Case of the Week 461

This week's case was donated by Dr. Peter Gilligan. The patient is a toddler who presented with high fever and tachycardia. The patient had come to the United States from Uganda 16 months prior to presentation and had not traveled outside of the United States since. The following are representative fields from the peripheral blood smear.

Identification?

Answer to Case 461

Answer: Plasmodium vivax infection

This case has several features that are consistent with P. vivax/P. ovale infection; specifically, the size of the infected red blood cells (RBCs) are slightly larger than the neighboring uninfected RBCs, and the timing indicates a relapsed infection which is only seen with these 2 species. We also know that both species are found in Uganda where this patient was from.

Differentiating between P. vivax and P. ovale can then be done by looking at a number of features. The CDC DPDx website has a nice table that compares these features (see the Laboratory Diagnosis panel). In this case, there are some features that are consistent with P. ovale and P. vivax:
1. Some cells have an oval shape suggestive of P. ovale.
2. One field shows an infected cell with a jagged edge suggestive of fimbriations. However, this could just reflect crenations from processing (seen in some of the neighboring RBCs).

3. Many mature schizonts with up to 24 merozoites are seen, consistent with P. vivax. Given this final feature, we make a final identification of P. vivax infection.

In this case, PCR was also positive for P. vivax and did not detect P. ovale, P. falciparum, and P. malariae, thus confirming our morphologic identification.

Case of the Week 460

This week's fun case was donated by Florida Fan. The following motile object was submitted along with an adult Ascaris lumbricoides. Specimen source is stool.

Wet prep:

 Trichrome stain:

Identification?

Answer to Case 460

Answer: Neobalantidium (formerly Balantidium) coli trophozoite

The identification can be made by recognizing the characteristic morphologic features and motility of the N. coli trophozoite. In this case, you can appreciate the circumferential cilia, large size (40 to 200 microns in greatest dimension) and macronucleus (partially seen in this case). The multiple globular structures within the trophozoite likely represent ingested microorganisms and cytoplasmic vacuoles.

The motility of N. coli is commonly described as 'boring', but as Mark Fox mentioned, this term is a bit misleading since there is nothing uninteresting about it! The alternative term, 'rotary', is perhaps a bit more illuminating.

Of note, several readers mentioned that N. coli is associated with pigs and therefore inquired if patient had any pig exposure. Unfortunately we don't have that information in this case. However, this raises the additional point that the patient was also infected with Ascaris and pigs can be also infected with this round worm. Therefore, the case for potential pig exposure is very intriguing!

For those of you that like (or care about) taxonomy, I should mention that Ascaris suum (the species attributed to pigs) is now thought to be the same species as the human parasite, A. lumbricoides. This assertion is based on the numerous morphologic and genetic similarities that have been described between the two (see "Are Ascaris lumbricoides and Ascaris suum a single species?" by Leles et al. HERE). If they are the same species, then the name A. lumbricoides takes precedence since it was described first (1758 vs. 1782). Isn't taxonomy fun?

Case of the Week 459

This week's case is a stool specimen from an elderly man from Kentucky. He reports no travel history outside of the United States. The patient presented with an approximate 50 pound unintentional weight loss over the past several months as well as diarrhea and abdominal cramping.

The following were seen on the stool concentrate (Images courtesy of our Clinical Microbiology Fellow, Dr. Alexandra Bryson):
(10x objective)

(40x objective)

Diagnosis? What forms are seen here?

Answer to Case 459

Answer: Strongyloides stercoralis infection.

Seen here are numerous rhabditiform S. stercoralis larvae, some possible filariform larvae, and embryonated eggs with viable larvae within. This level of infection is consistent with Strongyloides hyperinfection and warrants a rapid call to the clinical team to alert them to the diagnosis.

There were a lot of great comments on this case. Florida Fan, Angelica Maria and Khalid Elfeel nicely discussed the presence of the short buccal cavity and genital primordium - keys feature for differentiating the rhabditiform (L1) larvae of S. stercoralis from the similar-appearing larvae of the hookworm. Shown below is a comparison of the buccal canals of Strongyloides and hookworm rhabditiform larvae (latter courtesy of the CDC DPDx).

Here is an another composite image of the readily-identifiable genital primordium in S. stercoralis rhabditiform larvae (the one in hookworm rhabditiform larvae is inconspicuous).

I should mention that the hookworm larvae come into the differential only when unfixed stool is allowed to sit for more than a day before being examined, thus allowing time for the eggs to mature and hatch. Only unembryonated hookworm eggs are seen in freshly-passed stool, and it takes 1-2 days for the eggs to mature and hatch.

In comparison, seeing S. stercoralis eggs in stool is quite unusual. This is because eggs of S. stercoralis are usually laid in the intestine and quickly hatch to release rhabditiform larvae. Florida Fan, Mark Fox and Sugar Magnolia raised the possibility that the presence of eggs indicates a very high level of infection, which I believe to be correct in this case.

Finally, Anon reminded us that Kentucky is endemic for strongyloidiasis and therefore something that should be considered in patients from this area - especially before starting any immunosuppressive therapy. Along these same lines, you may be interested to see this recent article of hookworm in the American south, published in The American Journal of Tropical Medicine and Hygiene. There is an interesting associated news commentary that you can read HERE. It's so sad to see the poor sanitary and living conditions that are still present in the United States.