Which pathogen is classically associated with post-infectious Guillain-Barré syndrome and what is the mechanism?

• A. Campylobacter jejuni; molecular mimicry leading to autoimmune nerve damage.
• B. Salmonella Typhi; toxin-mediated nerve damage.
• C. Shigella dysenteriae; cross-reactivity causing neuropathy.
• D. ETEC; direct nerve invasion.

Answer: (A)

Post-infectious Guillain-Barré syndrome is an autoimmune attack on the peripheral nerves that is triggered by a prior infection. Campylobacter jejuni is classically associated with this syndrome. The mechanism involves molecular mimicry: certain Campylobacter surface lipooligosaccharides resemble host nerve gangliosides (such as GM1 and GD1a). The antibodies generated against the bacterial components cross-react with these nerve gangliosides, activating complement and damaging the myelin or the axon itself. This immune-mediated injury disrupts nerve conduction and leads to the characteristic ascending weakness of Guillain-Barré syndrome.

Other organisms like Salmonella Typhi, Shigella dysenteriae, or enterotoxigenic E. coli can cause gastroenteritis, but they are not the typical triggers of GBS, and their proposed mechanisms (toxin-mediated damage or direct nerve invasion) do not explain the autoimmune nerve attack seen in this condition.