The Toluncan ague was a type of influenza.
Every flu season on the USS Voyager, Neelix became convinced that he had Toluncan ague. Rather than arguing with him, The Doctor would simply give him a placebo. In 2376, The Doctor reminded Tom Paris of this when he was planning to leave them for the Qomar homeworld. Paris was already familiar with this fact, having assisted The Doctor for three years. (VOY: "Virtuoso")