  The dispersive sweep of fast radio bursts (FRBs) has been used to probe the
ionized baryon content of the intergalactic medium, which is assumed to
dominate the total extragalactic dispersion. While the host galaxy
contributions to dispersion measure (DM) appear to be small for most FRBs, in
at least one case there is evidence for an extreme magneto-ionic local
environment and a compact persistent radio source. Here we report the detection
and localization of the repeating FRB 20190520B, which is co-located with a
compact, persistent radio source and associated with a dwarf host galaxy of
high specific star formation rate at a redshift $z=0.241\pm0.001$. The
estimated host galaxy DM $\approx 903^{+72}_{-111}$ pc cm$^{-3}$, nearly an
order of magnitude higher than the average of FRB host galaxies, far exceeds
the DM contribution of the intergalactic medium. Caution is thus warranted in
inferring redshifts for FRBs without accurate host galaxy identifications.
