Borrelia recurrentis causes louse-borne relapsing fever. The recurrent febrile episodes are due to which immunological mechanism?

• A Borrelia forms biofilms in blood vessels that periodically shed planktonic organisms during fever spikes
• B Borrelia suppresses B-cell memory formation, causing repeated susceptibility to the same strain
• C Immune complex deposition in renal glomeruli triggers complement activation releasing spirochetes from tissue reservoirs
• D Phase variation: sequential antigenic switching of the variable major protein (VMP) outer membrane proteins through a gene conversion mechanism, allowing new variants to escape antibody-mediated clearance ✓

Explanation

Relapsing fever Borrelia (both B. recurrentis louse-borne and B. hermsii tick-borne) evade host immunity through antigenic variation of their variable major proteins (VMPs — VlsE for B. burgdorferi, VMPs for relapsing fever Borrelia). During each febrile relapse, a new antigenic variant of VMP is expressed through gene conversion (recombination from a large silent vmp gene archive into the expression locus), allowing spirochetes to escape the antibody response generated during the previous episode. This produces the classic recurring fever-clearance-relapse pattern. Each new antigenic variant initiates a new episode until eventually a variant is cleared by cross-reactive immunity or treatment.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.