https://www.ncbi.nlm.nih.gov/pubmed/32014353/

2020 Jan 31. pii: S0248-8663(20)30010-2. doi: 10.1016/j.revmed.2019.12.022. [Epub ahead of print]

Tick-borne relapsing fever : An unrecognized cause of fever in travelers

[Article in French]

Abstract

INTRODUCTION:

Tick-borne relapsing fever is a usual cause of fever in West Africa. Except relapsing febrile episodes, there are no pathognomonic signs and diagnosis is difficult because Borrelia density in patient’s blood is low.

CASE REPORTS:

Tick-borne relapsing fever was revealed by the presence of spirochetes in a blood sample to search malaria in two men, 24 and 31 year-old, returned from Mali.

CONCLUSION:

This diagnosis should be evocated in patients having fever after a trip in infested area, as malaria, both infections can be associated.

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**Comment**

I got news for you.  Borrelia density is low in many patients’ blood.  This is a common problem and one of the reasons why patients continue to test negative.