Harry Kim suffering from Mendakan pox.
Mendakan pox was a disease which was non-fatal and rarely recurred.
Harry Kim suffered from Mendakan pox in 2358. When he was under the influence of a Taresian retrovirus, Kim dreamed about the time of his pox infection and wondered if the disease had recurred in him. The Doctor speculated that his mind sensed his condition and tried to explain it away. He then noted that changes in Kim's blood chemistry were not consistent with a diagnosis of Mendakan pox. (VOY: "Favorite Son")