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Oliver Sacks – Hallucinations

….. the herpes simplex virus, … can attack nerves (including sometimes the olfactory nerves), both impairing and stimulating them. The virus can remain dormant for long periods, sequestered in nerve ganglia, and suddenly re-emerge at intervals of months or years.

One man, a microbiologist, wrote to me:

 "In the summer of 2006,I began to smell things  a faint pervasive odour that I could not identify (my best guess was . . . wet cardboard)."

“Prior to this”, he said “I had a highly sensitive nose, and was able to identify my laboratory cultures by smell alone, or subtle differences in organic solvents, or faint perfumes”

He soon developed a constant hallucination of the smell of rotting fish, which faded only after a year had passed, along with most of his olfactory acuity and the subtlety of most foods.  He wrote:

“Certain odours are completely gone - faeces(!), baking bread, or cookies, roasting turkey, garbage, roses, the fresh soil smell of Streptomyces . . all gone. I miss the smells of Thanksgiving, but not the smell of public toilets”.

The dysosmia and phantosmia were due to a re-emergence of the herpes simplex 2 which he had contracted many years before, and he is intrigued that these are always preceded by hallucinatory smells. He writes,

"I smell the onset of herpes reactivation. A day or two prior to the onset of a neuritis episode, I again have olfactory hallucinations of the last strong smell I noticed. This smell persists during the neuritis and fades as the neuritis fades. . . . The strength of the hallucinations is correlated with the severity of the generalized neuritis".