Wednesday, 11 September 2013


I remember last March well. Every morning we turned up at the ID ward at University College Hospital (where the Hospital of Tropical Diseases in London keep their inpatients) to go through the "case of the day". Prof or the specialist registrar would go through the chronological order of the patient's story, and we asked questions in turn (always ask for travel history!), hoping to formulate some plausible and probable diagnoses as we go along. One of the old favourites would be travellers coming back with an eschar*. Again here we saw an old lady with an eschar just on her shoulder - she came in with a fever but otherwise not too unwell.

*a slough or piece of dead tissue that is cast off from the surface of the skin, particularly after a burn injury, but also seen in gangrene, ulcer, fungal infections, necrotizing spider bite wounds, and exposure to cutaneous anthrax

Usually in this case anthrax is not so likely; more often the eschar would have been caused by a tick bite, causing rickettsiosis (and then the disease will be rather confusingly named after the geographical location of where the tick was, see here)

In Asia, however, the rickettsiosis is caused by the intracellular parasite Orientia tsutsugamushi, a Gram-negative α-proteobacterium** of family Rickettsiaceae (so not exactly a rickettsia!). It is named after it was isolated in Japan in 1930 - The disease is thus called scrub typhus, as the mite (similar to tick, but smaller) lives in scrubs.

**Proteobacteria: In this group all are Gram negatives. The group contains many pathogens such as Escherichia, Salmonella, Vibrio and Helicobacter. Because of the great diversity of forms found in this group, the Proteobacteria are named after Proteus, a Greek god of the sea capable of assuming many different shapes

Below is the picture of the tsutsugamushi triangle where scrub typhus is endemic. The rule of thumb is: if you see an eschar on a patient in the triangle, think scrub typhus, give doxycycline for a week (as per most of the eschars). Typhus is a notifiable disease in the UK.

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