Case of the Week 773

This week's case is generously donated by Dr. Rasool Jafari from the Department of Parasitology and Mycology, School of Medicine, Urmia University of Medical Sciences, Urmia, Iran. These objects were isolated from a patient and cultured in Modified TYI-S-33 medium. What parasite is this, and what are we seeing here?

Answer to Case 773

Answer to the Parasite Case of the Week 773: Giardia duodenalis trophozoites with 'falling leaf' motility. As nicely described by Idzi,this is a "Beautiful video material of Giardia trophozoites! Note that it’s official name now is “Giardia duodenalis”. We used to cultivate these critters on Keisters medium for educational purposes. Not easy though, so the more impressing this video by Dr. Rasool Jafari is! Kudos!"

Indeed, you can make out multiple characteristic features of Giardia trophozoites, including the 'tear drop' shape with 2 nuclei and a central axoneme when viewed anteriorly, a concave spoon-shaped appearance when viewed from laterally, anterior sucking disk, and even some trophozoites dividing by binary fission. I believe I've captured one here but defer to Dr. Jafari for confirmation. Many thanks again to Dr. Jafari for sharing this interesting case with us.

 

Case of the Week 772

This week's case is generously donated by Dr. Evis Nushi who identified the following structure in direct microscopy of skin scrapings. What is seen here? 

Answer to Case 772

 Answer to the Parasite Case of the Week 772: Demodex folliculorum

This little mite, also known as the follicle mite, is a common skin commensal and incidental finding in this case. I initially thought it was a larva emerging from an egg, but on closer examination realized that it is a more mature form (with 8 legs rather than the 6 found in the larval stage) and that it's posterior end is twisted around. I've done my best to demonstrate this here:

Thanks again to Dr. Evis Nushi who donated this fun case!

Case of the Week 771

This week's case was generously donated by Dr. Emily Snaverly. The following images show an incidental finding from screening colonoscopy, measuring approximately 1cm long. The patient is an asymptomatic, middle-aged male with no known travel history whose previous colonoscopy did not show any parasites. What is your identification?

Answer to Case 771

Answer to the Parasite Case of the Week 771: Rodentolepis (Hymenolepis) nana, the dwarf tapeworm

As nicely described by Florida Fan, Idzi Potters, and Menzler, the craspedote positioning of the proglottids, armed rostellum, and characteristic (although immature) eggs with prominently splayed, large hooklets all point to R. nana. If you look very closely, you can make out the polar filaments:

Thanks again to Dr. Snaverly for donating these beautiful photos!

Case of the Week 770

This week's case is from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following structures were seen in a stool specimen from a child living in a rural area of Laos. They measure approximately 60 micrometers in greatest dimension. What is your identification?

Answer to Case 770

 Answer to the Parasite Case of the Week 770:  Schistosoma mekongi

The following excellent discussion is by our guest author, Dr. Asra Hasan:

This week’s answer is Schistosoma mekongi! With that, we’ve shown a Schistosoma trio already for the new year—S. haematobium, S. mansoni, and now S. mekongi. Great job, Florida fan! You correctly spotted the inconspicuous lateral spine and the internal miracidium of S. mekongi. And a shoutout to our anonymous writer—your answer was pretty close, as S. mekongi looks a lot like S. japonicum, just smaller, and with a slightly different geographic range. 

The endemic area for S. mekongi is along the lower Mekong River—Laos, Thailand, and Cambodia—hence, the population at risk is comparatively smaller than for other Schistosoma species.

Have a read of the clinical vignette below:

“A 42-year-old male rice farmer from a rural village in Cambodia presents to a local clinic with complaints of chronic diarrhea, abdominal pain, and progressive weight loss over the past six months. He also reports intermittent fever and generalized weakness. On examination, he has hepatosplenomegaly and mild ascites. Laboratory results reveal eosinophilia, and stool microscopy shows small, subspherical eggs with a minute lateral spine at one end. The patient has frequent exposure to river water while working in the fields.” And that would qualify as a typical case for this week—S. mekongi!

The life cycle is similar to other Schistosoma species discussed on this blog (for example, Case 766), except that the definitive hosts are both humans and dogs, and the intermediate host is the snail Neotricula aperta. S. mekongi primarily affects the intestines, liver, and spleen, and rarely, disseminated sites such as the brain.

Diagnosis

Microscopic examination of stool after sedimentation concentration is used to detect eggs.

Antigen tests: Point-of-care lateral flow assays detecting CCA are used for field screening. In the lab, ELISA has been used to detect circulating schistosome antigens in serum and urine and may be the preferred method for confirming diagnosis. Since stool examination can detect schistosome eggs weeks after cure, detection of circulating antigens (CAA & CCA) in blood or urine provides evidence of an ongoing active infection, as both antigens are rapidly cleared from circulation.

Antibody tests can detect evidence of infection, but cannot distinguish current from past infection, and are not particularly useful due to cross-reactions with other helminth infections.

Treatment

Praziquantel is the drug of choice.

Prevention of schistosomiasis involves universal treatment campaigns and that has shown dramatic decrease in disease burden although it has not been helpful in eliminating the disease completely requiring repeated campaigns. Travelers can prevent schistosomiasis by avoiding bathing, swimming, wading, or other contact with freshwater in disease-endemic countries.

And finally, a mention about the World Health Organization. The World Health Organization's roadmap for eliminating neglected tropical diseases recommends targeting Schistosoma mekongi for elimination. Current strategies in affected communities include: Preventive chemotherapy targeting at-risk populations (e.g., entire villages along the Mekong) and distribution of information and education, improvements in water, sanitation, and hygiene.

Some more reading:

CDC resources: https://www.cdc.gov/schistosomiasis/resources/

Case of the Week 769

This week's case is from Idzi Potters and the Institute of Tropical Medicine, Antwerp. The following object was identified in a stool specimen following the glycerin sedimentation technique. It measures approximately 150 micrometers long. How would you sign this case out?

 

Answer to Case 769

Answer to the Parasite Case of the Week 769:  Live Schistosoma mansoni ova. Note the motile miracidium with its characteristic 'flame cell' - a specialized cell that is part of its excretory system, characterized by a flickering, flame-like movement of cilia which helps to expel waste products from the egg (see image below, and be sure to check out the video HERE.

The following excellent discussion is written by our guest author, Dr. Azra Hasan:

Everyone rightly recognized the oval egg with a” lateral spine”, the hallmark feature of Schistosoma mansoni.

Sometimes, it may be necessary to tap the coverslip to move the eggs; the lateral spine may not be visible if the egg is turned on its side. In very light or chronic infections, eggs may be tough to detect in stool; therefore, multiple stool examinations may be required and a biopsy and/or immunologic tests for antigen or antibodies help diagnose infection in these patients.

Schistosomiasis (also known as bilharziasis) spreads when people come in contact with freshwater contaminated by microscopic swimming cercariae released from infected snails. These cercariae penetrate intact skin and mature into adult worms as shown in the life cycle below. Schistosoma mansoni is endemic in Africa, South America, and the Caribbean. Humans are the definitive host and snails (Biomphalaria spp.). are the intermediate hosts. Adult worms reside in blood vessels of the intestines, laying eggs that trigger inflammation, fibrosis, and organ damage.  

 Clinical features

• Acute: 
• Cercarial dermatitis follows skin penetration by cercariae. Stronger reactions may be seen in previously-sensitized hosts.
• Katayama fever is characterized by fever, cough, malaise, and diarrhea (Acute hypersensitivity reaction to the migrating larvae of S. mansoni, also seen in S. japonicum and S. mekongi)
• Chronic: 
• Eggs are deposited in the mesenteric venous system and enter the intestinal wall and liver where they trigger an eosinophilic granulomatous host response, resulting in bloody diarrhea. 
• While some eggs are excreted in the stool, many remain trapped in the tissue. 
• Over time, chronic inflammation leads to fibrotic changes in the liver, with rigid portal veins, and portal hypertension with hepatomegaly. 
• Rarely, schistosomiasis may present as neuroschistosomiasis (seizures, paralysis) due to ectopic eggs (usually associated with S. japonicum). 

Fun Facts:

• Schistosoma is an ancient foe. Schistosoma eggs were found in 3000-year-old Egyptian mummies!  
• Clingy Couple: We have seen the female worm residing in the male’s gynecophoric canal. Did you know this is a lifelong “embrace”?
• Undercover agent: These parasites coat themselves in human proteins to hide from the immune system.
• Egg factory: A female S. mansoni will produce ~300 eggs per DAY  

Treatment: 

Praziquantel is the gold standard. Oxamniquine is effective only against S. mansoni. Resistance to both these drugs has been reported. Early treatment prevents portal hypertension and related complications

Prevention with improved sanitation and avoiding wading in insanitary water, is better than cure! (Praziquantel kills adult worms but not immature larvae- It is important to note that If treatment starts early, always follow up with retreatment). 

Salmonella-schistosome syndrome: When a secondary bacterial infection (usually Salmonella) occurs, anti-schistosome and antibacterial therapy should be given together; the disease remains if the schistosome is not treated simultaneously.

Some interesting case reports:

1. Ectopic Eggs: Hepatic granulomas mimicking cancer in a Brazilian man                                               (DOI: 10.1016/j.ijid.2020.09.1436).
2. Cardiac Schistosomiasis: A rare case of a 25-year-old man in Ethiopia with chest pain and heart failure was found to have S. mansoni eggs in myocardial tissue during autopsy. (PMID:32534906)   
3. Schistosoma Appendicitis- A case report of a 12-year-old Kenyan boy with acute appendicitis who had his appendix packed with S. mansoni eggs. (PMID 34840930)
4. Pulmonary Hypertension- A 35-year-old Brazilian woman with chronic cough and fatigue had S. mansoni eggs in lung biopsies, leading to severe pulmonary hypertension                                                    DOI: 10.1183/13993003.congress-2019.PA5392
5. The Traveler’s Nightmare- A German backpacker developed acute neuroschistosomiasis after swimming in the Nile. MRI showed spinal cord inflammation from ectopic eggs! (PMID:29232415)
6. Rectal Prolapse in a Child: A 4-year-old Ethiopian girl with chronic rectal prolapse had S. mansoni eggs in rectal biopsies. Parasites weaken tissues over time! (PMID:31462942) 

- Paste the PMID number in PubMed for full-text articles

- Type ‘Schistosoma’ in the search bar of this blog and walk through the pages for more images and reads.

Case of the Week 768

This week's case was generously donated by Dr. Mike Mitchell. The following organism was found in the agar of a bacterial urine culture. It is about 1.5 mm in greatest dimension. Would you report this finding, and if so, how? 

Answer to Case 768

Answer to the Parasite Case of the Week 768: Non-parasitic psocid (booklouse/barklouse). In case you were wondering, Psocid is pronounced SO-sid.

Many thanks to everyone on social media and the blog comments, including Florida Fan, Idzi, and Blaine. 

Idzi noted " Definitely a book louse (psocid). Possibly Liposcelis sp. (Order Psocodea - suborder Troctomorpha - Family Liposcelididae). Although these insects resemble lice, these critters are not true lice, not even parasites! They live in moist places and feed primarily on molds, fungi, starch, etc. They can be easily recognized by that funny weird "nose" (or "clypeus" in scientific terms) they have."

Idzi further suggested "...not to report this, as it concerns in incidental find or a contaminant. If found on a more regular basis, try to eliminate the source of contamination as quick as possible."  It's likely that it was introduced into the specimen or the agar plate from the environment. 

I laughed out loud at some of the clever comments I received:

Jefferson Vaughan: I love those little guys. So humble. So innocuous..except to librarians"

James Richardson: "Risk factor-reading on the toilet?" 

Case of the Week 767

This week's case was donated by Drs. Michael Mitchell and Theresa Smith. The following structures were seen on a Papanicolaou-stained anal Pap smear who had a history of squamous dysplasia. They measure approximately 55 micrometers long. What is your diagnosis?

Answer to Case 767

 Answer to the Parasite Case of the Week 767: Enterobius vermicularis egg

The following discussion is written by our outstanding guest author, Dr. Azra Hasan:

The image shows the classic "D-shaped" (plano-convex) egg of E. vermicularis, round on one side and flattened along the other, measuring 50-60 µm × 20–30 µm, containing a folded larva. 

Followers correctly identified the characteristic plano-convex-shaped egg of Enterobius vermicularis, commonly known as the pinworm, named for the pointed, pin-like tail of the female adult worm. Finding parasitic ova on pap smear is not uncommon and in this case the location (anal pap test), shape, and size, strongly point to Enterobius vermicularis.

The following amazing images from another case show a larva hatching from the egg! Many thanks to Dr. Kristin Galan for donating this image, and to Dr. Nicole Brammer Hubbard for coordinating its inclusion in this blog. 

Pinworm infections are exceedingly common worldwide. As Dr. Derrick Jelliffe, a renowned British pediatrician, once quipped, “You had this infection as a child; you have it now; or you will get it again when you have children!” This highlights that although the infection spans all age groups, it is very common in children aged 5–14 years. 

The parasite thrives due to its easy mode of transmission. It is transmitted through anus-finger-mouth contact, nail-biting, unsupervised body hygiene, poor compliance with basic hand hygiene, soiled nightwear, rarely through airborne eggs, and often by fomites such as contaminated furniture, toys, etc.

________________________________________

Life Cycle of Enterobius vermicularis

The cycle begins when a human host ingests embryonated eggs, often contaminated fingers or fomites. The eggs hatch in the small intestine, where larvae undergo two molts to become adult worms. Adult worms then migrate to the large intestine, primarily making the cecum, appendix, and ascending colon their home. 

However, the males mostly die here and pass out in the stool. The gravid female leaves this safe residence every night to travel to the perianal folds to lay her eggs (oviposition).

(If you’d like to see a pretty gravid female pinworm, have a look at the video uploaded on Case 732.)

The cycle completes when scratching transfers eggs from the anus to the mouth, (autoinfection). 

Retroinfection may also occur, with larvae re-entering the rectum.

(Don’t miss the poem by Blaine Mathison, Case 526, on Mrs. Pinworm’s travel and mission.)

________________________________________

Clinical manifestations and a story

The typical symptom of enterobiasis is intense pruritus in the perianal region, especially at night. This occurs due to the nocturnal migration and egg deposition by the female worm.

Severe infections can lead to irritability, disturbed sleep, and secondary bacterial infections from persistent scratching. While the adult female typically resides in the large intestine and moves sporadically to the anus, she may sometimes migrate into ectopic sites such as the female genitourinary tract, causing vulvovaginitis. Several case reports describe various ectopic locations, such as fallopian tubes, omentum, peritoneum, liver, lungs, spleen, and kidneys. Granulomas often form around degenerating worms and eggs in these locations and appear as nodules.

Speaking of ectopic sites and pinworms, I’m instantly reminded of a case I had encountered during residency. A child had come to the ophthalmology clinic with a red, inflamed eye, blurred vision, and intermittent throbbing pain. A live, wriggling worm was found in the conjunctival fold during examination. This was sent to the lab, and, the culprit turned out to be an adult female Enterobius vermicularis. That memory has stayed with me ever since! The ectopic location was caused by the transfer of worms and eggs to the eye through contaminated fingers. Dr. Pritt published a similar case with her fellow, Dr. Esther Babady, back in 2011.

________________________________________

In the Laboratory: 

1. Cellulose acetate tape test (Scotch tape test in the US, Sellotape test in the UK, named after the brand) is the diagnostic method of choice. The paddle test is very simple and user-friendly. It is a neat commercially prepared diagnostic tool that uses a plastic paddle coated with adhesive to collect eggs from the perianal region for the microscopic examination. 

2. As the female worm’s migration is sporadic, more than one test is recommended to rule out infection. Tests are best performed early in the morning before the patient washes or bathes.

3. While adult worms or eggs may occasionally appear in stool, this is incidental; stool samples are not the specimen of choice.

________________________________________

Let the Parents Know:

• Pets at home, such as dogs or cats, do not carry the pinworm.

• Swimming pool chlorination will not eliminate pinworm eggs.

• Cockroaches can serve as mechanical vectors of the eggs—get rid of any in your home.

• Emphasize proper hand hygiene, including techniques, duration, and the 

    role of fingernails in the spread of the infection.

________________________________________

Prevention and Treatment:

Prevention focuses on personal hygiene: frequent handwashing, trimming nails, and cleaning and disinfecting contaminated surfaces such as bedding, clothing, and toys.

Medications such as albendazole and mebendazole are effective for treatment. However, reinfection is common due to environmental contamination. Family members and close contacts are often treated as well. For stubborn cases, a prolonged treatment regimen may be needed.

________________________________________

Some Interesting Reads on Pinworm:

1. The Diagnosis and Treatment of Pinworm Infection, Dtsch Arztebl Int, 2019.

2. Enterobius vermicularis in the Nose: A Rare Entity, Indian J Otolaryngol

     Head Neck Surg, 2005.

3. Large Bowel Obstruction Secondary to Enterobius vermicularis Pseudotumor, BMJ 

     Case Rep. 2022 Nov 29;15(11): e252676.

4. Enterobiasis as a Neglected Worldwide Disease: A Call to Action, Rev Soc Bras Med Trop.

     2024 Oct 28;57: e011022024.

5. The Cockroach as a Host for Trichinella and Enterobius vermicularis: Implications for 

      Public Health, Hawaii Med J. 2004 Mar;63(3):74-7.

6.  CDC: http://www.cdc.gov/parasites/pinworm/

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Case of the Week 766

This week's case is a nice straight-forward one for a change! The following objects were found in a urine specimen and measure ~150 micrometers in length. What is your identification? Photos courtesy of Felicity Norrie.

Answer to Case 766

 Answer to the Parasite Case of the Week 766: Schistosoma haematobium eggs

The following outstanding discussion is written by our guest author, Dr. Azra Hasan.

These are Schistosoma haematobium eggs in a urine sample as many of you correctly identified in the comments. The key giveaway was the prominent “terminal spine”, that helps differentiate S. haematobium from other Schistosoma species. On a closer look we can see that the miracidium (larval stage) fills up the egg. (Be sure to check out case 467 which has incredible videos from Idzi Potters, showing a beautiful motile miracidium!). Note that observing motile miracidia within eggs or in urine serves as a direct indication of an active S. haematobium infection and should be reported.

As noted by Florida Fan, typically, Schistosoma haematobium eggs are found in urine, which is a good way to differentiate them from the similar-appearing, but larger, S. intercalatum, which are found in stool. However, in heavy infections, and especially from residents of endemic areas, one may encounter S. haematobium eggs in stool as well. Rarely, they can also be seen in semen and in biopsy tissues from the bladder, as well as the genitalia and rectum. In endemic regions, nearly 75% women with urinary schistosomiasis have S. haematobium eggs in the genitalia. Female genital schistosomiasis (FGS) is often associated with eggs in the cervix, vagina, and/or vulva, with sandy patch lesions and mucosal bleeding sometimes without hematuria. (2)

Satoshi rightly pointed out the RBCs in the background indicating hematuria - During acute infections, hematuria is an important finding along with history that often includes dysuria and frequent urination. Advanced infections may lead to fibrosis, calcification, obstructive uropathy, polyps, or squamous cell carcinoma of the bladder. Imaging often reveals calcifications described as the "eggshell bladder”.

Praziquantel remains the gold standard drug for treatment, but reinfections are common. Many vaccine candidates show promise and would be the answer in endemic regions. (4)

Here are the primary components of the Schistosoma lifecycle:

• Man is the definitive host who acquires infection by free-swimming cercariae in contaminated freshwater. These penetrate the skin and advance within dermal veins to become the next stage larva. They then move to lungs, systemic circulation, portal circulation, finally developing into adults in the liver. 
• Paired adults male and female worms travel to the vesical and pelvic venous plexus, anchor themselves in the venules surrounding the bladder wall and release eggs.  (Scroll through Case 522 to read the eternal love story of the male and female Schistosoma!) 
• To continue its lifecycle, the eggs penetrate the bladder wall (remember the terminal spine here!) and are excreted in the urine. And while this happens, some eggs get trapped in the bladder tissue. The eggs that are excreted in the urine, hatch into miracidia upon reaching fresh water and seek out their next host – the Bulinus snails.
• Bulinus snails are the intermediate hosts - Miracidia develop asexually into sporocysts which transform into free-swimming cercariae. These are released in fresh water and the cycle continues.

The following are some helpful diagnostic approaches:

• Use of reagent strips to detect hematuria and proteinuria in areas of endemic infection has proven to be an effective screening technique for S. haematobium infections. 
• Eosinophilia has also been used to diagnose infections, 
• S. haematobium eggs are usually detected in the urine. The terminal hematuria portion of the urine specimen may contain numerous eggs trapped in the mucus and pus. Tissue biopsy, vaginal lavage, stool, semen microscopy can be done with clinical suspicion and travel history from endemic regions. (1)
• An antigen-capture ELISA utilizing monoclonal antibodies (MAbs) such as 290-2E6-A and 128C3/3/21 is one of the most promising assays for immunodiagnosis of S. haematobium infections. Antibody detection have not been particularly useful because of cross-reactions with other helminth infections. (5)

Did you know?

• Peak egg excretion occurs between 10am and 2 p.m. Samples collected during this time, or during a 24-h urine collection without preservatives, may be used for examination. It is important to use saline and not water for the urine concentration procedures; this will avoid hatching of the eggs. (Ref: Centre for Disease Control and Prevention (CDC). Schistosomiasis - Diagnostic procedures.)
• The “fetal head” sign is seen in abdominal X rays and is caused by calcium deposits around schistosome eggs in the bladder and uterine walls
• Symptoms are usually not seen for 3 to 6 months or more. This is why S. haematobium infection is listed as a “delayed” cause of hematuria. (3)
• Hematuria is so common that in some areas of endemic infection this phenomenon in boys was considered to be analogous to menarche in girls. 
• S. haematobium infection is endemic in Africa including Caribbean Islands (West Indies), Madagascar, Arabian Peninsula and one limited focus in Maharashtra, India.

Some interesting case reports and reviews:

1. Case Report: A Child with Gross Hematuria and the Importance of Travel History. Shatat IF.  Front Pediatr. 2018 Feb 5; 6:14. doi: 10.3389/fped.2018.00014. PMID: 29459889; PMCID: PMC5807655.
2. Female genital schistosomiasis is a neglected public health problem in Tanzania: Evidence from a scoping review. Mbwanji G, Mazigo HD, Maganga JK, Downs JA. PLoS Negl Trop Dis. 2024 Mar 11;18(3): e0011954. doi: 10.1371/journal.pntd.0011954. PMID: 38466660; PMCID: PMC10927128.
3. Schistosoma haematobium: A Delayed Cause of Hematuria. Tan WP, Hwang T, Park JW, Elterman L.  Urology. 2017 Sep;107: e7-e8. doi: 10.1016/j.urology.2017.06.021. Epub 2017 Jun 23. PMID: 28652164.
4. A comprehensive and critical overview of schistosomiasis vaccine candidates. Al-Naseri A, Al-Absi S, El Ridi R, Mahana N. J Parasit Dis. 2021 Jun;45(2):557-580. doi: 10.1007/s12639-021-01387-w. Epub 2021 Apr 25. PMID: 33935395; PMCID: PMC8068781.
5. Detection of circulating antigens in patients with active Schistosoma haematobium infection. Hassan MM, Medhat A, Makhlouf MM, et al The American journal of tropical medicine and hygiene Am J Trop Med Hyg Am. J. Trop. Med. Hyg. 1998;59(2):295

More information

1. CDC (Centers for Disease Control and Prevention): Schistosomiasis - Parasites (https://www.cdc.gov/parasites/schistosomiasis/)
2. WHO (World Health Organization): Schistosomiasis fact sheet (https://www.who.int/news-room/fact-sheets/detail/schistosomiasis)
3. London School of Hygiene & Tropical Medicine: Schistosomiasis Resources and Research (https://www.lshtm.ac.uk/research/research-action/global-research-portfolio/schistosomiasis)
4. NIH (National Institutes of Health): Schistosomiasis - MedlinePlus (https://medlineplus.gov/schistosomiasis.html)

Parasite Case of the Week 765

This week's case was generously donated by Drs. Cameron Truarn and Damien Bradford from PathWest Laboratory Medicine, and Drs. Huan Zhao and Richard Bradbury from James Cook University, Australia. 

The following objects were noted in a bronchoalveolar lavage from a middle-aged immigrant from Asia, now living in Australia. They measure approximately 1000 micrometers long. What is seen here? Please be as specific as possible.

k

Answer to Case 765

 Answer to the Parasite Case of the Week 765: Strongyloides stercoralis L4 larvae

As noted by Idzi Potters, "The presence of a relatively large genital primordium confirms Strongyloides. The apparently tapered tail (not notched) together with the size of the larva point towards the fourth-stage autoinfective larva (L4)."

For those of you who were thinking these were autoinfective filariform (L3) larvae, you were very close! L4 larvae are the next stage in development after autoinfective L3 larvae and may be potentially detected in human respiratory specimens. Richard Bradbury and his colleagues just published a very interesting article in the Journal of Clinical Microbiology on the presence of L4 S. stercoralis larvae in two separate cases, and we received permission from JCM and the Editor-in-Chief to reproduce some of the images here. 

The major differences between S. stercoralis L3 and L4 larvae are as follows:

• Length: autoinfective L3 are <600 µm and L4 are ~800 µm
• Genital rudiment: small in L3 and elongated in L4 larvae
• Vulva: may be visible in L4 (not L3)
• Tail: L3 is notched whereas L4 is more tapered

Here are some images to illustrate these features; I refer you to the excellent article by Dr. Bradbury and his colleagues for more information, including an image of a L4 larvae/pre-adult female with a vaginal opening. 

Figure legend: Strongyloides stercoralis autoinfective L4 larvae. Abbreviations: An, anus; Bc, buccal cavity; Gr, genital rudiment; Nr, nerve ring; Oes/In, esophageal-intestinal junction.

Thanks again to Drs. Cameron Truarn and Damien Bradford from PathWest Laboratory Medicine, and Drs. Huan Zhao and Richard Bradbury from James Cook University, Australia for donating this interesting case!