There are 3 coronaviruses that cause 13% of colds. Loss of smell is often first symptom in COVID-19 and PD. It has long been a theory that one route to PD is is a viral infection that travels from nose to the deep brain. In the past few days, 6 papers on COVID-19 have cited a 1992 PD paper that shows coronavirus antibodies in brains of PD patients.
ncbi.nlm.nih.gov/pmc/articl...
There is also a theory that PD can start in the gut and get to the brain from there (I don't know that route but they say 1/3 of our neurons are on the gut). Gastrointestinal problems are often the first if not only sign of COVID-19.
Why Is Melatonin Worthy Of Consideration by PwP , Diabetics, People With Covid-19 and Everyone Else ? 
Is there a link between attitudes to covid vaccination and the rejection of conventional medicine in the treatment of PD? 
PD: the gut, covid, etc.
Loss of smell, runny nose, sinusitis connected to PD?
Interventional Influence of the Intestinal Microbiome Through Dietary Intervention and Bowel Cleansing Might Improve Motor Symptoms in PD
