To an unworthy Muggle:
The Dark Lord has received your letter, and would have gladly accepted your proposal were it not for your Muggle sensitivities. Upon reading that you had resorted to Muggle remedies to alleviate your suffering, the Dark Lord knew you were not fit for his great cause.
The Dark Lord usually disposes of those who waste his time, but I am certain he had forgotten about you within seconds of setting your letter aflame. However, being his most faithful servant, I have noticed that those who annoy him are often cursed in some way. Since you are a lowly Muggle, I suspect you are now afflicted with a common cold, another silly ailment that Muggles can't cure.
This is your warning to not bother the Dark Lord again; next time he won't be so generous.
Peter Pettigrew, aka Wormtail