Tuvok had been syphilitic for the last century.
His brain had been boiling in madness making terrible decisions for the last century.
Whic includes loving his wife.
He got syphilis from a man.
He gave syphilis to Janeway,
It was living thinking feeling sentient syphilis and they killed it.
Respecting all life my ass.
It could have been the last of it's kind.
Killing the last representative of a species is genocide.
Someone should have volunteered as a host.
Although if Tuvix had it, then so does Neelix.
Actually looking at the "training" Tuvok had with Kes.
Deeeeeeeeeeeeeeeeeeep sexy Melds to teach her how to control her complete toolbox of abilities.
Tuvok probably gave her Syphilis too, and if left untreated, might explain the unusual behaviors she expressed in her final episode.
So Neelix gave it to kes, or kes gave it to Neelix, if they were playing hide the salami, which some schools of thought argue against.