I just learned from a site about Thoreau that his brother John had died of tuberculosis a couple years before Thoreau lived in the woods. I wonder if by that time he was aware that he had tuberlosis also, and if awareness of his impending early death sought isolation to think.
The site below has a lot of information new to me.
http://www.pbs.org/wnet/ihas/poet/thoreau.html

I long ago wondered why Thoreau never married. At first I thought it was for economic reasons. Then I found his father had a successful business making pencils,which Thoreau took over. And he was a skilled surveyor. So then I wondered if he had a problem with gender. So now it is clear that he must have known he had tuberculosis and a markedly shortened life expectancy. I wonder if he was the source of infection of Emerson, who also died of tuberculosis. In those days so many people thought things like tuberculosis and cancer were punishments for sin, that families concealed them.