Scrub typhus — DTM&H MCQ
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Correct answer: A — Doxycycline 100 mg twice daily for 7 days
The correct answer is A, Doxycycline 100 mg twice daily for 7 days. The clinical picture (fever, headache, a painful eschar at the bite site after trekking through scrubland in Southeast Asia) combined with a positive OX-K Weil-Felix reaction is classic for scrub typhus caused by Orientia tsutsugamushi, transmitted by trombiculid mite larvae in scrub vegetation. Doxycycline is the treatment of choice for all rickettsial infections including scrub typhus because it is rapidly bactericidal against obligate intracellular organisms and produces defervescence within 24 to 48 hours; a 7 day course is the standard regimen used in UK and international tropical medicine practice. The eschar and OX-K specificity distinguish this from murine or epidemic typhus (which agglutinate OX-19) and from spotted fever group rickettsioses. Why the other options are wrong: E. Chloramphenicol 500 mg four times daily: an older alternative for rickettsial disease with significant marrow toxicity risk, now reserved for doxycycline-intolerant patients or pregnancy rather than first line use. B. Co-trimoxazole for 14 days: has no reliable activity against Orientia tsutsugamushi and is not a recommended treatment for any rickettsial infection. D. Azithromycin 500 mg daily for 3 days: an evidence based alternative mainly used in pregnant women or young children where tetracyclines are contraindicated, not the first line choice in an otherwise fit adult. C. Ciprofloxacin 500 mg twice daily: fluoroquinolones lack efficacy against rickettsial organisms and have been associated with treatment failure and relapse in scrub typhus. Key point: eschar plus OX-K positive Weil-Felix in a scrub exposed traveller equals scrub typhus, and doxycycline 100 mg twice daily for 7 days is the first line treatment for all rickettsial infections.
Reference: NICE BNF, Doxycycline monograph, indications and dose: rickettsial infection, https://bnf.nice.org.uk/drugs/doxycycline/