Why would Zika virus lead to Guillain–Barré syndrome?
The most curious thing about curiosity is how it makes you think!
Yesterday I wrote “The Other Problem from Zika Virus.” In that article I described how scary Guillain–Barré syndrome (GBS) can be and that it may follow Zika virus infection. Actually, up to two-thirds of the time, GBS starts at the tail end of some infection. Why would that be?
It is not a direct effect of these infections that damages the nerves in GBS. In other words, it does not work like polio. Rather, it is an after-effect of a range of different infections.
About 30% of GBS cases are provoked by Campylobacter jejuni infections which cause diarrhea. A further 10% are attributable to cytomegalovirus(CMV) infections, an entirely different process from Campylobacter. GBS has also been linked, less commonly, to human herpes virus type 6 (HHV-6), Epstein-Barr virus (EBV), varicella zoster virus (VZV), dengue fever, hepatitis E, and now Zika virus. Why would such a diverse group of infections precipitate the same nerve condition as sequela?
The exact cause of GBS is not known. What scientists do know is that the body’s immune system begins to attack the body itself, causing what is known as an autoimmune disease. Usually the cells of the immune system attack only foreign material and invading organisms. In Guillain-Barré syndrome, however, the immune system starts to destroy the myelin sheath that surrounds the axons of many peripheral nerves, or even the axons themselves. (Axons are long, thin extensions of the nerve cells; they carry nerve signals). The myelin sheath surrounding the axon speeds up the transmission of nerve signals and allows the transmission of signals over long distances, so in GBS the longest nerves are affected first.
This may work in several ways. Immune components intended to attack the invading germ may cross react with the myelin sheath. After all, the germs do better in us when they “look” chemically like normal body parts. Alternatively, the infecting virus or bacteria might alter sections of myelin to make them seem foreign to the immune system.
The good news about this murky corner of medical science, is that opportunities to learn more and better prevent or treat GBS are abundant.
Winkler G. Weinberg, MD
I have been an ID physician for over 3 decades. I am the author of No Germs Allowed!. If you liked this article, check out the book on Amazon.