  We present optical and near-infrared photometry and spectroscopy of the Type
IIn supernova (SN) 2014ab, obtained by the Carnegie Supernova Project II
(CSP-II) and initiated immediately after its optical discovery. We also present
mid-infrared photometry obtained by the Wide-field Infrared Survey Explorer
(WISE) satellite extending from 56 days prior to the optical discovery to over
1600 days. The light curve of SN 2014ab evolves slowly, while the spectra
exhibit strong emission features produced from the interaction between rapidly
expanding ejecta and dense circumstellar matter. The light curve and spectral
properties are very similar to those of SN 2010jl. The estimated mass-loss rate
of the progenitor of SN 2014ab is of the order of 0.1 Msun/yr under the
assumption of spherically symmetric circumstellar matter and steady mass loss.
Although the mid-infrared luminosity increases due to emission from dust, which
is characterized by a blackbody temperature close to the dust evaporation
temperature (~ 2000 K), no clear signatures of in situ dust formation within
the cold dense shell located behind the forward shock are observed in SN 2014ab
in early phases. Mid-infrared emission of SN 2014ab may originate from
pre-existing dust located within dense circumstellar matter that is heated by
the SN shock or shock-driven radiation. Finally, for the benefit of the
community, we also present in an Appendix five near-infrared spectra of SN
2010jl obtained between 450 to 1300 days post discovery.
