Sunday, June 25, 2023

Case of the Week 720

This week's case is generously donated by Dr. Nazia Nagi from Maulana Azad Medical College in New Delhi. The patient is a young, HIV-positive, adult male with diarrhea. The following structures were seen in a wet mount and modified Ziehl-Neelsen stained stool preparations. They measure approximately 35 micrometers long. Identification?

Saturday, June 24, 2023

Answer to Case 720

 Answer to the Parasitology Case of the Week 720: Cystoisospora belli oocysts

These oocysts are easy to differentiate from Cyclospora and Cryptosporidium oocysts based on their large size and ovoid shape. Thanks again to Dr. Nazia Nagi for donating this classic case!

Tuesday, June 20, 2023

Case of the Week 719

This week's case is very timely! The following objects were seen on a modified safranin-stained stool specimen. They measure approximately 8 to 10 micrometers in diameter. Identification?

40x objective:

100x objective:

Monday, June 19, 2023

Answer to Case 719

 Answer to the Parasite of the Week 719: Cyclospora sp. oocysts. 

While Cryptosporidium spp. oocysts have a similar appearance, they are smaller than Cyclospora oocysts, measuring only 4-6 micrometers in diameter. 

Note that Cyclospora oocysts do not stain uniformly with either the modified acid fast or modified safranin methods, although there tends to be fewer unstained oocysts with the latter. The microwave modification of the safranin stain will also improve the staining uniformity (see the CDC procedure HERE).

As Dr. Marc Couturier pointed out on Twitter, there are now three morphologically-identical species of Cyclospora known to cause human infection: C. cayetanensis, C. ashfordi, and C henanensis. Therefore it is best to report this finding out as "Cyclospora species."

Lastly, Idzi discussed in the blog comment sections why this finding is so timely. Every year now in the past decade, the U.S. has seen summer outbreaks of cyclosporiasis linked to imported produce (e.g., cilantro, basil, snap peas, lettuce, raspberries) from Latin America. Infection is transmitted to humans through ingestion of fecally-contaminated food and water. Therefore, infection originates from regions where there is poor sanitation and lack of access to clean water.


Sunday, June 4, 2023

Case of the Week 718

Welcome back to our first case of the month, with a special case from Idzi Potters and the Institute of Tropical Medicine, Antwerp.  The following structures were found in a bronchoalveolar lavage from a middle-aged Belgian patient with asthma who presented with increased shortness of breath. He reports no travel out-of-country and works as an administrator at an insurance company. He recently reported an insect infestation in his home.Video credits are for Monique Vatlet (CHU Ambroise ParĂ©, Mons, Belgium).


Saturday, June 3, 2023

Answer to Case 718

 Answer to the Parasite Case of the Week 718: ciliated epithelial cells; NOT Lophomonas. Many of our readers suspected this case to represent Lophomonas blattarum - a flagellated protozoan parasite of cockroaches - but there is no convincing evidence that Lophomonas is actually a human parasite. Also, there are a number of helpful features that can differentiate ciliated human epithelial cells from L. blattarum:

1. Human ciliate epithelial cells have a well-defined terminal bar with a compact row of short cilia (arrows) rather than the tuft of long flagella possessed by Lophomonas

 This is nicely demonstrated by this additional photograph from the same case:

2. The nucleus is located in a basilar position (rather than apical, as with Lophomonas). 

3. The beating motility of ciliated epithelial cells is very rhythmic and non-direction compared with true Lophomonas.

For those of you who are asking "what about the PCR evidence implicating Lophomonas blattarum as a human pathogen in respiratory samples??" Well, a thorough analysis of the PCR primers conducted by my colleague, Dr. Richard Bradbury revealed these primers to show a lot of cross-reactivity, particularly with the oral trichomonads. Therefore, amplification using this PCR in respiratory specimens would not be conclusively supportive of Lophomonas. Again, though, the difference in motility patterns between ciliated human epithelial cells and Lophomonas are really striking, and allows for definitive differentiation in my mind.