For example, SARS-CoV-2 infection can increase individual vulnerability to PD or parkinsonism, and infections with a relay of microbes (influenza A viruses, SARS-CoV-2, gut microbiota, etc.)and prion-like alpha-synuclein proteins over time can synergize to induce PD or parkinsonism. This evidence concerns the gene SNCA and Parkinson disease.