  The sporadic accretion following the tidal disruption of a star by a
super-massive black hole (TDE) leads to a bright UV and soft X-ray flare in the
galactic nucleus. The gas and dust surrounding the black hole responses to such
a flare with an echo in emission lines and infrared emission. In this paper, we
report the detection of long fading mid-IR emission lasting up to 14 years
after the flare in four TDE candidates with transient coronal lines using the
WISE public data release. We estimate that the reprocessed mid-IR luminosities
are in the range between $4\times 10^{42}$ and $2\times 10^{43}$ erg~s$^{-1}$
and dust temperature in the range of 570-800K when WISE first detected these
sources three to five years after the flare. Both luminosity and dust
temperature decreases with time. We interpret the mid-IR emission as the
infrared echo of the tidal disruption flare. We estimate the UV luminosity at
the peak flare to be 1 to 30 times $10^{44}$ erg s$^{-1}$ and for warm dust
masses to be in the range of 0.05-1.3 Msun within a few parsecs. Our results
suggest that the mid-infrared echo is a general signature of TDE in the
gas-rich environment.
