What percent of hemorrhoids are caused by chronic viral infection of those tissues?

This is actually almost 100% because the condition develops slowly over time, and requires a chronic presence as a smoldering, ongoing, tug-of-war with the immune system attempting to eradicate the presence of invading organisms over a long period of time. As such, hemorrhoids provide a useful diagnostic indicator of this common problem leading to autoimmune disease, and their disappearance a useful confirmation that a thorough body cleanout of harmful viruses has been accomplished through divine healing.