Answer to Case 502

Answer:Borreliaspp., 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 likelyBorrelia hermsii,one of the tick-borne relapsing feverBorreliaspecies.The other tick-borneBorreliain North America areB. parkeriiandB. turicatae.These species are transmitted through the bite of a soft-bodied tick in the genusOrnithodoros,and are usually associated with exposure to ' rustic ' settings such as cabins and lean-tos.There is a nice article on the geographic distribution ofB. hermsiithat you can readHERE.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. recurrentisinfection has a similar clinical presentation to the tick-borne relapsing fevers, and the spirochetes have an identical appearance on peripheral blood smear.Borreliaspirochetes 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, TreponemaandLeptospiraspp.). O...
Source: Creepy Dreadful Wonderful Parasites - Category: Parasitology Source Type: blogs