletion of the P. falciparum histidine rich protein II repeat region in the parasite infecting this patient. This deletion has been reported in some African and South American countries, including Kenya where this patient had recently traveled. While this is a good thought, it would not explain why the pan-malaria antigen band (in this case, aldolase) is also absent, resulting in a completely negative RDT result. Thus, we can also exclude this as the reason for the negative RDT. 
  3. This is the well-described prozone (or 'hook') phenomenon, where antigen excess (seen in cases like this with high parasitemia) binds to both the capture and detection antibodies and interferes with the formation of an antibody-antigen-antibody 'sandwich'. (You can refresh your memory on how a lateral flow immunoassay works by reading this fairly well-written Wikipedia article on malaria RDTs HERE). Prozone effect is well-described for malaria RDTs. You can read a nice study on how often this might occur HERE. In my mind, this is the most likely cause of the false negative result seen in this case.
  4. The kit is faulty, or the test was not performed correctly. We unfortunately can't rule this out.
What additional testing would help us sort out the cause of the false negative RDT?

As some of you mentioned, confirmatory testing by another method would be useful to prove this was indeed malaria. Fortunately, we were able to perform PCR and it was strongly positive for P. falciparum, thus confirming our microscopic impression. To evaluate for possible RDT prozone phenomenon, we could also test serial dilutions of the fresh blood specimen to see if specimens with diluted antigen become positive. Repeat RDT testing would confirm that the test was performed correctly to begin with. Finally, we could easily confirm that the test kit isn't expired by checking the box that was used, and checking the storage conditions to ensure that they were appropriate for the test kits.

While we don't have a definitive answer for this case, I thought it was an excellent opportunity to discuss how the prozone phenomenon is a real risk in cases of high malaria parasitemia and may result in false negative results. This is one reason why malaria RDT results should always be followed gold standard blood film examination (or PCR). Also, we always need to remember that no lab test is perfect, and must always be interpreted in the context of the individual patient. 

Thank you all for the excellent comments and discussion on this case!

Sunday, August 18, 2019

Case of the Week 557

This week's case was donated by Florida Fan and one of his coworkers who found this beauty in some fresh salmon:
Posterior end:
 Anterior end:

Saturday, August 17, 2019

Answer to Case 557

Answer to Parasite Case of the Week 557: As mentioned by Bernardino Rocha, this is either an L3 larva of the Anisakidae or Raphidascarididae - 2 families of nematodes that are commonly found in fish. I tend to agree with Blaine and Bernardino that this is most likely a Type I Anisakis or Pseudoterranova sp.; however, we would need to see its internal features to be sure (you can read the comments to learn how to clear the worm to visualize its internal structures). As Blaine mentioned, the presence of the mucron (the terminal spicule-like structure shown below) rules out Contracaecum spp. and Type II Anisakis. Other morphologic features that can be used to differentiate Anisakis, Pseudoterranova, and Contracaecum species are the features of the ventriculus, the number of intestinal cells in cross section, and the shape of the lateral chords (also seen in cross-section).

Blaine Mathison and Alex da Silva recently wrote an excellent chapter on Anisakiasis in Ortega's and Sterling's book entitled "Foodborne Parasites" (email Blaine if you want more information).

Thanks again to Florida Fan for donating this nice case of an anisakid nematode, with nice visualization of the anterior boring tooth and mucron. It serves as an excellent reminder to us all to cook your fish thoroughly before eating it! For the sushi lovers out there, you can kill all parasites in raw fish by freezing it for 7 days at -20C. Bon appetite!

Monday, August 12, 2019

Case of the Week 556

This week's case was donated by Dr. Neil Harris and Dr. Stacy Beal. The patient is an infant with a history of tracheobronchomalacia and "eosinophilia" on prior bronchoscopy. A routine complete blood count was negative without evidence of peripheral eosinophilia. The following structures were seen on a Giemsa-stained bronchoalveolar lavage specimen using the 100x objective. They have a diameter of 1-3 micrometers. Identification?

Sunday, August 11, 2019

Answer to Case 556

Answer to the Parasite Case of the Week 556: Curschmann spirals

Curshmann spirals can be a very pretty, but sometimes confounding parasite mimic in sputum, BAL and bronchial lavage specimens. They are spiral-shaped plugs of mucus from obstructed bronchioles, and are seen in patients with asthma and other conditions affecting the airways (e.g. tracheobronchomalacia as seen in this case). Although they can take on a roundworm-like appearance, they can be differentiated by their lack of defined morphologic features such as a cuticle and internal structures. Here is a striking photo from a different case (Papanicolaou stain):

Friday, August 2, 2019

Case of the Week 555 - a Special Challenge!

Dear readers,
I am excited and humbled to be posting my 555th Parasite Case of the Week. I am continuously inspired by your comments, questions, and the rich discussion that occurs with each post. To mark this occasion, I'm asking you all to comment on ways that parasites relate to the number 5. I'll start you off with two that were previously suggested to me when I thought up this challenge:
  1. Pentatrichomonas hominis is a nonpathogenic intestinal flagellate named for its 5 flagella (penta from the Greek pente, meaning five + trich, pertaining to hair [flagella]). By Dr. Neil Anderson
  2. There are 5 lobes of the human lung, and all can be infected by Paragonimus species. By Brian Duresko
Feel free to be as creative as you'd like. 5-lined poems (e.g. limericks) are also accepted! I will post all of the responses next Friday, so you have all weekend and next week to think of ideas. Enjoy!

Thursday, August 1, 2019

Answer to Case 555 - Parasites and the Number Five

Wow - we received so many excellent comments on how parasites and the number 5 go together! Here are many of them - in no particular order - for your viewing pleasure:
  1. Pentatrichomonas hominis is a nonpathogenic intestinal flagellate named for its 5 flagella (penta from the Greek pente, meaning five + trich, pertaining to hair [flagella]). By Neil Anderson and Bernardino Rocha.
  2. There are 5 lobes of the lung, and all can be infected by Paragonimus species. By Brian Duresko.
  3. The are 5 Plasmodium species that are responsible for the bulk of malaria in humans: P. falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi (the latter is a zoonotic parasite and important cause of malaria in regions of SE Asia). By Aimee Boerger, Nipunie Rajapakse, and LS.
  4. Pentastomes have a name meaning "five openings". Although having a single mouth, there are 2 pairs of hollow fang-like hooks beside the mouth. These fangs can be retracted into slits giving the appearance of 5 mouths. By Old One.
  5. Quintan fever, also known as trench fever, is due to infection with the bacterium Bartonella quintana, and is transmitted by the body louse, Pediculus humanus humanus. The infection is characterized by fevers that recur every five days; hence the name of the bacterium and the resultant disease. By Kristin Nagaro.
  6. The gametocytes of Plasmodium vivax appear in the blood ~5 days after the liver stage, whereas it takes 10-12 days for P. falciparum to appear. Thus, P. vivax infection can be acquired by mosquitoes at the very first blood stage cycle, and this may confer a transmission advantage for P. vivax over P. falciparum. Plasmodium vivax has the most widespread distribution of the human malaria-causing Plasmodium spp., and the early gametocytemia will have important implications for malaria eradication. By BW in Vt.
  7. Pentamidine is a drug used to treat some protozoal infections such as leishmaniasis and African trypanosomiasis. The first part of the drug's name comes from the pentane component which has 5 carbon atoms (C5H12). By Andy Norgan.
  8. Human parasites can be divided into 5 major groups: protozoa, platyhelminthes, acanthocephala, nematoda, and arthropoda. By Bernardino Rocha.
  9. The 5 main symptoms of giardiasis are diarrhea, abdominal pain, fatigue, weakness, weight loss. By bks. I use a similar one - the 5 "F's" of giardiasis: Foul-smelling Fatty Feces that Floats and Flatulence.
  10. The US Centers for Disease Control and Prevention has targeted 5 neglected parasitic infections (Chagas disease, neurocysticercosis, toxocariasis, toxoplasmosis, and trichomoniasis) as priorities for public health action, based on the numbers of people infected, the severity of illnesses, or our ability to prevent and treat them. Anonymous.
  11. Toxoplasmosis, a protozoal infection, in one of the ‘infamous 5’ TORCH infections that cause congenital abnormalities; the acronym stands for Toxoplasmosis, Other (syphilis, VZV, parvovirus b-19), Rubella, CMV, and Herpes simplex virus infections. By Vik Holenarasipur and Anonymous.
  12. Human bot flies (and other insects) have 5 eyes - 2 are compound and 3 are simple. This paper wasp (below) is not a parasite, but was willing to pose for a photograph of its five eyes. By John Carlson (@JohnCarlsonMD).
There were also some wonderful stories and poems with 5 lines or words/line:
From Blaine Mathison:

Many of the earth-based religions use the pentagram to represent the Five Elements: Spirit, Air, Water, Earth, and Fire. Many religious beliefs are grounded in scientific phenomena that were unknown at the time. What many people do not know, is the earth religions are rooted in Parasitology!

Spirit represents Loa loa and its microfilariae that circulate in the body. This belief is shared with Voodoo as the term 'loa' is a spirit in Voodoo religion.

Water represents Schistosoma, as water is natural reservoir for which the spirit enters the body.

Fire represents Trichomonas vaginalis, as people occupied by this spirit often have a burning sensation.

Earth represents Strongyloides stercoralis as they enter the body from the soil. Some liken Strongyloides to Mother Earth as she can create life in a host without a male counterpart.

Air represents Plasmodium, as it is carried by flying arthropods! And its erythrocytic cycle created periods of suffering and relief, as a reminder Life is a balance of Good and Evil.

If you have read this far, yes I am being silly and having fun, letting the creative juices overflow a bit :-D
From Old One:

Now in Rochester’s sunny clime
Where I used to spend me time
A-servin’ the majestic Clinic Mayo
Of all that brilliant crew
The finest Doc I knew
Was Dr. Pritt, Diagnostic Mistro

It was Dr. Pritt, Pritt, Pritt
Most skillfull Parasite Gal, Dr.Pritt
Hi! Slippy Hitherao
Diagnosis please, Panee Lao
And be quick, about it. “Lickety split” Dr. Pritt

This noble Parasite Gal
Has a blog that’s really swell
Which has been followed round the globe for many years
She’s now at 555
And if I stay alive
I expect to see 666. Note to Satan, please stand clear

If I’m ever on campaign
Licking boots and water green
I will make tracts to Dr. Pritt at Mayo Clinic
She’s the one to check my blood and stool
Mama didn’t raise a fool
For I’ll surely have a case most parasitic
Also from Old One:

Zen queries to Madam Ascaris
What is the sound of one hand clapping?
What does a three lip smile look like?

A happy worm is the ascarid
Swims in chyme and squirms like a squid
As happy as she is
She has but one regret
“How do you smile with three lips on the tip of ones head?”
From Sir Galahad,
5 verses of J.Swift:

Big fleas...
Big fleas have little fleas
Upon their backs to bite' em
And little fleas have lesser fleas
And so, ad infinitum

(Filastrocca di Jonathan Swift
Disegno di Robert Hegner, 1938)

Monday, July 29, 2019

Case of the Week 554

This week's case was generously donated by Florida Fan. The following are seen on Giemsa-stained thick and thin blood films. No history is immediately available. Diagnosis? Any additional information you would like?

Sunday, July 28, 2019

Answer to Case 554

Answer to Parasite Case of the Week 554: Babesia species. Without a travel history, the differential diagnosis includes Plasmodium falciparum malaria given that only ring forms are seen and there is a high parasitemia; however, the following features are supportive of babesiosis:
1. Multiple (4) small forms within a single cell that are not a clear schizont form of Plasmodium.
2. Easily-identified extracellular forms.
3. Lack of malaria pigment

As Blaine mentioned, the rings are not thin and delicate as would normally be seen with P. falciparum infection. While thicker rings are commonly seen in 'older' blood (i.e., blood that was >24 hours old), we would expect to see malaria pigment in these cases, and none is seen in this case.

One reader was favoring babesiosis, but was swayed from this diagnosis by the lack of maltese cross (tetrad) forms. However, it's important to note that most cases of babesiosis will NOT have maltese cross forms. Instead, the diagnosis must be made on the other features listed above, in addition to the commonly-seen pleomorphism of the parasite forms in babesiosis. Interestingly there wasn't a lot of pleomorphism in this case.

Thanks again to Florida Fan for donating this informative case. It reinforces the need to get a travel history whenever possible (he later learned that the patient had not traveled outside of the United States), and to consider both babesiosis and malaria in the differential when seeing intraerythrocytic parasites.

Monday, July 22, 2019

Case of the Week 553

This week's (interesting but somewhat disturbing) case was generously donated by Dr. José A. T. Poloni. The following was submitted from a fresh (unfixed) stool specimen. Most likely identification?

Sunday, July 21, 2019

Answer to Case 553

Answer to Parasite Case of the Week 553: Ascaris lumbricoides

The overall appearance and large size of this nematode are strongly suggestive of A. lumbricoides, given that this is a human stool specimen. As Sam mentioned, examining the anterior end for the characteristic 3 fleshy lips common to all ascarids, and examination of the stool for eggs would allow for confirmation of the identification.

Here are some images from other cases to show these characteristic features:
Adult with 3 fleshy lips from Case of the Week 479:
Mammillated and decorticated eggs from Case of the Week 550

Thanks to all that wrote in with the answer, and to Dr. Poloni for donating this case!

Monday, July 15, 2019

Case of the Week 552

This week's case is from Blaine Mathison. The following were seen on a trichrome-stained stool specimen. They averaged 5 to 7 micrometers in greatest dimension. A Giardia antigen test was positive.