Answer to Case 502

Answer: Borrelia spp., relapsing fever group. Molecular studies are needed to definitively identify the causative agent. However, knowing the exposure history of the patient also helps narrow the differential. In this case, we later found out that the patient is from the northwestern part of North America, and therefore this is most likely Borrelia hermsii, one of the tick-borne relapsing fever Borrelia species. The other tick-borne Borrelia in North America are B. parkerii and B. turicatae. These species are transmitted through the bite of a soft-bodied tick in the genus Ornithodoros, and are usually associated with exposure to 'rustic' settings such as cabins and lean-tos. There is a nice article on the geographic distribution of B. hermsii that you can read HERE.

Borrelia recurrentis, the causative agent of louse-borne relapsing fever, is rarely seen in North America, given that body lice are relatively uncommon and usually associated with overcrowding and social disruption. However, B. recurrentis infection has a similar clinical presentation to the tick-borne relapsing fevers, and the spirochetes have an identical appearance on peripheral blood smear.

Borrelia spirochetes appear as long spiral-shaped bacilli (5-20 microns in length) with relatively regular undulations. As William mentions, there are other spiral-shaped or curved bacteria as well; some are curved or wavy rods (e.g. Vibrio, Campylobacter, Helicobacter), whereas others are true spirochetes (Borrelia, Treponema and Leptospira spp.). Of the true spirochetes, only the relapsing fever Borrelia are regularly seen in blood. Therefore, this thin blood film appearance in conjunction with the clinical history of recurrent (i.e. relapsing) fevers is consistent with tick-borne relapsing fever.

As Blaine and Idzi mention, Borrelia burgdorferi, the primary cause of Lyme disease in North America, does NOT reach sufficient levels in blood to be seen on peripheral blood smear (mean number of spirochetes is 0.1 per mL of blood). Having said that, some mentioned that the newly-described Borrelia mayonii HAS been noted to have high levels of bacteremia in peripheral blood, and therefore could potentially be seen on peripheral blood smear. Good catch! While spirochetes of Borrelia mayonii may be seen on peripheral blood smears, they are in relatively low numbers - ~2 spirochetes per 70 high power fields - so while visible, they would not be in such abundance as seen in this case.

Finally, some of you may be wondering why I've included a bacterial case on this blog devoted to parasites. The reason is that parasitologists can play an important role in identifying other microorganisms when seen on conventional parasitology preparations such as thin blood films. Borrelia spirochetes, Ehrlichia/Anaplasma morulae, and intracellular yeasts (e.g. Histoplasma capsulatum) are the more common non-parasites that can be seen on blood smears, and therefore it's helpful to be familiar with their appearance. We've seen all 3 in just the past year! Here are links to 2 past cases:

Case of the Week 165: Anaplasma phagocytophilum morulae within neutrophils
Case of the Week 492: Histoplasma capsulatum within phagocytic cells

Case of the Week 502

This week's case is of a patient with recurrent fevers. No further history is available, but the following were noted on Giemsa-stained thin blood films:

Identification? What additional test would be helpful for confirming your diagnosis?

Answer to Case 603

Answer to Case of the Week 603: Borrelia sp. spirochetes. The history is most consistent with a relapsing fever Borrelia sp., and subsequent PCR showed this to be Borrelia hermsii. 

As Florida Fan mentioned, this case is a great reminder that when we examine a Giemsa-stained blood film, we may find things other than parasites. In addition to spirochetal bacteria such as in this case, we can find intracellular clusters (morulae) of Anaplasma phagocytophilum and Ehrlichica spp. bacteria, and intracellular years (e.g. Histoplasma capsulatum, Talaromyces marneffei). Leishmania spp. amastigotes can also rarely be seen within phagocytic cells. I've shown Borrelia spirochetes on this blog before (see Case of the Week 502), but never on a thick film, so I thought this would be a nice case to include here.

Note that the spirochetes are uniformly slender with broad undulations. This is different than the microgametes of an exflaggelated Plasmodium sp. microgametocyte which I previously showed on Parasite Case of the Week 595. In that case, I created a composite image of 'squiggly things' seen on a blood smear which may be helpful in identifying and differentiating them:

Some readers asked if the Borrelia species that cause Lyme disease could also be seen on blood film. The answer to this is NO - with one small caveat. The main cause of Lyme in the United States and Canada is Borrelia burgdorferi, whereas in Europe, you can also see B. garinii and B. afzelii. These organisms have extremely low levels of spirochetemia, and therefore spirochetes are NOT seen on peripheral blood films. The only rare exception to this is Borrelia mayonii, an uncommon cause of Lyme disease restricted to the upper Midwestern United States. This organism is actually found in much higher concentrations in the blood, and occasionally a rare spirochete can be seen on peripheral blood smears. We published on this several years ago; you can read the article HERE. (Let me know if you would like a copy).

There were many other good comments posted on this blog case - both in the Comments section and on Twitter - so I would encourage you to read them to learn more about the experiences from our readers.