The poem moves by association rather than argument, so it helps to read it as a chain of images. It opens with two mouths, a queen's and a horse's, and then asks what will become of "the young disease." Mouths are how things pass between bodies: food, words, kisses, and, as the title suggests, infection. The speaker seems curious more than frightened, treating the question almost like a riddle.
The middle line, "a mouth needs content," plays on the idea that a mouth, like a sling, is useless until something fills it. That could mean food, speech, or a germ. The last lines list evening routines: a husband coming home to his wife, night heading to the coffeehouse, a horse going to a rogue. Each pairing is ordinary, yet each is also a kind of contact, a way things travel from one body or place to another. The mood is dry, quietly playful, and a little uneasy, as if daily life itself were the route the disease takes.