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Bitesize evidence: Doxycycline prophylaxis effective for tick-borne relapsing fever

Q Is post-exposure prophylaxis with doxycycline effective at preventing the onset of tick-borne

relapsing fever (TBRF)?


TBRF is an infection caused by spirochetes of the genus Borrelia. Not surprisingly, it is spread by ticks during a blood meal on a host (ie a person). The infection rate is 50 per cent for each tick bite, and the incubation period ranges from two days to 18 days. This study was done in members of the Israeli military training where the disease is endemic.

After the training exercise, any soldier with signs of a tick bite was randomly assigned to receive 200mg doxycycline as an initial dose followed by 100mg daily for four more days or matching placebo.

Participants were monitored closely for symptoms of TBRF and interviewed one week and three weeks after randomisation. Blood samples to test for Borrelia infection were taken 15-21 days after randomisation. Any participants who developed symptoms of TBRF were treated with doxycycline and had blood drawn two weeks after they began.

Of 582 soldiers screened for tick bites, 125 either had a bite or were close contacts of someone who had been bitten and 93 agreed to participate in the study.

Ten cases of TBRF were diagnosed, all in the placebo group and all among patients who actually had evidence of a tick bite. There were no cases of TBRF in the 47 soldiers who received doxycycline prophylaxis.

The Jarisch-Herxheimer reaction did not occur in any patients in the doxycycline prophylaxis group, but occurred in 80 per cent of those treated after the onset of TBRF. Adverse effects of treatment were minor and did not differ from those of placebo.

Level of evidence

1b (see


Hasin T et al. Post-exposure treatment with doxycycline for the prevention of TBRF.

N Engl J Med 2006;355:148-55.

Bottom line

Doxycycline at an initial dose of 200mg followed by four days of 100mg daily effectively prevents tick-borne relapsing fever in patients in a TBRF-endemic area who have evidence of a tick bite.

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