A phylogeny, or family tree, of coronaviruses, based on
amino acid sequences of an enzyme encoded in their
genome. The virus which causes MERS is labeled in this figure
with HCoV-EMC/2012 for Human Coronavirus (HCoV) and the
case number, and is highlighted in grey. This virus clusters very
tightly with two coronaviruses isolated from bats. Note that the
SARS virus (labeled SARS-CoV) also has a close relationship to
MERS with respect to this sequence being compared.
Source: van Boheemen et al., mBIO, 2013
These results are very preliminary, with a short MERS fragment identified in only a single bat. Specifically, because bats harbor related coronaviruses, some of which are only now being discovered, researchers would like to see more genomic sequence, and isolates from more bats to be sure that virus that causes MERS is indeed harbored by bats. Finally, since bats and humans generally avoid one another, it remains to be seen whether other animals are also part of the infection cycle.
Overall, then, MERS is a deadly infectious disease that can spread from person to person and likely from animal to person. Moreover, mutations in the virus causing MERS could change its infectious properties, and trigger an epidemic of viral pneumonia.
Update: A nice write-up of the detective work involved with these viruses is at Understanding Evolution.