Parkinson’s disease could be triggered by a virus that kills a “good” form of bacteria in the gut. This may lead to a chain reaction of damaged nerves leading from the digestive system up to the brain.

Parkinson’s disease is a progressive disorder of tremors, stiffness and difficulties in moving; it is known to involve the death of nerve cells in the brain, linked with misfolding of a protein found in nerve fibres called synuclein.

Although it has long …