I originally asked this question in r/Herpes and got the suggestion to post it here in r/Virology.

I recently read the article Where Does Herpes Live? that states:

The herpes simplex viruses are latent. After the initial infection, the virus gets into the nerve roots and spreads to the sensory nerve ganglia. The ganglia are the nerve junctions in which nerves from different parts of the body come together. For the genital area, the ganglia are adjacent to the spinal cord in the lower back. For orofacial herpes (cold sores), the ganglia are located behind the cheek bone.

My curiosity is this: How did scientists/doctors/researchers discover where herpes lives? Wouldn't it have been like finding a microscopic needle in a haystack?