Caladrius, according to the Roman mythology, is a snow-white bird that lives in kings' houses. Supposedly, the bird refuses to look at any patient that is not going to make a full recovery. Caladrius existed in the Greek mythology under the name Dhalion.
It is said to also be able to take the sickness into itself and then fly away, dispersing the sickness and healing both itself and the sick person. This is said to be analogous to Jesus Christ, whose crucifixion is said to have drawn out "the sickness" (sin, see Biblical sin-sickness analogy) and, through his "flight" from the grave, saved the sinner.